Browsing by Author "McAdam, Andrew G."
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Item Fitness consequences of peak reproductive effort in a resource pulse system(2017) Hämäläinen, Anni; McAdam, Andrew G.; Dantzer, Ben; Lane, Jeffrey E.; Haines, Jessica A.; Humphries, Murray M.; Boutin, StanThe age trajectory of reproductive performance of many iteroparous species features an early - life increase in performance followed by a late - life senescent decline. The largest contribution of lifetime reproductive success is therefore gained at the age at which reproductive performance peaks. Using long term data on North American red squirrels we show that the environmental conditions individuals encountered could cause variation among individuals in the “height” and timing of this peak, contributing to life history variation and fitness in this population that experiences irregular resource pulses. As expected, high peak effort was positively associated with lifetime reproductive output up to a high level of annual effort. Furthermore, individuals that matched their peak reproductive effort to an anticipated resource pulse gained substantial fitness benefits through recruiting more offspring over their lifetime. Individual variation in peak reproductive effort thus has strong potential to shape life history evolution by facilitating adaptation to fluctuating environments.Item Indirect effects on fitness between individuals that have never met via an extended phenotype(2019) Fisher, David N.; Haines, Jessica A.; Boutin, Stan; Dantzer, Ben; Lane, Jeffrey E.; Coltman, David W.; McAdam, Andrew G.Interactions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes that alter the environments others experience. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically outlives the individual and is usually subsequently acquired by non-relatives. Hoarding by previous owners can, therefore, influence subsequent owners. We found that red squirrels breed earlier and had higher lifetime fitness if the previous hoard owner was a male. This was driven by hoarding behaviour, as males and mid-aged squirrels had the largest hoards, and these effects persisted across owners, such that if the previous owner was male or died in mid-age, subsequent occupants had larger hoards. Individuals can, therefore, influence each other's resource-dependent traits and fitness without ever meeting, such that the past can influence contemporary population dynamics through extended phenotypes.Item Sex- and context-specific associations between personality and a measure of fitness but no link with life history traits(2020) Haines, Jessica A.; Nason, Sarah E.; Skurdal, Alyshia M. M.; Bourchier, Tenal; Boutin, Stan; Taylor, Ryan W.; McAdam, Andrew G.; Lane, Jeffrey E.; Kelley, Amanda D.; Humphries, Murray M.The pace-of-life syndrome hypothesis posits that personality traits (i.e. consistent individual differences in behaviour) are linked to life history and fitness. Specifically, fast-paced individuals are predicted to be proactive (i.e. active and aggressive) with an earlier age at first reproduction, a shorter life span and higher fecundity than slow-paced individuals. Environmental conditions and sex differences may be important in maintaining behavioural and life history variation in populations and may influence the covariance of personality with life history or lifetime fitness. However, these effects are rarely tested together. We investigated whether the occurrence of a resource pulse (called a mast year) during adulthood altered the associations between personality and life history traits or lifetime offspring production in adult North American red squirrels, Tamiasciurus hudsonicus. Despite accounting for environmental context during adulthood, we found no evidence of an overall pace-of-life syndrome in this population as personality was not associated with age at first reproduction or longevity in either sex. Males and females had similar activity levels, but females were more aggressive, potentially due to the fitness benefits of protecting their offspring from predation. In all females, regardless of mast experience, there was no association between activity and lifetime pup production, but there was a positive association between aggression and lifetime pup production. In males that experienced a mast, there was a positive association between lifetime pup production and both activity and aggression. In males that did not experience a mast, there was no association between activity and lifetime pup production, but there was a negative association between aggression and lifetime pup production. Lifetime recruit production (number of adult offspring recruited into the breeding population) in either sex was not influenced by activity or aggression regardless of mast experience. Overall, our results suggest that the infrequent occurrence of mast years may contribute to maintaining variation in personality traits in red squirrels.Item Sex-specific effects of capital resources on reproductive timing and success in red squirrels(2022) Haines, Jessica A.; Delaney, David M.; Wishart, Andrea E.; McAdam, Andrew G.; Coltman, David W.; Lane, Jeffrey E.; Dantzer, Ben; Boutin, StanReproduction is an energetically expensive activity for both sexes. However, if males and females differ in their annual timing of reproduction, such that peak investment for one sex occurs during a more resource-limited period, there is an opportunity for sex-specific selection to act on the acquisition of energetic resources. Both male and female North American red squirrels (Tamiasciurus hudsonicus) cache conifer cones, although males typically have larger caches than females. Peak energetic investment in reproduction occurs for males during the mating season in winter and early spring (when squirrels rely almost exclusively on cached resources) and for females during lactation (which can align with fresh food availability). We provide evidence that suggests sex differences in cache size are likely driven by a stronger positive connection between cached resources and components of fitness for males than for females. Specifically, males with larger caