Kluane Lake Research Station Bibliography


The Kluane Lake Research Station Bibliography currently contains the following 70 Kluane Red Squirrel Project contributions, which are sorted here by contribution number.


Territory size and ownership in red squirrels : response to removals   /   Price, K.   Broughton, K.   Boutin, S.   Sinclair, A.R.E.
(Canadian journal of zoology, v. 64, no. 5, May 1986, p.1144-1147, ill.)
(Kluane Red Squirrel Project contribution, no. 1)
References.
ASTIS record 19605.
Languages: English
Web: doi:10.1139/z86-172
Libraries: ACU

We monitored size and ownership of red squirrel territories in the southwestern Yukon during the summer following a year of abundant cone crop. Territory boundaries were determined by observing marked individuals. Six individuals and two groups (four individuals per group) were removed to test the hypothesis that the position of territory boundaries are determined by intruder pressure. Removed squirrels were replaced by juveniles or by breeding females which had given up their former territories to their offspring. Replacement occurred within hours of the removal and territory boundaries of the new squirrels were not significantly different from those of the original territory owners. Neighbouring territorial residents did not expand their territories to occupy all or part of the vacated area. The location of territory boundaries were not affected by intruder pressure. (Au)


Manipulation of intruder pressure in red squirrels (Tamiasciurus hudsonicus) : effects on territory size and acquisition   /   Boutin, S.   Schweiger, S.
(Canadian journal of zoology, v. 66, no. 10, Oct. 1988, p.2270-2274, 2 maps)
(Kluane Red Squirrel Project contribution, no. 2)
References.
ASTIS record 58027.
Languages: English
Web: doi:10.1139/z88-337
Libraries: ACU

The effect of intruder pressure on territory size has been investigated in many species of birds but in few species of mammals. We manipulated intruder pressure in an island population (21 adults) of territorial red squirrels (Tamiasciurus hudsonicus) in summer by removing (5) and adding (22) squirrels. When territorial squirrels were removed, neighbouring individuals expanded their territories. Breeding females that did so allowed their young to remain on part of the expanded territory while young from other females settled off the mother's territory. Adding squirrels did not result in a decrease in territory size. Although the introduced squirrels had previously held territories, they did not challenge residents. Instead they behaved as floaters (squirrels without territories); they never called and they occupied areas devoid of territorial squirrels. We conclude that intruder pressure prevents red squirrels from increasing their territory size but increased intruder pressure in the form of floaters or juvenile recruits does not lead to a decrease in territory size. (Au)


Intensity of territorial defense in red squirrels : an experimental test of the asymmetric war of attrition   /   Price, K.   Boutin, S.   Ydenberg, R.
(Behavioral ecology and sociobiology, v. 27, no. 3, Sept. 1990, p. 217-222, ill.)
(Kluane Red Squirrel Project contribution, no. 3)
References.
ASTIS record 60663.
Languages: English
Web: doi:10.1007/BF00180306
Libraries: ACU

Summary: Red squirrels defend exclusive, individual territories year round, 20% to 50% of females do not breed in any given year, and breeding females raise juveniles on their territories. Breeding is asynchronous, and the offspring of early-breeding females are more likely to hold an independently won territory than are late-born offspring. Based on the asymmetric war of attrition, we made the following predictions: (1) squirrels would respond more intensely to the calls of unfamiliar individuals than to the calls of neighbors; (2) breeding females would respond more intensely to unknown calls than would non-breeding females or males; (3) early-breeding females would respond more intensely than would late-breeding females to unknown calls; and (4) all classes of squirrels would respond similarly to the calls of neighbors. Playback experiments supported the predictions. Alternative hypotheses of kin selection, risk of infanticide, and seasonal difference in intruder pressure could not explain the results. (Au)


Territorial bequeathal by red squirrel mothers   /   Price, K.   Boutin, S.
(Behavioral ecology, v. 4, no. 2, Jan. 1993, p. 144-150, ill.)
(Kluane Red Squirrel Project contribution, no. 4)
References.
ASTIS record 60664.
Languages: English
Web: doi:10.1093/beheco/4.2.144
Libraries: ACU

Red squirrels (Tamiasciurus hudsonicus) defend individual, food-based territories year round. These territories are crucial for overwinter survival, yet some female red squirrels in northern populations bequeath their territories to offspring and search for a new one. Bequeathal involves active, strategic dispersal by breeding females. Our study documents this unusual behavior and investigates its correlates in two red squirrel populations in northern Canada. Thirty percent of breeding females dispersed. Bequeathal was related to breeding date, with late-breeding females more often dispersing, but was not related detectably to female condition or territory quality. As an underlying trade-off, early-born juveniles more likely acquired a territory independently, but early-breeding females lost mass and may have increased their risk of territory loss. We suggest that bequeathal has evolved as a consequence of condition dependence in breeding date coupled with limited resources. (Au)


Post-breeding dispersal by female red squirrels (Tamiasciurus hudsonicus) : the effect of local vacancies   /   Boutin, S.   Tooze, Z.   Price, K.
(Behavioral ecology, v. 4, no. 2, Summer 1993, p. 151-155, ill.)
(Kluane Red Squirrel Project contribution, no. 5)
References.
ASTIS record 58025.
Languages: English
Web: doi:10.1093/beheco/4.2.151
Libraries: ACU

Red squirrels (Tamiasciurus hudsonicus) defend food-based territories year round, and juveniles must acquire a territory before winter to survive. We experimentally removed territory owners during the time that juveniles were becoming independent to examine the effect of local vacancies on dispersal patterns. Juveniles attempted to take over removal territories most frequently. However, females with offspring still on the natal territory actually took over twice as many territories as juveniles. These females did not appear to move because of low reproductive potential or to increase territory quality. Instead, moving to a removal territory allowed more of their offspring to remain on the natal territory, which appeared to increase juvenile survival. (Au)


Does food availability affect growth and survival of males and females differently in a promiscuous small mammal, Tamiasciurus hudsonicus?   /   Boutin, S.   Larsen, K.W.
(Journal of animal ecology, v. 62, no. 2, Apr. 1993, p. 364-370, ill.)
(Kluane Red Squirrel Project contribution, no. 6)
References.
ASTIS record 53350.
Languages: English
Web: doi:10.2307/5367
Libraries: ACU

Summary: 1. In dimorphic mammals, males grow faster than females, but often suffer higher mortality during periods of resource shortage. 2. We compared growth and survival of males and females in a promiscuous small mammal with a relatively small degree of dimorphism (male/female body mass ratios ranged from 1.05 to 1.11). 3. We compared two geographically distinct populations over 4 years during which natural food levels varied considerably. We also experimentally supplemented and reduced food levels. 4. Birth weights and preweaning growth rates did not differ between sexes, but growth rates differed between years. 5. Survival to weaning was lower in males than in females in one year and one population only. This followed a winter of complete failure of the cone crop, the primary food source. 6. Post-weaning growth rates of males and females differed in some years but regardless of the degree of difference, post-weaning survival rates of the two sexes were equal. 7. Experimental addition and reduction of food did not affect growth or survival of the two sexes differently. 8. We conclude that changing resource levels do not affect growth and survival of male and female red squirrels differently. (Au)


Costs of escalated territorial defence in red squirrels   /   Stuart-Smith, A.K.   Boutin, S.
(Canadian journal of zoology, v. 72, no. 6, June 1994, p.1162-1167, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 53)
(Kluane Red Squirrel Project contribution, no. 7)
References.
ASTIS record 53718.
Languages: English
Web: doi:10.1139/z94-156
Libraries: ACU

The costs of escalated territorial defence have not been well-documented, although in theoretical studies they are often assumed to be high. We manipulated territorial defence in red squirrels (Tamiasciurus hudsonicus) to assess the costs of territorial disputes in terms of energy, reproductive status, and predation. Feeders containing sunflower seeds were used to manipulate foraging behaviour and induce territorial disputes. Experimental squirrels displayed dramatically higher rates of territorial behaviours in response to feeders, and while there was no difference in survival between experimental and control squirrels, in 4 of the 17 disputes territory owners lost their territories. All 3 females that did so suffered reproductive costs. Territorial disputes were won by the heavier squirrels in all 12 cases where contestants were of different masses, but where the contestants were of similar masses (4 of 5 cases), territory owners were more likely to win. (Au)


Predation on red squirrels during a snowshoe hare decline   /   Stuart-Smith, A.K.   Boutin, S.
(Canadian journal of zoology, v. 73, no. 4, Apr. 1995, p. 713-722, ill., maps)
(Kluane Boreal Forest Ecosystem Project contribution, no. 48)
(Kluane Red Squirrel Project contribution, no. 8)
References.
ASTIS record 53727.
Languages: English
Web: doi:10.1139/z95-083
Libraries: ACU

We examined the extent and impact of predation on red squirrels (Tamiasciurus hudsonicus) during a cyclic decline of snowshoe hares in the southwestern Yukon, Canada. We monitored survival of squirrels on three control grids and a predator exclosure from March 1991 through August 1993. On controls, adult survival during the breeding season decreased from 1991, when snowshoe hare populations were high, to 1992, when hare populations declined rapidly. Survival increased slightly in 1993, when hare and predator populations were very low. Similarly, adult survival during winter was lower in 1992-1993 than in 1991-1992. Adult survival on the exclosure remained similar in each breeding season but declined during winter 1992-1993. Adult survival was similar on the controls and the exclosure in each year except during winter 1991-1992 and the 1992 breeding season, when it was lower on the controls. There was no difference in juvenile survival between the controls and the exclosure. Despite the decrease in adult survival due to predation, there was no population decline on any of the control grids. We conclude that predation did not have a measurable impact on red squirrel densities at Kluane and that it is unlikely red squirrels show 10-year population cycles in conjunction with snowshoe hares. (Au)


Behavioural differences between surviving and depredated juvenile red squirrels   /   Stuart-Smith, A.K.   Boutin, S.
(Écoscience, v. 2, no 1, 1995, p. 34-40, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 54 [79])
(Kluane Red Squirrel Project contribution, no. 9)
References.
ASTIS record 33416.
Languages: English
Web: doi:10.1080/11956860.1995.11682266
Libraries: ACU

Individuals killed by predation often are considered to be in poorer physical condition than those not killed, but little work has been done on behavioural differences between the two. We monitored the behaviour, movements and survival of 15 juvenile red squirrels (Tamiasciurus hudsonicus) from the first day of their emergence through late summer to determine behavioural characteristics associated with predation. Individuals which spent relatively less time vigilant, less time resting, and more time in exposed locations were more likely to be depredated. The distance moved by an individual during observation periods was not related to its survival, but individuals that spent relatively more time off their natal territory were more likely to be depredated. Adult red squirrels spent significantly less time in exposed places than juveniles, which may relate to the lower depradation rates experienced by adults. (Au)


DHEA effects on brain and behavior : insights from comparative studies of aggression   /   Soma, K.K.   Rendon, N.M.   Boonstra, R.   Albers, H.E.   Demas, G.E.
(Essential role of DHEA (dehydroepiandrosterone) and sex steroid formation (intracrinology)
/ Edited by F. Labrie. The Journal of steroid biochemistry and molecular biology, v.145, Jan. 2015, p. 261-272, ill.)
(Kluane Red Squirrel Project contribution, no. ?)
Indexed a PDF file from the Web.
References.
ASTIS record 80546.
Languages: English
Web: doi:10.1016/j.jsbmb.2014.05.011

Historically, research on the neuroendocrinology of aggression has been dominated by the paradigm that the brain receives sex steroid hormones, such as testosterone (T), from the gonads, and then these gonadal hormones modulate behaviorally relevant neural circuits. While this paradigm has been extremely useful for advancing the field, recent studies reveal important alternatives. For example, most vertebrate species are seasonal breeders, and many species show aggression outside of the breeding season, when the gonads are regressed and circulating levels of gonadal steroids are relatively low. Studies in diverse avian and mammalian species suggest that adrenal dehydroepiandrosterone (DHEA), an androgen precursor and prohormone, is important for the expression of aggression when gonadal T synthesis is low. Circulating DHEA can be converted into active sex steroids within the brain. In addition, the brain can synthesize sex steroids de novo from cholesterol, thereby uncoupling brain steroid levels from circulating steroid levels. These alternative mechanisms to provide sex steroids to specific neural circuits may have evolved to avoid the costs of high circulating T levels during the non-breeding season. Physiological indicators of season (e.g., melatonin) may allow animals to switch from one neuroendocrine mechanism to another across the year. DHEA and neurosteroids are likely to be important for the control of multiple behaviors in many species, including humans. These studies yield fundamental insights into the regulation of DHEA secretion, the mechanisms by which DHEA affects behavior, and the brain regions and neural processes that are modulated by DHEA. It is clear that the brain is an important site of DHEA synthesis and action. (Au)


Does reproductive synchrony affect juvenile survival rates of northern mammals?   /   O'Donoghue, M.   Boutin, S.
(Oikos, v. 74, no. 1, Oct. 1995, p. 115-121, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 67)
(Kluane Red Squirrel Project contribution, no. 10)
References.
ASTIS record 53770.
Languages: English
Web: doi:10.2307/3545680
Libraries: ACU

Predator swamping is often cited as an adaptive function of reproductive synchrony. We measured juvenile survival rates of two boreal mammals, snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus), and evaluated the effect of timing of birth relative to the population mean on subsequent survival. Reproduction of hares was highly synchronous. Juvenile hares were born in three distinct litter groups per summer, and they suffered high early mortality due to predation. Juveniles born closest to the population mean had higher survival than those born later for two of the three litter groups. The timing of red squirrel litters was more variable, and squirrels only had one litter per summer. The juvenile survival rates of squirrels were high relative to those of hares. Degree of synchrony had no effect on survival rates of juvenile squirrels to emergence or from emergence to weaning. We suggest that predation selects for tighter reproductive synchrony of snowshoe hares, at least while they are at peak densities, but that it has little effect on the timing of red squirrel reproduction. (Au)


Population changes of the vertebrate community during a snowshoe hare cycle in Canada's boreal forest   /   Boutin, S.   Krebs, C.J.   Boonstra, R.   Dale, M.R.T.   Hannon, S.J.   Martin, K.   Sinclair, A.R.E.   Smith, J.N.M.   Turkington, R.   Blower, M.   Byrom, A.   Doyle, F.I.   Doyle, C.   Hik, D.   Hofer, L.   Hubbs, A.   Karels, T.   Murray, D.L.   Nams, V.   O'Donoghue, M.   Rohner, C.   Schweiger, S.
(Oikos, v. 74, no. 1, Oct. 1995, p. 69-80, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 68)
(Kluane Red Squirrel Project contribution, no. 11)
References.
ASTIS record 39829.
Languages: English
Web: doi:10.2307/3545676
Libraries: ACU

We measured the density changes of 22 species of vertebrates during a snowshoe hare cycle in northern Canada. Hares were the dominant herbivore in the system and changes in their numbers were correlated with changes in numbers of arctic ground squirrel, spruce grouse, ptarmigan, lynx, coyote, great horned owl, goshawk, raven and hawk owl. Hare numbers were not correlated with numbers of red-backed vole which showed peaks during the low, increase, and early decline phases of the hare cycle. Hawk owls were the only predator whose numbers correlated with changes in red-backed voles while boreal owls and weasels were correlated with densities of Microtus. Red squirrel, American kestrel, red-tailed hawk, northern harrier, wolverine, magpie and gray jay showed no correlation with hare or vole numbers. We conclude that species in the boreal forest of Canada do not exhibit the strong synchrony found between voles and other members of the verterbrate community in northern Fennoscandia. We discuss some of the possible reasons for these differences. (Au)


Reproductive demands and mass gains : a paradox in female red squirrels (Tamiasciurus hudsonicus)   /   Humphries, M.M.   Boutin, S.
(Journal of animal ecology, v. 65, no. 3, May 1996, p. 332-338)
(Kluane Red Squirrel Project contribution, no. 12)
References.
ASTIS record 43154.
Languages: English
Web: doi:10.2307/5879
Libraries: ACU

Summary: 1. We studied the response of lactating red squirrels to reproductive demands that were experimentally increased by litter-size manipulations. 2. Females with experimentally increased reproductive demands ('augment' females) gained significantly more body mass during the first half of lactation than did unmanipulated ('control') females. However, augment females lost more mass following the mid-point of lactation than control females, so that the net mass difference between early lactation and late summer was negligible for both treatments. 3. Measurements of total body water at the mid-point of lactation confirmed that mass gains during early lactation reflected changes in body fat levels, indicating that females adjusted their energy stores according to their reproductive demands. 4. We also analysed the relationship between early lactation mass gain and natural litter size among a larger group of control females, studied at the same site between 1990 and 1994. There was a significant, positive relationship between natural litter size and female mass gain. Furthermore, females characterized by the largest gains in body mass had the highest levels of juvenile survival to emergence, indicating that early lactation mass gain is an important component of parental investment. 5. These responses suggest that (i) energy storage during early lactation is used to reduce daily energy requirements during late lactation; (ii) breeders use demands during early lactation to 'forecast' requirements during late lactation; and (iii) that despite the elevated energetic demands of lactation, individuals can quickly adjust their energy budgets from slightly positive to highly positive levels. (Au)


Mass-dependent reproduction or reproduction-dependent mass? A comment on body mass and first-time reproduction in female sciurids   /   Humphries, M.M.   Boutin, S.
(Canadian journal of zoology, v. 77, no. 1, Jan. 1999, p. 171-173)
(Kluane Red Squirrel Project contribution, no. 13)
References.
ASTIS record 47417.
Languages: English
Web: doi:10.1139/cjz-77-1-171
Libraries: ACU

We question the validity of Svendsen and White's conclusion that body mass affects the timing of primiparity in eastern chipmunks (Tamias striatus) (G.E. Svendsen and M.M. White. Can. J. Zool. 75: 1891-1895, 1997 ). Because the masses of reproductive and non-reproductive females were measured during the postpartum period only, the differences reported by Svendsen and White may be due to reproductive females gaining more mass than non-reproductive females between the premating and postpartum periods. We evaluated the plausibility of this alternative explanation by comparing the body mass of reproductive and non-reproductive female red squirrels (Tamiasciurus hudsonicus). Like Svendsen and White, we found that postpartum reproductive females were significantly heavier than non-reproductive females, but contrary to their interpretation, these differences did not exist during the premating period. We conclude that primiparity in female sciurids may not be mass-dependent, but rather that postpartum mass differences may occur because reproductive females augment their energy reserves to help sustain reproductive demands during late lactation. (Au)


The determinants of optimal litter size in free-ranging red squirrels   /   Humphries, M.M.   Boutin, S.
(Ecology, v. 81, no. 10, Oct. 2000, p.2867-2877, ill.)
(Kluane Red Squirrel Project contribution, no. 14)
References.
ASTIS record 60665.
Languages: English
Web: doi:10.2307/177347
Libraries: ACU

Food availability, energetic ceilings, and life-history trade-offs have been proposed as potential determinants of offspring number in many animals. We investigated the role of these factors in determining litter size in a free-ranging population of red squirrels (Tamiasciurus hudsonicus). Long-term observational data were used to assess the influence of food availability, while experimental manipulations of litter size permitted evaluation of the importance of energetic ceilings and life-history trade-offs. Among unmanipulated litters, juvenile growth rate and survival, but not litter size, were significantly related to annual food supply. Experimental increases in offspring number were successfully sustained in a high- and a low-food year, but in both years increases in litter sizes were associated with pronounced declines in juvenile growth rates. However, the reduced size of offspring in augmented litters did not fully compensate for the increase in offspring number, so that the total litter mass supported by augmented females was much higher than that of control females. During late lactation, augmented females were characterized by increased daily energy expenditure, but not by significant changes in time budgets, relative to control females. Increases in litter size did not appear to reduce maternal survival, but were associated with declines in offspring survival. Together, these results indicate that food availability and energetic ceilings do not limit litter size in red squirrels directly, but that tradeoffs between offspring number and offspring survival may eliminate any advantage of weaning larger-than-normal litters. (Au)


Breeding dispersal in female North American red squirrels   /   Berteaux, D.   Boutin, S.
(Ecology, v. 81, no. 5, May 2000, p.1311-1326, ill.)
(Kluane Red Squirrel Project contribution, no. 15)
References.
ASTIS record 53334.
Languages: English
Web: doi:10.2307/177210
Libraries: ACU

Although natal dispersal has received considerable attention from animal ecologists, the causes and consequences of breeding dispersal have remained largely unexplored. We used telemetry, direct observation, and long-term mark-recapture (9 yr) to study breeding dispersal in the North American red squirrel (Tamiasciurus hudsonicus) at Kluane, Yukon, Canada. We recorded the postbreeding behavior (keep the territory, share it with juveniles, or bequeath it to juveniles) of mothers from 485 litters, and monitored the fates of eight cohorts of weaned juveniles (680 individuals). The proportion of mothers that bequeathed their territory to one of their offspring was roughly one-third of that keeping or sharing it. Breeding dispersal was a recurrent phenomenon that characterized a fraction of the population of reproductive females every year. Dispersing females did not improve the quality of their breeding environment. In contrast, by leaving their territory, mothers allowed some offspring to stay on the natal site, which increased juvenile survival. Breeding dispersal by female red squirrels was thus a form of parental investment. Dispersing females were older than others, had higher numbers of juveniles at weaning, and moved their breeding sites more frequently after reproducing when food availability was high. These patterns are consistent with the major predictions of parental investment theories. We detected no difference in survivorship or future reproduction between dispersing and resident mothers. Juvenile males dispersed more often than females, but not farther. The sex of offspring did not influence whether mothers dispersed or not. Although we showed that breeding dispersal can have major impacts on the dynamics of squirrel populations, the relative implications of natal and breeding dispersal for the genetic structure and demography of populations and the social evolution of species remain unknown. (Au)


The role of red squirrels and arctic ground squirrels   /   Boonstra, R.   Boutin, S.   Byrom, A.   Karels, T.   Hubbs, A.   Stuart-Smith, K.   Blower, M.   Antpoehler, S.
In: Ecosystem dynamics of the boreal forest : the Kluane project / Edited by C.J. Krebs, S. Boutin and R. Boonstra. - New York : Oxford Press, 2001, ch. 9, p. 180-214, ill., map
(Kluane Red Squirrel Project contribution, no. 16)
References.
ASTIS record 60666.
Languages: English
Libraries: ACU

A consistent feature throughout the boreal forest of North America is the rattle call of the red squirrel, Tamiasciurus hudsonicus, as it advertises its whereabouts to con-specifics. Like the snowshoe hare, the red squirrel's distribution encompasses the entire boreal forest (see figure 2.7). The "keek keek" call of a second squirrel species, the arctic ground squirrel (Spermophilus parry ii, the siksik of the Inuit), is also heard in the boreal forests of northwestern North America (Banfield 1974). In terms of biomass of herbivores in these forests, these two squirrels are the second and third most important, respectively, after snowshoe hares (see figure 1.2). Both squirrel species could serve as alternate food sources for the many predators who eat primarily snowshoe hares. However, before our study, no one had investigated experimentally the possible linkages between populations of these squirrels and the snowshoe hare population cycle. The conventional wisdom is that any link would be a secondary one, as predators switch from hares to squirrels during the hare decline. Though both squirrels are active during the summer and thus potentially available to predators, only red squirrels remain active during the long boreal winter and are one of the few alternate prey available to hare predators. (Au)


Maternal effects and the potential for evolution in a natural population of animals   /   McAdam, A.G.   Boutin, S.   Réale, D.   Berteaux, D.
(Evolution, v. 56, no. 4, Apr. 2002, p. 846-851, ill.)
(Kluane Red Squirrel Project contribution, no. 17)
References.
ASTIS record 53362.
Languages: English
Web: doi:10.1554/0014-3820(2002)056[0846:MEATPF]2.0.CO;2
Libraries: ACU

Maternal effects are widespread and can have dramatic influences on evolutionary dynamics, but their genetic basis has been measured rarely in natural populations. We used cross-fostering techniques and a long-term study of a natural population of red squirrels, Tamiasciurus hudsonicus, to estimate both direct (heritability) and indirect (maternal) influences on the potential for evolution. Juvenile growth in both body mass and size had significant amounts of genetic variation (mass h² = 0.10; size h² = 0.33), but experienced large, heritable maternal effects. Growth in body mass also had a large positive covariance between direct and maternal genetic effects. The consideration of these indirect genetic effects revealed a greater than three-fold increase in the potential for evolution of growth in body mass (h²t = 0.36) relative to that predicted by heritability alone. Simple heritabilities, therefore, may severely underestimate or overestimate the potential for evolution in natural populations of animals. (Au)


Edge effects on survival and behaviour of juvenile red squirrels (Tamiasciurus hudsonicus)   /   Anderson, E.M.   Boutin, S.
(Canadian journal of zoology, v. 80, no. 6, June 2002, p.1038-1046, ill.)
(Kluane Red Squirrel Project contribution, no. 18)
References.
ASTIS record 51841.
Languages: English
Web: doi:10.1139/z02-087
Libraries: ACU

Much research has examined parasitism and predation rates on avian nests within the context of edge effects. Few studies, however, have considered the influence that behavioural compensation for high predation risk may have on subsequent survival rates and edge effects. We attempted to determine whether juvenile red squirrels (Tamiasciurus hudsonicus) experience edge effects by comparing the survival and behaviour of individuals born along a forest edge with those of individuals born in the forest interior. A combination of telemetry, direct observation, and livetrapping was used to determine the fate of juveniles born during the summers of 1987 through 1998 and the behaviour of juveniles born during the summers of 1997 and 1998 in Kluane, Yukon. There were no differences in survival between edge and interior juveniles from birth to emergence but there was a trend towards higher survival rates for edge juveniles from emergence to weaning. Behavioural differences between edge and interior juveniles were consistent with these survival differences: edge juveniles spent less time travelling and foraging and more time resting near the time of weaning than did interior juveniles. Edge and interior mothers differed little behaviourally during the early emergence period. The significant differences in juvenile behaviour which we found suggest that behaviour may indeed moderate differences in predation risk between edge and interior habitats and thus should be considered in other studies that examine the influence of edges on survival or nest predation. (Au)


Genetic and plastic responses of a northern mammal to climate change   /   Réale, D.   McAdam, A.G.   Boutin, S.   Berteaux, D.
(Proceedings of the Royal Society of London. Series B. Biological sciences, v.270, no.1515, 22 Mar. 2003, p. 591-596, ill.)
(Kluane Red Squirrel Project contribution, no. 19)
References.
ASTIS record 43079.
Languages: English
Web: doi:10.1098/rspb.2002.2224

Climate change is predicted to be most severe in northern regions and there has been much interest in to what extent organisms can cope with these changes through phenotypic plasticity or microevolutionary processes. A red squirrel population in the southwest Yukon, Canada, faced with increasing spring temperatures and food supply has advanced the timing of breeding by 18 days over the last 10 years (6 days per generation). Longitudinal analysis of females breeding in multiple years suggests that much of this change in parturition date can be explained by a plastic response to increased food abundance (3.7 days per generation). Significant changes in breeding values (0.8 days per generation), were in concordance with predictions from the breeder's equation (0.6 days per generation), and indicated that an evolutionary response to strong selection favouring earlier breeders also contributed to the observed advancement of this heritable trait. The timing of breeding in this population of squirrels, therefore, has advanced as a result of both phenotypic changes within generations, and genetic changes among generations in response to a rapidly changing environment. (Au)


Lifetime selection on heritable life-history traits in a natural population of red squirrels   /   Réale, D.   Berteaux, D.   McAdam, A.G.   Boutin, S.
(Evolution, v. 57, no. 10, 2003, p.2416-2423, ill.)
(Kluane Red Squirrel Project contribution, no. 20)
References.
ASTIS record 57200.
Languages: English
Web: doi:10.1554/02-346
Libraries: ACU

Despite their importance in evolutionary biology, heritability and the strength of natural selection have rarely been estimated in wild populations of iteroparous species or have usually been limited to one particular event during an organism's lifetime. Using an animal-model restricted maximum likelihood and phenotypic selection models, we estimated quantitative genetic parameters and the strength of lifetime selection on parturition date and litter size at birth in a natural population of North American red squirrels, Tamiasciurus hudsonicus. Litter size at birth and parturition date had low heritabilities (h² = 0.15 and 0.16, respectively). We considered potential effects of the environmental covariances between phenotypes and fitness and of spatial environmental heterogeneity in estimates of selection. Selection favored early breeders and females that produced litter sizes close to the population average. Stabilizing selection on litter size at birth may occur because of a trade-off between number of offspring produced per litter and offspring survival or a trade-off between a female's fecundity and her future reproductive success and survival. (Au)


Variation in viability selection among cohorts of juvenile red squirrels (Tamiasciurus hudsonicus)   /   McAdam, A.G.   Boutin, S.
(Evolution, v. 57, no. 7, July 2003, p.1689-1697, ill.)
(Kluane Red Squirrel Project contribution, no. 21)
References.
ASTIS record 60667.
Languages: English
Web: doi:10.1554/02-393
Libraries: ACU

Selection will result in observable changes in traits only if it acts consistently in space and time, but few estimates of selection in natural populations have been temporally replicated. Here we estimate viability selection on nestling growth rates for 13 cohorts (1989-2001) of red squirrels (Tamiasciurus hudsonicus) from a natural population located in southwestern Yukon, Canada. Directional selection on nestling growth rates varied in magnitude and direction from one cohort to the next. The magnitude of directional selection was relatively weak in most years (median ß' = 0.24), but there were episodes of very strong viability selection (ß' > 0.5) in some cohorts. We found no evidence of significant stabilizing or disruptive selection on this trait. Examination of viability selection episodes over shorter time periods suggested that the strength of selection on juveniles in this population was positively related to the time scale over which selection was measured. Viability selection from birth to emergence from the natal nest (50 days of age) and from emergence to successful recruitment (100 days of age) were positively correlated, but were both independent of selection on nestling growth rates from recruitment to potential breeding age (one year). The strength of directional selection on growth rates prior to recruitment was negatively correlated with spring temperature whereas selection from recruitment to breeding was positively correlated with the abundance of spruce cones produced in the previous fall. Episodes of strong directional selection from birth to breeding age appear to be due to potentially rare combinations of environmental conditions. As a result, predicting the occurrence of very strong episodes of selection will be extremely difficult, but predicting the microevolutionary responses to observed selection on individual cohorts remains feasible. (Au)


Effects of food abundance on genetic and maternal variation in the growth rate of juvenile red squirrels   /   McAdam, A.G.   Boutin, S.
(Journal of evolutionary biology, v. 16, no. 6, Nov. 2003, p. 1249-1256, ill.)
(Kluane Red Squirrel Project contribution, no. 22)
References.
ASTIS record 60668.
Languages: English
Web: doi:10.1046/j.1420-9101.2003.00630.x
Libraries: ACU

Sources of variation in growth in body mass were assessed in natural and experimental conditions of high and low food abundance using reciprocal cross-fostering techniques and long-term data (1987-2002) for a population of North American red squirrels (Tamiasciurus hudsonicus). Growth rates were significantly higher in naturally good and food supplemented conditions, than in poor conditions. Mother-offspring resemblance was higher in poor conditions as a result of large increases in both the direct genetic variance and direct-maternal genetic covariance and a smaller increase in the coefficient of maternal variation. Furthermore, the genetic correlation across environments was significantly less than one indicating that sources of heritable variation differed between the two environments. These results are consistent with the hypothesis that selection has eroded heritable variation for growth more in good conditions and indicate the potential for independent adaptation of growth rates in good and poor conditions. (Au)


Maternal effects and the response to selection in red squirrels   /   McAdam, A.G.   Boutin, S.
(Proceedings of the Royal Society of London. Series B. Biological sciences, v.271, no.1534, 7 Jan. 2004, p. 75-79, ill.)
(Kluane Red Squirrel Project contribution, no. 23)
References.
ASTIS record 60669.
Languages: English
Web: doi:10.1098/rspb.2003.2572
Libraries: ACU

Mothers often provide much of the early environment for their offspring. These maternal effects are predicted to result in unusual evolutionary dynamics in offspring traits if they are themselves heritable, but these important predictions have not previously, to our knowledge, been tested in the wild. Here, we quantified the responses of red squirrels (Tamiasciurus hudsonicus) to documented episodes of natural selection and found support for both of the fundamental predictions of models that describe maternal effect evolution. First, changes in juvenile growth rates across one generation of selection were five times greater than predicted by heritability (h2) alone, but were consistent with the additional contribution of maternal genetic effects. Second, responses to selection were influenced not only by the strength of selection in the current generation, but also by selection in the previous generation, indicating the presence of evolutionary momentum. These results were in agreement with predictions of a simple model including litter size as the only maternal effect, and provide, to our knowledge, the first empirical evidence for the importance of maternal effects to evolutionary dynamics in a natural population. (Au)


Keeping pace with fast climate change : can Arctic life count on evolution?   /   Berteaux, D.   Réale, D.   McAdam, A.G.   Boutin, S.
(Biology of the Canadian Arctic : a crucible for change in the 21st century. Integrative and comparative biology, v. 44, no. 2, Apr. 2004, p. 140-151, ill.)
(Kluane Red Squirrel Project contribution, no. 24)
References.
Papers from the Symposium "Biology of the Canadian Arctic: a crucible for change in the 21st century" presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 4-8 January 2003 in Toronto.
ASTIS record 57199.
Languages: English
Web: doi:10.1093/icb/44.2.140
Libraries: ACU

Adaptations to the cold and to short growing seasons characterize arctic life, but climate in the Arctic is warming at an unprecedented rate. Will plant and animal populations of the Arctic be able to cope with these drastic changes in environmental conditions? Here we explore the potential contribution of evolution by natural selection to the current response of populations to climate change. We focus on the spring phenology of populations because it is highly responsive to climate change and easy to document across a wide range of species. We show that evolution can be fast and can occur at the time scale of a few decades. We present an example of reproductive phenological change associated with climate change (North American red squirrels in the Yukon), where a detailed analysis of quantitative genetic parameters demonstrates contemporary evolution. We answer a series of frequently asked questions that should help biologists less familiar with evolutionary theory and quantitative genetic methods to think about the role of evolution in current responses of ecological systems to climate change. Our conclusion is that evolution by natural selection is a pertinent force to consider even at the time scale of contemporary climate changes. However, all species may not be equal in their capacity to benefit from contemporary evolution. (Au)


Isolation of 18 polymorphic microsatellite loci from the North American red squirrel, Tamiasciurus hudsonicus (Sciuridae, Rodentia), and their cross-utility in other species [primer note]   /   Gunn, M.R.   Dawson, D.A.   Leviston, A.   Hartnup, K.   Davis, C.S.   Srobeck, C.   Slate, J.   Coltman, D.W.
(Molecular ecology notes, v. 5, no. 3, Sept. 2005, p. 650-653)
(Kluane Red Squirrel Project contribution, no. 25)
References.
ASTIS record 60670.
Languages: English
Web: doi:10.1111/j.1471-8286.2005.01022.x
Libraries: ACU

We isolated 18 polymorphic microsatellite loci to be used for pedigree analysis in a wild population of North American red squirrels, Tamiasciurus hudsonicus. Allelic diversity and observed heterozygosity ranged from six to 13 and 0.39 to 0.89, respectively, in a sample of 93 individuals. Up to 13 sets of primers also amplify in other rodent species. (Au)


A visual index for estimating cone production for individual white spruce trees   /   LaMontagne, J.M.   Peters, S.   Boutin, S.
(Canadian journal of forest research, v. 35, no. 12, Dec. 2005, p.3020-3026, ill.)
(Kluane Red Squirrel Project contribution, no. 26)
References.
ASTIS record 60676.
Languages: English
Web: doi:10.1139/X05-210
Libraries: ACU

The number of cones produced by coniferous trees is commonly estimated by visual counts from the ground of a portion of the tree multiplied by a simple conversion factor. Linear conversion factors have been used to estimate total cone production by white spruce (Picea glauca (Moench) Voss). However, these conversion factors originate from other coniferous species and were often based on assumptions of cone visibility within the crown and not on empirical data. We propose a simple method for estimating the total number of cones produced by individual white spruce. We counted visible cones (an index of cone production, or cone index) on a total of 60 trees located in Alberta and Yukon, Canada, that were then felled and all cones were counted. We found that log(actual total cones) = 0.073 + 1.189 × log(cone index) is more accurate for estimating total cone numbers for white spruce than are other conversion factors (ranging from total cones = 1.5 × cone index to total cones = 3.35 × cone index), as determined using Akaike's information criterion with small sample bias adjustment and a validation data set. The relationship between the index of cone production and actual total cones produced is nonlinear, which is contrary to that proposed for various Pinus species. (Au)


Expenditure freeze : the metabolic response of small mammals to cold environments   /   Humphries, M.M.   Boutin, S.   Thomas, D.W.   Ryan, J.D.   Selman, C.   McAdam, A.G.   Berteaux, D.   Speakman, J.R.
(Ecology letters, v. 8, no. 12, Dec. 2005, p.1326-1333, ill.)
(Kluane Red Squirrel Project contribution, no. 27)
References.
ASTIS record 60677.
Languages: English
Web: doi:10.1111/j.1461-0248.2005.00839.x
Libraries: ACU

There is renewed focus on the ecological determinants of animal metabolism and recent comparative analyses support the physiological expectation that the field metabolic rate (FMR) of homeotherms should increase with declining ambient temperature. However, sustained elevation of FMR during prolonged, seasonal cold could be prevented by intrinsic limits constraining FMR to some multiple of basal metabolic rate (BMR) or extrinsic limits on resource abundance. We analysed previous measures of mammalian FMR and BMR to establish the effect of ambient temperature on both traits and found no support for intrinsic limitation. We also measured the FMR of a northern population of red squirrels (Tamiasciurus hudsonicus) exposed to ambient temperatures much colder than all but one previous study of mammal FMR. These measurements revealed levels of energy expenditure that are, unexpectedly, among the lowest ever recorded in homeotherms and that actually decrease as it gets colder. Collectively, these results suggest the metabolic niche space of cold climate endotherms may be much larger than previously recognized. (Au)


Best squirrels trade a long life for an early reproduction   /   Descamps, S.   Boutin, S.   Berteaux, D.   Gaillard, J.-M.
(Proceedings of the Royal Society of London. Series B. Biological sciences, v.273, no.1599, 22 Sept. 2006, p.2369-2374, ill.)
(Kluane Red Squirrel Project contribution, no. 28)
References.
ASTIS record 60678.
Languages: English
Web: doi:10.1098/rspb.2006.3588
Libraries: ACU

Age at primiparity plays a crucial role in population dynamics and life-history evolution. Long-term data on female North American red squirrels were analysed to study the fitness consequences of delaying first reproduction. Early breeders were born earlier, had a higher breeding success and achieved a higher lifetime reproductive success than females who delayed their first reproduction, which suggests a higher quality of early breeders. However, early breeders had similar mass when tagged, and similar number of food caches available at one year of age as late breeders. Nevertheless, we found evidence of survival costs of early primiparity. Early breeders had a lower survival between one and two years of age than late breeders and a lower lifespan. Our study points out that two reproductive tactics co-occurred in this population: a tactic based on early maturity at the cost of a lower survival versus a tactic based on delayed maturity and long lifespan. High quality individuals express the most profitable tactic by breeding early whereas low quality individuals do the best of a bad job by delaying their first reproduction. (Au)


Red squirrels (Tamiasciurus hudsonicus) feeding on spruce bark beetles (Dendroctonus rufipennis) : energetic and ecological implications   /   Pretzlaw, T.   Trudeau, C.   Humphries, M.M.   LaMontagne, J.M.   Boutin, S.
(Journal of mammalogy, v. 87, no. 5, Oct. 2006, p. 909-914, ill.)
(Kluane Red Squirrel Project contribution, no. 29)
References.
ASTIS record 60679.
Languages: English
Web: doi:10.1644/05-MAMM-A-310R1.1
Libraries: ACU

We report the novel occurrence of North American red squirrels (Tamiasciurus hudsonicus) feeding on spruce bark beetle (Dendroctonus rufipennis) larvae, and consider the energetic and ecological implications. Although a bark beetle outbreak was 1st noted at our study site in 1994, significant feeding on them by red squirrels was not observed until 2002, after which there was significant increase in the prevalence of autumn beetle foraging by squirrels into 2003. This increase corresponded with a decrease in spruce seed availability, the squirrels' preferred food source. Spruce bark beetles currently represent an important food source, with 73% of monitored squirrels engaged in beetle feeding in autumn 2003, providing 20% of daily energy requirements. In autumn 2002 and 2003, the density of beetle-infested trees on a squirrel's territory was a significant predictor of whether it fed on beetle larvae but not the proportion of its foraging bouts involving bark beetles. Feeding on larval spruce bark beetles by red squirrels represents a short-term solution to a climate-mediated beetle outbreak that will ultimately reduce local spruce seed production and habitat suitability for red squirrels. (Au)


Anticipatory reproduction and population growth in seed predators   /   Boutin, S.   Wauters, L.A.   McAdam, A.G.   Humphries, M.M.   Tosi, G.   Dhondt, A.A.
(Science, v.314, no.5807, 22 Dec. 2006, p.1928-1930, ill.)
(Kluane Red Squirrel Project contribution, no. 30)
References.
ASTIS record 60680.
Languages: English
Web: doi:10.1126/science.1135520
Libraries: ACU

Mast seeding, the intermittent, synchronous production of large seed crops by a population of plants, is a well-known example of resource pulses that create lagged responses in successive trophic levels of ecological communities. These lags arise because seed predators are thought capable of increasing reproduction and population size only after the resource pulse is available for consumption. The resulting satiation of predators is a widely cited explanation for the evolution of masting. Our study shows that both American and Eurasian tree squirrels anticipate resource pulses and increase reproductive output before a masting event, thereby increasing population size in synchrony with the resource pulse and eliminating the population lag thought to be universal in resource pulse systems. (Au)


A test of the efficacy of whole-genome amplification on DNA obtained from low-yield samples   /   Gunn, M.R.   Hartnup, K.   Boutin, S.   Slate, J.   Coltman, D.W.
(Molecular ecology notes, v. 7, no. 3, May 2007, p. 393-399, ill.)
(Kluane Red Squirrel Project contribution, no. 31)
References.
ASTIS record 61275.
Languages: English
Web: doi:10.1111/j.1471-8286.2007.01696.x
Libraries: ACU

Conservation and population genetic studies are sometimes hampered by insufficient quantities of high quality DNA. One potential way to overcome this problem is through the use of whole genome amplification (WGA) kits. We performed rolling circle WGA on DNA obtained from matched hair and tissue samples of North American red squirrels (Tamiasciurus hudsonicus). Following polymerase chain reaction (PCR) at four microsatellite loci, we compared genotyping success for DNA from different source tissues, both pre- and post-WGA. Genotypes obtained with tissue were robust, whether or not DNA had been subjected to WGA. DNA extracted from hair produced results that were largely concordant with matched tissue samples, although amplification success was reduced and some allelic dropout was observed. WGA of hair samples resulted in a low genotyping success rate and an unacceptably high rate of allelic dropout and genotyping error. The problem was not rectified by conducting PCR of WGA hair samples in triplicate. Therefore, we conclude that WGA is only an effective method of enhancing template DNA quantity when the initial sample is from high-yield material. (Au)


Genetic relatedness of mates does not predict patterns of parentage in North American red squirrels   /   Lane, J.E.   Boutin, S.   Gunn, M.R.   Slate, J.   Coltman, D.W.
(Animal behaviour, v. 74, no. 3, Sept. 2007, p. 611-619, ill.)
(Kluane Red Squirrel Project contribution, no. 32)
Appendix.
References.
ASTIS record 63287.
Languages: English
Web: doi:10.1016/j.anbehav.2006.12.017
Libraries: ACU

Previously limited to laboratory studies, the deleterious effects of inbreeding are now being revealed in a number of wild systems. Female North American red squirrels, Tamiasciurus hudsonicus, show high levels of multimale mating and little to no overt precopulatory mate selection. We hypothesized that the negative repercussions of inbreeding should select for a female's ability to select sperm from more distantly related males. Consequently, successful sires should be less genetically related to the female than are unsuccessful males. We tested this hypothesis using both an analysis of absolute success among all copulating males and also relative success of sires within multiply sired litters. Pairwise genetic relatedness and paternity were determined through molecular analysis of tissue samples collected from reproductive females, copulating males and resultant offspring. In contrast to other systems, we found no evidence that the genetic similarity of mates predicts patterns of parentage in red squirrels. Genetic relatedness did not predict whether a copulating male would sire any offspring, and relative success of sires within multiply sired litters was unrelated to their relatedness to the dam of the litter. Furthermore, selection for inbreeding avoidance mechanisms may be minimal, as there were no observable negative fitness repercussions to inbreeding. We detected no relationship between the genetic relatedness of an offspring's parents and its neonatal mass, growth rate or survival to reproductive age. In red squirrels, we found no evidence of parentage patterns based on genetic similarity of mates, and this phenomenon may be less universal than previously thought. (Au)


Life histories of female red squirrels and their contributions to population growth and lifetime fitness   /   McAdam, A.G.   Boutin, S.   Sykes, A.K.   Humphries, M.M.
(Écoscience, v. 14, no 3, Sept. 2007, p. 362-369, ill.)
(Kluane Red Squirrel Project contribution, no. 33)
References.
ASTIS record 63289.
Languages: English
Web: doi:10.2980/1195-6860(2007)14[362:LHOFRS]2.0.CO;2
Libraries: ACU

The potential importance of life history traits to population growth rates has been well explored theoretically but has rarely been documented in wild mammals. In this study we used 18 consecutive years of data from a population of North American red squirrels (Tamiasciurus hudsonicus) in the southwest Yukon, Canada, to examine variation in female life history traits and their consequences for population growth rate. Red squirrels in this population experienced severe juvenile mortality, but survivorship beyond age 2 followed a Type I relationship where the annual survival probability decreased with age. Maximum lifespan was 8 y. Some females initiated breeding as yearlings, but most delayed first breeding until 2 y of age or in some cases even later. Annual reproduction generally involved the production of a single litter averaging 3.1 offspring (range: 1 to 7); however, some females attempted a second litter within a single breeding season, either following reproductive failure or, in rare circumstances, after a successful first breeding attempt. Life table characteristics for the 11 cohorts born between 1987 and 1997 indicated a population growth rate close to zero (r = 0.009). Elasticity analysis as well as individual population projection matrices and lifetime reproductive success data indicated that early survival and not age at first reproduction was most strongly associated with a female's contribution to population growth. Lifespan accounted for 83.9% of the variation in population growth rate and was positively correlated with age at first reproduction, such that females who bred as yearlings suffered decreased longevity. Collectively, these results emphasize the importance of female survival and not reproductive output to population growth and lifetime fitness in this system. (Au)


Persistent maternal effects on juvenile survival in North American red squirrels   /   Kerr, T.D.   Boutin, S.   LaMontagne, J.M.   McAdam, A.G.   Humphries, M.M.
(Biology letters, v. 3, no. 3, June 22, 2007, p. 289-291, ill.)
(Kluane Red Squirrel Project contribution, no. 34)
References.
ASTIS record 61773.
Languages: English
Web: doi:10.1098/rsbl.2006.0615
Libraries: ACU

Maternal effects can have lasting fitness consequences for offspring, but these effects are often difficult to disentangle from associated responses in offspring traits. We studied persistent maternal effects on offspring survival in North American red squirrels (Tamiasciurus hudsonicus) by manipulating maternal nutrition without altering the post-emergent nutritional environment experienced by offspring. This was accomplished by providing supplemental food to reproductive females over winter and during reproduction, but removing the supplemental food from the system prior to juvenile emergence. We then monitored juvenile dispersal, settlement and survival from birth to 1 year of age. Juveniles from supplemented mothers experienced persistent and magnifying survival advantages over juveniles from control mothers long after supplemental food was removed. These maternal effects on survival persisted, despite no observable effect on traits normally associated with high offspring quality, such as body size, dispersal distance or territory quality. However, supplemented mothers did provide their juveniles an early start by breeding an average of 18 days earlier than control mothers, which may explain the persistent survival advantages their juveniles experienced. (Au)


Local-scale synchrony and variability in mast seed production patterns of Picea glauca   /   Lamontagne, J.M.   Boutin, S.
(Journal of ecology, v. 95, no. 5, Sept. 2007, p. 991-1000, ill.)
(Kluane Red Squirrel Project contribution, no. 35)
References.
ASTIS record 63290.
Languages: English
Web: doi:10.1111/j.1365-2745.2007.01266.x
Libraries: ACU

Summary: 1. Mast seeding is the synchronous and highly variable production of seed by a population of plants. Mast seeding results from the behaviour of individuals; however, little is known about the synchrony of individuals at local scales. 2. We address two primary questions at a within-population (17-36 ha study plots) and individual level: (i) How variable is seed production between and within years? (ii) How synchronized is seed production between individuals? 3. We monitored annual cone production of 356 Picea glauca (white spruce) from 1990 to 2005 within four plots spanning a total distance of 5.3 km in the Yukon Territory, Canada. 4. Spearman correlations (rs) were conducted to test for synchrony. Overall, the trees were moderately synchronous (mean rs (± SE) of 0.52 ± 0.14), and synchrony was statistically detectable (rs > 0) over all distances. Individuals < 75 m apart were highly synchronous (0.64 ± 0.18), and correlations dropped to 0.33 ± 0.07 for trees > 3 km apart. There was considerable variation in cone production patterns among pairs of individuals. 5. The number of mast years per plot varied from one to three. During a mast year, many individuals within plots produced large cone crops, with more variability between individuals in low mean cone years. Individual trees had dominant endogenous cycles varying from none to 1-5 years. Forty-four percent of trees had no significant lag, 23% a negative 1-year lag, and 20% a positive 3-year lag. Basal area did not influence lags, but trees with higher mean cone production throughout the study were more likely to have a 3-year lag compared with no lag. 6. The scale of highest synchrony coincided with the scale at which the dominant seed predator in the area, the territorial red squirrel (Tamiasciurus hudsonicus), operates. This may be the scale at which selection for synchrony occurs. 7. Based on high synchrony locally, high synchrony within a mast year, and multiple lags in cone production by individuals, both available resources and strong weather cues appear to play roles in the observed patterns. (Au)


Female red squirrels fit Williams' hypothesis of increasing reproductive effort with increasing age   /   Descamps, S.   Boutin, S.   Bertreaux, D.   Gaillard, J.-M.
(Journal of animal ecology, v. 76, no. 6, Nov. 2007, p.1192-1201, ill.)
(Kluane Red Squirrel Project contribution, no. 36)
References.
ASTIS record 63295.
Languages: English
Web: doi:10.1111/j.1365-2656.2007.01301.x
Libraries: ACU

Summary: 1. Williams predicted that reproductive effort should increase as individuals age and their reproductive value declines. This simple prediction has proven difficult to test because conventional measures of energy expenditure on reproduction may not be a true reflection of reproductive effort. 2. We investigated age-specific variation in female reproductive effort in a stable population of North American red squirrels where energy expenditure on reproduction is likely to reflect actual reproductive effort. We used seven measures of reproductive effort spanning conception to offspring weaning. 3. We found that females completed growth by age 3 and that reproductive value decreased after this age likely because of reproductive and survival senescence. We therefore, predicted that reproductive effort would increase from age 3 onwards. 4. The probability of breeding, litter mass at weaning, and likelihood of territory bequeathal were all lower for 1- and 2-year-old females than for females older than 3 years, the age at which growth is completed. That growing females are faced with additional energetic requirements might account for their lower allocation to reproduction as compared with older females. 5. The probability of attempting a second reproduction within the same breeding season and the propensity to bequeath the territory to juveniles increased from 3 years of age onwards, indicating an increase in reproductive effort with age. We think this increase in reproductive effort is an adaptive response of females to declining reproductive values when ageing, thereby supporting Williams' prediction. (Au)


The interaction between personality, offspring fitness and food abundance in North American red squirrels   /   Boon, A.K.   Réale, D.   Boutin, S.
(Ecology letters, v. 10, no. 11, Nov. 2007, p.1094-1104, ill.)
(Kluane Red Squirrel Project contribution, no. 37)
References.
ASTIS record 63296.
Languages: English
Web: doi:10.1111/j.1461-0248.2007.01106.x
Libraries: ACU

Animal personality is now frequently reported in wild and captive populations. It has been shown to be moderately heritable and to have potentially important fitness consequences. Variation in personality within a population may be maintained by balancing selection if different values of personality traits are favoured under different conditions. We measured personality in 98 female North American red squirrels (Tamiasciurus hudsonicus Erxleben), and examined whether its variation could be maintained by changing selection pressures acting via reproductive traits and yearly variation in food abundance. There was no effect of personality on parturition date or litter size, but a female's activity was correlated to the growth rate of her offspring in the nest, and her aggressiveness was correlated to their survival in the nest and overwinter. The magnitude and direction of the effects changed among life history stages and years, possibly in association with food supply in some cases, and may indicate a role for balancing selection in the maintenance of personality. (Au)


Cohort effects in red squirrels : the influence of density, food abundance and temperature on future survival and reproductive success   /   Descamps, S.   Boutin, S.   Berteaux, D.   McAdam, A.G.   Gaillard, J.-M.
(Journal of animal ecology, v. 77, no. 2, Mar. 2008, p. 305-314, ill.)
(Kluane Red Squirrel Project contribution, no. 38)
References.
ASTIS record 63427.
Languages: English
Web: doi:10.1111/j.1365-2656.2007.01340.x
Libraries: ACU

1. Environmental conditions experienced early in life may have long-lasting effects on individual performance, thereby creating 'silver-spoon effects'. 2. We used 15 years of data from a North American red squirrel (Tamiasciurus hudsonicus Erxleben) population to investigate influences of food availability, density and spring temperature experienced early in life on reproduction and survival of female squirrels during adulthood. 3. We found that spring temperature and food availability did not affect female survival after 1 year of age, whereas higher squirrel densities led to lower survival, thereby affecting longevity and lifetime fitness. 4. In addition, both food availability experienced between birth and weaning, and spring temperature in the year of birth, had long-lasting positive effects on female reproductive success. These results emphasize the critical effect environmental conditions during the early life stages can have on the lifetime performance of small mammals. 5. These long-term effects of early food and temperature were apparent only once we controlled for conditions experienced during adulthood. This suggests that silver-spoon effects can be masked when conditions experienced early in life are correlated to some environmental conditions experienced later in life. 6. The general importance of silver-spoon effects for adult demographic performance might therefore be underestimated, and taking adult environment into account appears to be necessary when studying long-term cohort effects. (Au)


Female multiple mating and paternity in free-ranging North American red squirrels   /   Lane, J.E.   Boutin, S.   Gunn, M.R.   Slate, J.   Coltman, D.W.
(Animal behaviour, v. 75, no. 6, June 2008, p.1927-1937, ill.)
(Kluane Red Squirrel Project contribution, no. 39)
References.
ASTIS record 65144.
Languages: English
Web: doi:10.1016/j.anbehav.2007.10.038
Libraries: ACU

Multimale mating (MMM) is common in female mammals, but our understanding of its evolutionary significance in this taxon lags behind that in others (e.g. invertebrates and birds). To date, the majority of research on mammalian MMM has been conducted under laboratory conditions, and the extent to which these findings have relevance for natural populations is little known. We quantified MMM in a free-ranging population of North American red squirrels, Tamiasciurus hudsonicus, and investigated its hypothesized influences and consequences. We observed 85 mating chases, representing 62 individual females, over three mating seasons and calculated standardized indexes of MMM and number of copulations. Extrinsic elements of mating chases (i.e. an index of the number of attending males and date) explained variation in MMM, while traits of the females (age and pre-oestrous body mass) did not correlate with MMM. Hypotheses of cryptic direct benefit (fertility assurance and infanticide avoidance) were not supported because MMM did not influence pregnancy rate, litter size or nest fate. There was also no correlation between MMM and offspring quality, multiple paternity or litter allelic diversity, and therefore, no support for hypotheses of genetic benefit. In addition to not accruing observable benefits to MMM, females did not incur a detectable cost, thus rendering MMM selectively neutral. Rather, in line with traditional explanations, female mating behaviour in red squirrels appears to be a passive response to selection on multifemale mating in males. (Au)


Age-specific variation in survival, reproductive success and offspring quality in red squirrels : evidence of senescence   /   Descamps, S.   Boutin, S.   Berteaux, D.   Gaillard, J.-M.
(Oikos, v.117, no. 9, Sept. 2008, p.1406-1416, ill.)
(Kluane Red Squirrel Project contribution, no. 40)
Supplementary material (available online as Appendix 016545 at <www.oikos.ekol.lu.se/appendix>) Appendix 1 and 2.
References.
ASTIS record 65145.
Languages: English
Web: doi:10.1111/j.0030-1299.2008.16545.x
Libraries: ACU

Individual performance is expected to decrease with age because of senescence. We analyzed long-term data collected on a North American red squirrel population to assess the influence of age on body mass, survival and reproductive performance, and to study the effects of sex and of environmental conditions during early life on senescence patterns. Mass of males and females did not decrease at the end of life, possibly because body mass mostly reflects overall size in income breeders such as red squirrels. On the other hand, we found evidence of senescence in survival of both sexes and, to a lesser extent, in female reproductive traits. When compared to females, males had both higher survival and delayed decrease in survival, suggesting a weaker senescence in males. The offspring survival from weaning to one year of age also decreased with increasing mother age. This suggests that older females produce juveniles of lower quality, providing evidence of an intergenerational effect of mother's age on juveniles' fitness. Finally, our results indicate that variations in food conditions during early life influenced the reproductive tactics of females in the first years of their life, but not senescence patterns. (Au)


Plasma DHEA levels in wild, territorial red squirrels : seasonal variation and effect of ACTH   /   Boonstra, R.   Lane, J.E.   Boutin, S.   Bradley, A.   Desantis, L.   Newman, A.E.M.   Soma, K.K.
(General and comparative endocrinology, v.158, no. 1, Aug. 2008, p. 61-67, ill.)
(Kluane Red Squirrel Project contribution, no. 41)
References.
ASTIS record 65149.
Languages: English
Web: doi:10.1016/j.ygcen.2008.05.004
Libraries: ACU

In many species, territorial behavior is limited to the breeding season and is tightly coupled to circulating gonadal steroid levels. In contrast, both male and female red squirrels (Tamiasciurus hudsonicus) are highly aggressive in both the breeding and non-breeding seasons in defense of food stores on their individual territories throughout the boreal and northern forests of North America. Dehydroepiandrosterone (DHEA), an androgen precursor, is secreted from the adrenal cortex in some mammals, and DHEA has been linked to aggression in non-breeding songbirds. Here, we examined plasma DHEA levels in a natural population of red squirrels in the Yukon, Canada. Plasma DHEA levels in both males and females reached high concentrations (up to 16.952 ng/ml in males and 14.602 ng/ml in females), markedly exceeding plasma DHEA concentrations in laboratory rats and mice and similar to plasma DHEA concentrations in some primates. Circulating DHEA levels showed both seasonal and yearly variation. Seasonal variation in male plasma DHEA levels was negatively correlated with testes mass. Yearly variation in male DHEA levels was positively correlated with population density. In both males and females, circulating DHEA rapidly increased after ACTH treatment, implying an adrenal origin. This is the first examination of plasma DHEA concentrations in a wild rodent and the first field experiment on the regulation of plasma DHEA in any wild mammal. These data lay the foundation for future studies on the role of DHEA in non-breeding territoriality in this species and other mammals. (Au)


Maternal effects on evolutionary dynamics in wild small mammals   /   McAdam, A.G.
In: Maternal effects in mammals / Edited by D. Maestripieri and J.M. Mateo. - Chicago : University of Chicago Press, 2009, ch. 4, p. 64-82, ill.
(Kluane Red Squirrel Project contribution, no. 42)
References.
ASTIS record 77735.
Languages: English
Libraries: ACU

... In wild mammals, maternal effects can play an important role in both adaptation to variable environmental conditions and evolutionary dynamics. Most empirical studies of maternal effects in mammals, however, have focused on environmental maternal effects on offspring traits and their fitness consequences. In contrast, the paucity of empirical studies of genetic maternal effects on evolutionary dynamics in the wild represents a potentially large gap in our understanding of the evolutionary process in wild mammals. In this chapater, I focus on genetic rather than environmental maternal effects, presenting an overview of their potential importance to evolutionary dynamics. I then review some of my work on a natural population of North American red squirrels (Tamiasciurus hudsonicus) in which we have quantified all of the necessary parameters for testing predictions of models of maternal-effect evolution in the wild. Finally, I discuss some of the implications of genetic maternal effects and maternal-effect evolution for internally driven population cycles in small mammals (sensu Chitty 1967). (Au)


Personality, habitat use, and their consequences for survival in North American red squirrels, Tamiasciurus hudsonicus   /   Boon, A.K.   Réale, D.   Boutin, S.
(Oikos, v.117, no. 9, Sept. 2008, p.1321-1328, ill.)
(Kluane Red Squirrel Project contribution, no. 43)
References.
ASTIS record 65148.
Languages: English
Web: doi:10.1111/j.0030-1299.2008.16567.x
Libraries: ACU

Personality affects many aspects of an individual's behaviour, life history and fitness, and has been shown to be moderately heritable in wild populations. Correlations between personality and risk-taking that lead to life history tradeoffs could act to maintain variation in personality within a population, but this has not yet been tested. In this study, we used females from a marked population of North American red squirrels in Kluane, Yukon, to determine whether personality predicts risk-taking in the wild, and whether these risk-taking behaviours result in life history tradeoffs. We measured personality in open field and mirror image stimulation tests and extracted two traits, activity and aggressiveness, using principal component analysis and mixed model techniques. Using trapping records for individuals from February to September 2005, we obtained three measures of risk-taking: the number of trapping events, the number of different trapping locations, and the maximum distance between the home territory and a trapping event. We used GLMs to determine whether the activity and aggressiveness of individuals are related to these risk-taking behaviours, and found that active squirrels were trapped significantly more frequently and at a greater number of locations. There was also a significant interaction between activity and aggressiveness to affect the maximum capture distance. To determine if there are fitness tradeoffs associated with these risk-taking behaviours, we examined female bequeathal behaviour and survival. Bequeathing a territory increases offspring probability of overwinter survival, and we found that an increasing number of trapping locations was associated with an increasing tendency to bequeath. Active females were less likely to survive until the following spring. Risk-taking is therefore predicted by personality in this population, and they affect both survival and territorial bequeathal. These fitness tradeoffs may therefore lead to the maintenance of variation in personality. (Au)


Sexually selected behaviour : red squirrel males search for reproductive success   /   Lane, J.E.   Boutin, S.   Gunn, M.R.   Coltman, D.W.
(Journal of animal ecology, v. 78, no. 2, Mar. 2009, p. 296-304, ill.)
(Kluane Red Squirrel Project contribution, no. 44)
References.
ASTIS record 68269.
Languages: English
Web: doi:10.1111/j.1365-2656.2008.01502.x
Libraries: ACU

Summary: 1. Differential male reproductive success is commonplace in mammals and frequently attributed to variation in morphological traits that provide individuals with a competitive advantage in female defence mating systems. Other mammalian mating systems, however, have received comparatively little attention and correlates of male reproductive success in them are less well understood. 2. We studied a free-ranging population of North American red squirrels (Tamiasciurus hudsonicus Erxleben) exhibiting year-round individual territoriality. Males must temporarily vacate their territories to locate spatially dispersed receptive females, thereby setting the stage for a scramble competition mating system. 3. We predicted that both male annual mating success (measured as the number of females copulated with) and annual reproductive success (measured as the number of offspring sired) would be positively correlated with both search ability (measured as the number of oestrous females located over the mating season) and effort (measured as mating season home range size), generating directional sexual selection on these two metrics. 4. Mating season home ranges of males showed, on average, an almost 10-fold increase relative to those measured during the nonmating season, while those of females showed a more moderate twofold increase and both annual mating and reproductive success of males was positively correlated with search ability and search effort. 5. The spatial dispersion of females, resulting from the strict territorial social structure of red squirrels, gave rise to a predicted scramble competition mating system. Furthermore, the strength of sexual selection on behavioural traits in this mating system equalled previous estimates for morphological traits in female defence mating systems. (Au)


Survival costs of reproduction vary with age in North American red squirrels   /   Descamps, S.   Boutin, S.   McAdam, A.G.   Berteaux, D.   Gaillard, J.-M.
(Proceedings of the Royal Society of London. Series B. Biological sciences, v.276, no.1659, 22 Mar. 2009, p. 119-1135, ill.)
(Kluane Red Squirrel Project contribution, no. 45)
Appendices: electronic supplementary material is available at http://dx.doi.org/10.1098/rspb.2008.1401 or via http://journals.royalsociety.org.
References.
ASTIS record 70706.
Languages: English
Web: doi:10.1098/rspb.2008.1401
Libraries: ACU

The costs of reproduction are expected to be higher under unfavourable conditions, so that breeding in years of low food supply should have important costs. In addition, the costs of reproduction may be contingent on the age of individuals, and young growing and old senescent individuals should suffer higher costs than the prime-age ones. We tested these predictions by investigating the costs of reproduction as a function of food availability and age in female North American red squirrels using the long-term data on survival and reproduction. We found that the costs of reproduction were independent of food supply, and we did not detect any trade-off between the current and future reproduction. We also did not detect any survival cost of reproduction for the prime-age females, but found evidence for survival costs in yearlings and old (6 years or above) females with successfully breeding individuals having a lower chance of survival compared with unsuccessful or non-breeding ones. These results supported our prediction that the costs of reproduction depended on the age of female red squirrels and were higher in young growing and old senescent individuals. Our study also indicated that, in contrast to large herbivores, heterogeneity in individual quality and viability selection in red squirrels do not affect the study of trade-offs and of the age variation in life-history traits. (Au)


Lactating red squirrels experiencing high heat load occupy less insulated nests   /   Guillemette, C.U.   Fletcher, Q.E.   Boutin, S.   Hodges, R.M.   McAdam, A.G.   Humphries, M.M.
(Biology letters, v. 5, no. 2, Apr. 23, 2009, p. 166-168, ill.)
(Kluane Red Squirrel Project contribution, no. 46)
References.
ASTIS record 70708.
Languages: English
Web: doi:10.1098/rsbl.2008.0592
Libraries: ACU

The heat dissipation limit hypothesis suggests that the capacity for lactating mammals to transfer energy to their offspring through milk may be constrained by limits on heat dissipation, particularly in species that raise offspring in well-insulated nests. We tested a prediction of this hypothesis by evaluating whether lactating free-ranging red squirrels (Tamiasciurus hudsonicus) occupy less insulated nests when experiencing conditions that increase heat load. In support of the hypothesis, when climate normal ambient temperatures were warm, squirrels supporting large litter masses of furred offspring occupied nests of lower insulative value. These results support the heat dissipation limit hypothesis and suggest that free-ranging mammals may select nests based on their insulative value, not only to reduce heat loss in cold conditions but also to dissipate heat during periods of heat stress. (Au)


Why do North American red squirrel, Tamiasciurus hudsonicus, mothers relocate their young? A predation-based hypothesis   /   Kerr, T.   Descamps, S.
(Canadian field-naturalist, v.122, no. 1, Jan.-Mar. 2008, p. 65-66)
(Kluane Red Squirrel Project contribution, no. 47)
References.
ASTIS record 77731.
Languages: English
Web: doi:10.22621/cfn.v122i1.546
Libraries: ACU

Our study reports the first observations consistent with Short-Tailed Weasel predation on juvenile North American Red Squirrels in the nest. Red Squirrel mothers are known to relocate their young to another nest after a disturbance. We suggest that this behaviour might be an efficient strategy that reduces the impact of litter depredation by weasels. (Au)


Energetic costs of male reproduction in a scramble competition mating system   /   Lane, J.E.   Boutin, S.   Speakman, J.R.   Humphries, M.M.
(Journal of animal ecology, v. 79, no. 1, Jan. 2010, p. 27-34, ill.)
(Kluane Red Squirrel Project contribution, no. 48)
References.
ASTIS record 73619.
Languages: English
Web: doi:10.1111/j.1365-2656.2009.01592.x
Libraries: ACU

Summary: 1. The assumption that the primary limitations on reproductive success differ between the sexes is inherent in traditional sexual selection theory. Although the energy that can be allocated to reproduction is assumed to be the main limitation to females, the ability to attract and defend oestrous females is assumed to be the primary limitation to males. 2. Estimates of the energetic costs of reproduction in male mammals are, however, limited and have largely been obtained from sexually dimorphic species exhibiting female defence mating systems. These studies often reveal that the energetic cost of male reproduction is similar to or even exceeds that of females, and therefore challenge long-held assumptions of inter-sexual reproductive limitations, but their generality is little known. 3. We coupled measurements of energy expenditure with detailed behavioural observations of reproductive male North American red squirrels (Tamiasciurus hudsonicus). This species displays minimal sexual dimorphism and exhibits a scramble competition mating system, under which sexual selection favours enhanced mate searching effort by males. 4. We conducted the study over 2 years characterized by a substantial variation in upcoming natural food availability and across two study populations that experienced either natural food abundance or an ad libitum food-supplementation to investigate the influence of resource availability on male reproductive energy expenditure. 5. Under natural conditions, mean energy expenditure of males across the 2 years was high, approximating that of females during lactation. Furthermore, in the anticipation of high upcoming natural food availability and resultant offspring survival, expenditure approximately doubled (from 290 ± 7 to 579 ± 73 kJ/day). When current food availability (and consequently the density of receptive females) was experimentally elevated, males displayed the highest levels of energy expenditure we recorded (873 ± 98 kJ/day). 6. Our results provide compelling evidence that the energy available for reproductive allocation places a strong limitation on reproduction in male North American red squirrels and contribute to previous work suggesting that high and limiting energetic costs of male reproduction may be a general feature of mammalian reproduction. (Au)


Quantitative methods for defining mast-seeding years across species and studies   /   LaMontagne, J.M.   Boutin, S.
(Journal of vegetation science, v. 20, no. 4, Aug. 2009, p. 745-753, ill.)
(Kluane Red Squirrel Project contribution, no. 49)
Appendices.
References.
ASTIS record 77732.
Languages: English
Web: doi:10.1111/j.1654-1103.2009.01068.x
Libraries: ACU

Although there is a quantitative method that is commonly used for identifying mast-seeding behaviour of a plant population based on the coefficient of variation (i.e. CV is standard deviation/mean>1), there is no general quantitative method for delineating “mast” as opposed to “non-mast” years. Mast years are, however, described qualitatively as years when “large”, “unusually large” and “high” seed production occurs. The use of a consistent and generally applicable method for delineating mast years across species and plant populations is important for synthesizing knowledge of the causes and consequences of mast seeding, which could be confounded by using different methods among studies. We examine six quantitative methods for identifying mast years: four methods from the literature and two methods developed here. We use 36 seed production datasets covering a variety of species with >=10 years of data to test the performance of these six methods. For each method, we quantify the percentage of the datasets to which the method could be successfully applied, the magnitude of the mast year relative to the mean, the frequency of mast years and the occurrence of consecutive mast years. The majority of the methods failed to meet the criteria for a suitable method. The best method used the number of standard deviates (standardized deviate method) of the annual mean seed production from the long-term mean of the dataset to identify mast-seeding years. General results from the standardized deviate method include that the occurrence of mast-seeding years is largely unrelated to plant population CV, but similar across species and data collection methods. (Au)


A predator's perspective of nest predation : predation by red squirrels is learned, not incidental   /   Pelech, S.A.   Smith, J.N.M.   Boutin, S.
(Oikos, v.119, no. 5, May 2010, p. 841-851, ill.)
(Kluane Red Squirrel Project contribution, no. 50)
References.
ASTIS record 77733.
Languages: English
Web: doi:10.1111/j.1600-0706.2009.17786.x
Libraries: ACU

Nest predation has been used to explain aspects of avian ecology ranging from nest site selection to population declines. Many arguments rely on specific assumptions regarding how predators find nests, yet these predatory mechanisms remain largely untested. Here we combine artificial nest experiments with behavioural observations of individual red squirrels Tamiasciurus hudsonicus to differentiate between two common hypotheses: predation is incidental versus learned. Specifically, we tested: 1) whether nest survival could be explained solely by a squirrel's activity patterns or habitat use, as predicted if predation was incidental; or 2) if predation increased as a squirrel gained experience preying on a nest, as predicted if predation was learned. We also monitored squirrel activity after predation to test for evidence of two search mechanisms: area-restricted searching and use of microhabitat search images. Contrary to incidental predation and in support of learning, squirrels did not find nests faster in areas with high use (e.g. forest edges). Instead, survival of artificial nests was strongly related to a squirrel's prior experience preying on artificial nests. Experience reduced nest survival times by over half and increased predation rates by 150–200%. Squirrels returned to and doubled their activity at the site of a previously preyed on nest. However, neither area-restricted searching nor microhabitat search images can explain how squirrels located artificial nests more readily with experience. Instead, squirrels likely used cues associated with the nests or eggs themselves. Learning implies that squirrels could be increasingly effective predators as the density or profitability of nests increases. Our results add support to the view that nest predation is complex and broadly influenced (e.g. by predator experience, motivation), and is unlikely to be predicted consistently by simple relationships with predator activity, abundance or habitat. (Au)


Associations between over-winter survival and resting metabolic rate in juvenile North American red squirrels   /   Larivée, M.L.   Boutin, S.   Speakman, J.R.   McAdam, A.G.   Humphries, M.M.
(Functional ecology, v. 24, no. 3, June 2010, p. 597-607, ill.)
(Kluane Red Squirrel Project contribution, no. 51)
References.
ASTIS record 73614.
Languages: English
Web: doi:10.1111/j.1365-2435.2009.01680.x
Libraries: ACU

Summary: 1. Resting metabolic rate (RMR) varies considerably among and within species. Two central questions in physiological ecology are whether values of RMR are repeatable and whether an association exists between RMR and fitness. 2. First, we investigated the repeatability of RMR in food hoarding, juvenile, North American red squirrels (Tamiasciurus hudsonicus Erxleben). Second, we explored links between RMR and survival. A low RMR may enhance survival if it reduces winter expenditure costs and/or allows more energy to be allocated towards autumn food hoarding. Alternately, a high RMR may enhance survival if it enables juveniles to hoard more food by increasing the throughput of energy available for investment in hoarding activities. 3. Resting metabolic rate adjusted for body mass, was repeatable in both males and females (r = 0·77) over a short-term (mean 24·3 days) but only among females (r = 0·72) over a long-term interval (mean 192 days). 4. Heavier juveniles and those with a lower RMR relative to their body mass were more likely to survive over-winter. Multiple selection models found significant selection for a decreased RMR (ß' = -0·56 ± 0·16) and increased mass (ß' = 0·69 ± 0·17). Survivors also tended to have more food stored within their hoard. 5. A low RMR relative to body mass and large body mass may have allowed individuals to minimize the expenditure costs related to a larger body mass, while maximizing thermal inertia. (Au)


Fecal cortisol metabolite levels in free-ranging North American red squirrels : assay validation and the effects of reproductive condition   /   Dantzer, B.   McAdam, A.G.   Palme, R.   Fletcher, Q.E.   Boutin, S.   Humphries, M.M.   Boonstra, R.
(General and comparative endocrinology, v.167, no. 2, 1 June 2010, p. 279-286, ill.)
(Kluane Red Squirrel Project contribution, no. 52)
Appendix of supplementary data available online.
References.
ASTIS record 73578.
Languages: English
Web: doi:10.1016/j.ygcen.2010.03.024
Libraries: ACU

Patterns in stress hormone (glucocorticoid: GC) levels and their relationship to reproductive condition in natural populations are rarely investigated. In this study, we (1) validate an enzyme-immunoassay to measure fecal cortisol metabolite (FCM) levels in North American red squirrels (Tamiasciurus hudsonicus), and (2) examine relationships between FCM levels and reproductive condition in a free-ranging red squirrel population. Injected radiolabeled cortisol was entirely metabolized and excreted in both the urine (mean ±SE; 70.3 ±0.02%) and feces (29.7 ±0.02%), with a lag time to peak excretion in the feces of 10.9 ±2.3 h. Our antibody reacted with several cortisol metabolites, and an adrenocorticotropic injection significantly increased FCM levels above baseline levels at 8 h post-injection. Relative to baseline levels, manipulation by handling also tended to increase FCM levels at 8 h post-manipulation, but this difference was not significant. FCM levels did not differ significantly between samples frozen immediately and 5 h after collection. Reproductive condition significantly affected FCM levels in free-ranging females (pregnant > lactating > post-lactating > non-breeding) but not males (scrotal testes vs. abdominal testes). Among females with known parturition dates, FCM levels increased during gestation, peaked at parturition, and declined during lactation. The difference between pregnant and lactating females was therefore dependent upon when the fecal samples were obtained during these periods, suggesting caution in categorizing reproductive stages. This study demonstrates the utility of fecal hormone metabolite assays to document patterns of glucocorticoid levels in free-ranging animals. (Au)


The functional response of a hoarding seed predator to mast seeding   /   Fletcher, Q.E.   Boutin, S.   Lane, J.E.   LaMontagne, J.M.   McAdam, A.G.   Krebs, C.J.   Humphries, M.M.
(Ecology, v. 91, no. 9, Sept. 2010, p.2673-2683, ill.)
(Kluane Red Squirrel Project contribution, no. 53)
Appendices.
References.
ASTIS record 77051.
Languages: English
Web: doi:10.1890/09-1816.1
Libraries: ACU

Mast seeding involves the episodic and synchronous production of large seed crops by perennial plants. The predator satiation hypothesis proposes that mast seeding maximizes seed escape because seed predators consume a decreasing proportion of available seeds with increasing seed production. However, the seed escape benefits of masting depend not only on whether predators are satiated at high levels of seed production, but also on the shape of their functional response (type II vs. type III), and the actual proportion of available seeds that they consume at different levels of seed production. North American red squirrels (Tamiasciurus hudsonicus) are the primary vertebrate predator of white spruce (Picea glauca) mast seed crops in many boreal regions because they hoard unopened cones in underground locations, preempting the normal sequence of cone opening, seed dispersal, and seed germination. We document the functional response of cone-hoarding by red squirrels across three non-mast years and one mast year by estimating the number of cones present in the territories of individual red squirrels and the proportion of these cones that they hoarded each autumn. Even though red squirrels are not constrained by the ingestive and on-body (fat reserves) energy reserve limitations experienced by animals that consume seeds directly, most squirrels hoarded < 10% of the cones present on their territories under mast conditions. Cone availability during non-mast years also reached levels that satiated the hoarding activity of red squirrels; however, this occurred only on the highest-quality territories. Squirrels switched to mushroom-hoarding when cone production was low and mushrooms were abundant. This resulted in type III functional response whereby the proportional harvest of cones was highest at levels of cone availability that were intermediate within non-mast years. Overall, more cones escaped squirrel cone-hoarding during a mast event than when cone production was low in non-mast years, which supports the predator satiation hypothesis. However, the highly variable seed escape in non-mast years may help to explain why all spruce cone production is not concentrated into fewer, larger, mast years. (Au)


Hippocampal neurogenesis in food-storing red squirrels : the impact of age and spatial behavior   /   Johnson, K.M.   Boonstra, R.   Wojtowicz, J.M.
(Genes, brain and behavior, v. 9, no. 6, Aug. 2010, p. 583-591, ill.)
(Kluane Red Squirrel Project contribution, no. 54)
Appendix.
References.
ASTIS record 77734.
Languages: English
Web: doi:10.1111/j.1601-183X.2010.00589.x
Libraries: ACU

The adaptive significance of adult hippocampal neurogenesis remains unknown. In the laboratory, it is influenced by a variety of environmental and physiological stimuli. In the wild, it may be influenced by the reliance on spatial memory and by environmental stressors. The one common denominator in both settings is that neurogenesis declines markedly with age. Red squirrels are long-lived rodents that store food (thousands of tree cones) to permit survival under harsh winter conditions. We compared a population from the eastern North America that stores its cones singly or in small clusters with one from the west that stores its cones in large stockpiles. The reliance on spatial memory should be much greater in the east than the west, and should not decline with age, as cone storage and recovery is a yearly necessity. We found no difference between the populations in the density of young neurons and both populations showed the same decline with age. Thus, we reject the spatial memory hypothesis for adult neurogenesis in mammals in its original form. Instead, our evidence is consistent with the neurogenic reserve hypothesis in which neuronal cell production early in life leads to enhanced hippocampal function later in life according to environmental demand but without requirement for ongoing cell production as a function of site- and species-specific needs. A more general interpretation of the data leads us to consider a possible role of neurogenesis in novel, flexible episodic memories. (Au)


Adopting kin enhances inclusive fitness in asocial red squirrels   /   Gorrell, J.C.   McAdam, A.G.   Coltman, D.W.   Humphries, M.M.   Boutin, S.
(Nature communications, v. 1, no. 22, 01 June 2010, p. 1-4, ill.)
(Kluane Red Squirrel Project contribution, no. 55)
References.
Available in paper and on the Web.
ASTIS record 73617.
Languages: English
Web: doi:10.1038/ncomms1022

Orphaned animals benefit from being adopted, but it is unclear why an adopting parent should incur the costs of rearing extra young. Such altruistic parental behaviour could be favoured if it is directed towards kin and the inclusive benefits of adoption exceed the costs. Here, we report the occurrence of adoption (five occurrences among 2,230 litters over 19 years) in asocial red squirrels (Tamiasciurus hudsonicus). Adoptions were always between kin, while orphans without nearby kin were never adopted. Adoptions were confined exclusively to circumstances in which the benefits to the adopted juvenile (b), discounted by the degree of relatedness between the surrogate and the orphan (r), exceeded the fitness costs of adding an extra juvenile to her litter (c), as predicted by Hamilton's rule (rb>c) for the evolution of altruism. By focusing on adoption in an asocial species, our study provides a clear test of Hamilton's rule that explains the persistence of occasional altruism in a natural mammal population. (Au)


Maternal androgens and behaviour in free-ranging North American red squirrels   /   Danzer, B.   McAdam, A.G.   Palme, R.   Humphries, M.M.   Boutin, S.   Boonstra, R.
(Animal behaviour, v. 81, no. 2, Feb. 2011, p. 469-479, ill.)
(Kluane Red Squirrel Project contribution, no. 56)
Appendices.
References.
ASTIS record 73580.
Languages: English
Web: doi:10.1016/j.anbehav.2010.11.021
Libraries: ACU

Variation in maternal behaviour can have profound consequences on offspring phenotype, survival, reproductive success, as well as maternal fitness. Understanding the mechanisms that underlie variation in maternal care can provide us with a more thorough understanding of the evolution of parental care. In some taxa, the effects of steroid hormones such as testosterone on paternal care have been well studied. However, patterns of female androgens in natural populations are rarely documented and relationships between maternal androgens and behaviour remain poorly studied. In this study, we first validated an enzyme immunoassay to measure faecal androgen metabolites (FAM) in territorial North American red squirrels, Tamiasciurus hudsonicus. We validated this assay by demonstrating that (1) our antibody reacts with testosterone metabolites, (2) reproductive females have significantly higher FAM than nonreproductive females, and (3) patterns of FAM were largely mirrored in plasma androgen levels. Second, we tested the hypothesis that androgen concentrations drive behavioural trade-offs in free-ranging breeding female red squirrels during gestation and lactation using 3 years of FAM data and 10 years of behavioural observations. FAM increased after conception and parturition, peaked during mid-lactation around the time of juvenile emergence, and then declined during the remainder of lactation and after weaning. Around the peak of FAM during mid-lactation, nest use was lowest, while territory defence and time spent foraging were at their highest levels. These associations between maternal androgens and behaviour support the hypothesis that androgens may play an important role in mediating maternal behaviour in free-ranging animals. (Au)


The heritability of multiple male mating in a promiscuous mammal   /   McFarlane, S.E.   Lane, J.E.   Taylor, R.W.   Gorrell, J.C.   Coltman, D.W.   Humphries, M.M.   Boutin, S.   McAdam, A.G.
(Biology letters, v. 7, no. 3, 23 June 2011, p. 368-371, ill.)
(Kluane Red Squirrel Project contribution, no. 57)
References.
ASTIS record 73618.
Languages: English
Web: doi:10.1098/rsbl.2010.1003
Libraries: ACU

The tendency of females to mate with multiple males is often explained by direct and indirect benefits that could outweigh the many potential costs of multiple mating. However, behaviour can only evolve in response to costs and benefits if there is sufficient genetic variation on which selection can act. We followed 108 mating chases of 85 North American red squirrels (Tamiasciurus hudsonicus) during 4 years, to measure each female's degree of multiple male mating (MMM), and used an animal model analysis of our multi-generational pedigree to provide what we believe is the first estimate of the heritability of MMM in the wild. Female red squirrels were highly polyandrous, mating with an average of 7.0 ± 0.2 males on their day of oestrus. Although we found evidence for moderate levels of additive genetic variation (CVA = 5.1), environmental variation was very high (CVE = 32.3), which resulted in a very low heritability estimate (h² < 0.01). So, while there is genetic variation in this trait, the large environmental variation suggests that any costs or benefits associated with differences among females in MMM are primarily owing to environmental and not genetic differences, which could constrain the evolutionary response to natural selection on this trait. (Au)


Intraspecific cache pilferage by larder-hoarding red squirrels (Tamiasciurus hudsonicus)   /   Donald, J.L.   Boutin, S.
(Journal of mammalogy, v. 92, no. 5, Oct. 2011, p.1013-1020, ill.)
(Kluane Red Squirrel Project contribution, no. 58)
References.
ASTIS record 77025.
Languages: English
Web: doi:10.1644/10-MAMM-A-340.1
Libraries: ACU

Although cases of pilfering food are reported commonly in the mammal literature, the factors affecting pilfering rates among individuals and between populations within the same species remain relatively unknown. We measured individual pilfering rates in 2 populations of highly territorial larder-hoarding red squirrels (Tamiasciurus hudsonicus) in Kluane, Yukon, Canada. One population received artificial food supplementation (where all individuals had ad libitum food) and had a 2-fold higher density than the control population. We knew the age, relatedness, and spatial relationship of all individuals in each population, and we had a measure of the food resources (cones) cached by each individual and their fates through the study. Results from experimental removal of territory owners suggested that younger squirrels with smaller food caches were more likely to pilfer when provided the opportunity. However, using a mark–recapture study of marked spruce cones under natural conditions, we found that few individuals (14%) pilfered, and stolen cones represented only 0.3% of total cones that were larder-hoarded. Pilfering occurs at a much lower rate in Kluane than reported for red squirrels in other regions and is less than rates reported for scatter-hoarding species. (Au)


How does diet affect fecal steroid hormone metabolite concentrations? An experimental examination in red squirrels   /   Dantzer, B.   McAdam, A.G.   Palme, R.   Boutin, S.   Boonstra, R.
(General and comparative endocrinology, v.174, no. 2, 1 Nov. 2011, p. 124-131, ill.)
(Kluane Red Squirrel Project contribution, no. 59)
Appendix.
References.
ASTIS record 77728.
Languages: English
Web: doi:10.1016/j.ygcen.2011.08.010
Libraries: ACU

A growing number of longitudinal studies in free-ranging animals are measuring fecal steroid hormone metabolite concentrations (FHM). Free-ranging animals can exhibit major seasonal changes in their diet, yet we know relatively little about how diet affects FHM. We experimentally manipulated the diets of female and male North American red squirrels (Tamiasciurus hudsonicus) to determine how diet affected fecal cortisol (FCM) and androgen (FAM) metabolite concentrations. We measured FCM using an enzyme immunoassay (EIA) that we have previously validated and measured FAM using an assay we have previously validated for use in females and validate for males herein. We validated our EIA to measure FAM in males by identifying that 44.5 ± 0.05% of recovered radiolabeled testosterone was excreted in the feces, our EIA antibody detected the fecal testosterone metabolites, and males with scrotal testes had significantly higher FAM (3.02 ± 0.06 ln ng/g dry feces) than those with abdominal testes (2.73 ± 0.06). We initially fed all squirrels the same diet, but then switched one group of squirrels to a diet consisting of conifer seed (n = 4 squirrels) whereas the other group was switched to peanut butter (n = 7). FCM and FAM in squirrels fed conifer seed significantly increased from 0 to 94 h after their diets were changed. FCM in squirrels fed peanut butter significantly declined, whereas FAM declined but not significantly. This demonstrates that change in dietary fiber consumption (peanut butter versus conifer seed) or even slight differences in diet (conifer versus sunflower seeds) can strongly influence FHM. (Au)


Behavioral responses of territorial red squirrels to natural and experimental variation in population density   /   Dantzer, B.   Boutin, S.   Humphries, M.M.   McAdam, A.G.
(Behavioral ecology and sociobiology, v. 66, no. 6, June 2012, p. 865-878, ill.)
(Kluane Red Squirrel Project contribution, no. 60)
References.
ASTIS record 77726.
Languages: English
Web: doi:10.1007/s00265-012-1335-2
Libraries: ACU

The relative scarcity of studies at the intersection of behavioral and population ecology is surprising given the presumed importance of behavior in density-dependent population regulation. Here we tested whether North American red squirrels (Tamiasciurus hudsonicus) adjust their behavior in response to local population density and whether they use rates of territorial vocalizations in their local neighborhood to assess density. We examined these relationships using 18 years of live trapping and 20 years of behavioral data that were collected across natural variation in local population density. To disentangle the effects of population density on behavior from those due to changes in per capita food abundance or changes in the frequency of antagonistic interactions with neighbors, we also experimentally manipulated population density with long-term food supplementation as well as perceived population density with longterm playbacks of territorial vocalizations. The frequency with which squirrels emitted territorial vocalizations was positively associated with local population density. In contrast, antagonistic physical interactions observed between squirrels and territorial intrusions were rare and the frequency of intrusions was weakly and negatively, not positively, associated with population density. Squirrels experiencing naturally and experimentally high density conditions spent less time in the nest and feeding but more time being vigilant. Similar density-dependent changes in behavior were observed in response to our manipulations of perceived population density, indicating that vocalization rates and not physical interactions or food abundance were the mechanism by which squirrels assessed and responded behaviorally to changes in local density. (Au)


Within-season synchrony of a masting conifer enhances seed escape   /   Archibald, D.W.   McAdam, A.G.   Boutin, S.   Fletcher, Q.E.   Humphries, M.M.
(American naturalist, v.179, no. 4, Apr. 2012, p. 536-544, ill.)
(Kluane Red Squirrel Project contribution, no. 61)
References.
ASTIS record 77724.
Languages: English
Web: doi:10.1086/664623
Libraries: ACU

Predator satiation resulting from interannual reproductive synchrony has been widely documented in masting plants, but how reproductive synchrony within a year influences seed escape is poorly understood. We evaluated whether the intra-annual reproductive synchrony of individual white spruce trees (Picea glauca) increased seed escape from their primary predispersal seed predator, North American red squirrels (Tamiasciurus hudsonicus). Trees with cones that matured synchronously relative to those of other trees within red squirrel territories were significantly more likely to escape squirrel predation in years with both low and superabundant levels of cone production, generating a significantly positive linear selection differential for increasing intra-annual reproductive synchrony. Thus, this masting plant escapes seed predation in numbers through interannual synchrony in seed production and in time through intra-annual synchrony of seed availability. (Au)


Low heritabilities, but genetic and maternal correlations between red squirrel behaviours   /   Taylor, R.W.   Boon, A.K.   Dantzer, B.   Réale, D.   Humphries, M.M.   Boutin, S.   Gorrell, J.C.   Coltman, D.W.   McAdam, A.G.
(Journal of evolutionary biology, v. 25, no. 4, Apr. 2012, p. 614-624)
(Kluane Red Squirrel Project contribution, no. 62)
Appendices.
References.
ASTIS record 77722.
Languages: English
Web: doi:10.1111/j.1420-9101.2012.02456.x
Libraries: ACU

Consistent individual differences in behaviour, and behavioural correlations within and across contexts, are referred to as animal personalities. These patterns of variation have been identified in many animal taxa and are likely to have important ecological and evolutionary consequences. Despite their importance, genetic and environmental sources of variation in personalities have rarely been characterized in wild populations. We used a Bayesian animal model approach to estimate genetic parameters for aggression, activity and docility in North American red squirrels (Tamiasciurus hudsonicus). We found support for low heritabilities (0.08-0.12), and cohort effects (0.07-0.09), as well as low to moderate maternal effects (0.07-0.15) and permanent environmental effects (0.08-0.16). Finally, we found evidence of a substantial positive genetic correlation (0.68) and maternal effects correlation (0.58) between activity and aggression providing evidence of genetically based behavioural correlations in red squirrels. These results provide evidence for the presence of heritable variation in red squirrel behaviour, but also emphasize the role of other sources of variation, including maternal effects, in shaping patterns of variation and covariation in behavioural traits. (Au)


Territorial defence behaviour in red squirrels is influenced by local density   /   Shonfield, J.   Taylor, R.W.   Boutin, S.   Humphries, M.M.   McAdam, A.G.
(Behaviour, v.149, no. 3/4, 2012, p. 369-390, ill.)
(Kluane Red Squirrel Project contribution, no. 63)
References.
ASTIS record 77720.
Languages: English
Web: doi:10.1163/156853912X637842
Libraries: ACU

While many animals defend territories to secure resources such as food and mates, little is known about why territory owners of the same species vary in their territorial defence behaviour. We tested whether potential intruder pressure, defence of offspring, resource-holding potential or aggressiveness of the individual territory owner best explained intraspecific differences in territorial defence in a wild population of North American red squirrels (Tamiasciurus hudsonicus). We assessed territorial defence behaviour of individual red squirrels by recording whether or not they produced territorial vocalizations, known as rattles, both in response to a territorial playback and during natural observation sessions without an experimental stimulus. We compared the relative fit of four a priori models to explain territorial defence intensity in red squirrels and found that rattling behaviour in red squirrels under natural conditions was best explained by the intruder pressure hypothesis. Red squirrels were more likely to vocalize if they were surrounded by a higher density of conspecifics on neighbouring territories, indicating that they adjust territorial defence in response to potential intruder pressure. However, vocalization responses of red squirrels to the playback were not affected by local density, which was reflected in similar support for the four a priori models. The differing effects of local density on red squirrel vocalization rate during natural observations and following playbacks indicates that the effects of local density on the territorial behaviour of red squirrels depends on the particular context in which this behaviour is expressed. (Au)


Sexing the Sciuridae : a simple and accurate set of molecular methods to determine sex in tree squirrels, ground squirrels and marmots   /   Gorrell, J.C.   Boutin, S.   Raveh, S.   Neuhaus, P.   Côté, S.D.   Coltman, D.W.
(Molecular ecology resources, v. 12, no. 5, Sept. 2012, p. 806-809, ill.)
(Kluane Red Squirrel Project contribution, no. 64)
References.
ASTIS record 77719.
Languages: English
Web: doi:10.1111/j.1755-0998.2012.03165.x
Libraries: ACU

We determined the sequence of the male-specific minor histocompatibility complex antigen (Smcy) from the Y chromosome of seven squirrel species (Sciuridae, Rodentia). Based on conserved regions inside the Smcy intron sequence, we designed PCR primers for sex determination in these species that can be co-amplified with nuclear loci as controls. PCR co-amplification yields two products for males and one for females that are easily visualized as bands by agarose gel electrophoresis. Our method provides simple and reliable sex determination across a wide range of squirrel species. (Au)


Seasonal stage differences overwhelm environmental and individual factors as determinants of energy expenditure in free-ranging red squirrels   /   Fletcher, Q.E.   Speakman, J.R.   Boutin, S.   McAdam, A.G.   Woods, S.B.   Humphries, M.M.
(Functional ecology, v. 26, no. 3, June 2012, p. 677-687, ill.)
(Kluane Red Squirrel Project contribution, no. 65)
Appendices.
References.
ASTIS record 77715.
Languages: English
Web: doi:10.1111/j.1365-2435.2012.01975.x
Libraries: ACU

Summary: 1. Despite the central importance of the rate of energy expenditure in the lives of animals, the major drivers of within-species variation in energy expenditure remain uncertain, largely because most intraspecific studies focus on one or only a few potential determinants of expenditure. 2. Here, we examine the determinants of daily energy expenditure (DEE) in free-ranging female North American red squirrels (Tamiasciurus hudsonicus Erxleben) occupying a highly seasonal environment. By relating variation in 260 measurements of DEE from 176 individuals to key sources of seasonal (reproductive and foraging stages), environmental (resources and air temperature) and individual (body mass and individual identity) variation, our comprehensive analysis examines the relative importance of DEE predictors that have been more commonly examined in isolation. 3. Red squirrels demonstrated extensive variation in DEE with 5th (177 kJ per day) and 95th (660 kJ per day) percentile DEE levels that would correspond to mammals on an interspecific scale ranging in mass from 148 to 1120 g. 4. Seasonal stage differences accounted for most variation in DEE, with high expenditure during lactation and autumn hoarding, and very low expenditure during winter. Contrary to interspecific studies, energy expenditure increased with increasing ambient temperature and it was weakly related to body mass in all seasons except for winter. High resource availability was associated with reduced energy expenditure in winter, but elevated expenditure during lactation and hoarding. 5. Collectively, these results highlight substantial intraspecific variation in energy expenditure, most of which can be explained by a combination of seasonal stages and environmental conditions, and fundamental differences in the importance and direction of determinants of energy expenditure when examined at the intra- versus the interspecific level. (Au)


Oxidative damage increases with reproductive energy expenditure and is reduced by food-supplementation   /   Fletcher, Q.E.   Selman, C.   Boutin, S.   McAdam, A.G.   Woods, S.B.   Seo, A.Y.   Leeuwenburgh, C.   Speakman, J.R.   Humphries, M.M.
(Evolution, v. 67, no. 5, May 2013, p.1527-1536, ill.)
(Kluane Red Squirrel Project contribution, no. 66)
References.
ASTIS record 77713.
Languages: English
Web: doi:10.1111/evo.12014
Libraries: ACU

A central principle in life-history theory is that reproductive effort negatively affects survival. Costs of reproduction are thought to be physiologically based, but the underlying mechanisms remain poorly understood. Using female North American red squirrels (Tamiasciurus hudsonicus), we test the hypothesis that energetic investment in reproduction overwhelms investment in antioxidant protection, leading to oxidative damage. In support of this hypothesis we found that the highest levels of plasma protein oxidative damage in squirrels occurred during the energetically demanding period of lactation. Moreover, plasma protein oxidative damage was also elevated in squirrels that expended the most energy and had the lowest antioxidant protection. Finally, we found that squirrels that were food-supplemented during lactation and winter had increased antioxidant protection and reduced plasma protein oxidative damage providing the first experimental evidence in the wild that access to abundant resources can reduce this physiological cost. (Au)


Communal nesting in an 'asocial' mammal : social thermoregulation among spatially dispersed kin   /   Williams, C.T.   Gorrell, J.C.   Lane, J.E.   McAdam, A.G.   Humphries, M.M.   Boutin, S.
(Behavioral ecology and sociobiology, v. 67, no. 5, May 2013, p. 757-763, ill.)
(Kluane Red Squirrel Project contribution, no. 67)
References.
ASTIS record 77711.
Languages: English
Web: doi:10.1007/s00265-013-1499-4
Libraries: ACU

Communal nesting can help defray the high cost of endothermic heat production in cold environments, but such social behavior is generally thought to be incompatible with the persistent defense of exclusive territories in typically ‘asocial’ animals. We examined the propensity for communal nesting in female red squirrels (Tamiasciurus hudsonicus), which maintain individual year-round territories, through intensive monitoring of litters over 22 years and by radio-tracking females during 3 years in late winter/-early spring. Communal nesting was exceptionally rare during lactation: of 1,381 litters tracked to emergence, we observed a single instance in which two closely related (r=0.5) females pooled their litters into a single nest. In contrast, nest sharing between 2–3 females was relatively common in the late winter/early spring, prior to mating; at least 12 of 63 females (19 %) engaged in communal nesting during a year of systematic tracking of radio-collared females from late February to April. Communal nesting occurred more frequently when temperatures were colder, suggesting that such aggregations might function to reduce thermoregulatory costs. These social associations were typically, though not exclusively, between closely related individuals (r=>0.25 for seven of eight cases; mother-daughter dyads: four of eight), suggesting this cooperative behavior might evolve through kin selection and/or may reflect extended parental care. Our results demonstrate that female red squirrels engage in communal nesting, typically with closely related kin, despite a dispersed population structure that stems from the persistent defense of individual territories. (Au)


Density triggers maternal hormones that increase adaptive offspring growth in a wild mammal   /   Dantzer, B.   Newman, A.E.M.   Boonstra, R.   Palme, R.   Boutin, S.   Humphries, M.M.   McAdam, A.G.
(Science, v.340, no.6137, 7 June 2013, p.1215-1217)
(Kluane Red Squirrel Project contribution, no. 69)
References.
ASTIS record 77708.
Languages: English
Web: doi:10.1126/science.1235765
Libraries: ACU

In fluctuating environments, mothers may enhance the fitness of their offspring by adjusting offspring phenotypes to match the environment they will experience at independence. In free-ranging red squirrels, natural selection on offspring postnatal growth rates varies according to population density, with selection favoring faster-growing offspring under high-density conditions. We show that exposing mothers to high-density cues, accomplished via playbacks of territorial vocalizations, led to increased offspring growth rates in the absence of additional food resources. Experimental elevation of actual and perceived density induced higher maternal glucocorticoid levels, and females with naturally or experimentally increased glucocorticoids produced offspring that grew faster than controls. Social cues reflecting population density were, therefore, sufficient to elicit increased offspring growth through an adaptive hormone-mediated maternal effect. (Au)


Red squirrels use territorial vocalizations for kin discrimination   /   Wilson, D.R.   Goble, A.R.   Boutin, S.   Humphries, M.M.   Coltman, D.W.   Gorrell, J.C.   Shonfield, J.   McAdam, A.G.
(Animal behaviour, v.107, Sept. 2015, p. 79-85, ill. )
(Kluane Red Squirrel Project contribution, no. 81)
References.
ASTIS record 82100.
Languages: English
Web: doi:10.1016/j.anbehav.2015.06.011
Libraries: ACU

The ability to discriminate among individuals, or among classes of individuals, can provide animals with important fitness benefits. Although several mechanisms for discrimination are possible, most require animals to show stable phenotypic variation that reflects their identity or their membership in a particular class (e.g. sex, mate, kin). For territorial animals that rarely interact physically, vocalizations could serve as long-distance signals that facilitate discrimination. In this study, we tested whether the territorial rattle vocalizations of North American red squirrels, Tamiasciurus hudsonicus, are repeatable, and whether they could hence provide the basis for multiple types of discrimination. We measured four structural features from two rattles from each of 76 marked squirrels. All four features were repeatable, which is consistent with territorial rattles being individually distinctive. We then conducted a playback experiment to determine whether squirrels use rattles for discrimination. Specifically, we tested whether squirrels discriminate between the rattles of neighbours and non-neighbours, and kin (coefficient of relatedness, r >= 0.25) and non-kin (r < 0.125). Following a 2 × 2 factorial design, we broadcast a rattle from a non-neighbouring nonkin individual to 15 subjects, from a neighbouring nonkin individual to 14 subjects, from a non-neighbouring kin individual to 11 subjects, and from a neighbouring kin individual to 13 subjects. Subjects did not discriminate between the rattles of neighbours and non-neighbours, but did respond differently to the rattles of kin and nonkin. Specifically, squirrels were significantly more likely to produce a rattle of their own in response to the broadcasted rattles of nonkin versus the broadcasted rattles of kin. This result demonstrates that red squirrels can use territorial vocalizations for kin discrimination. It also suggests that they are more tolerant of territorial intrusions by kin. (Au)


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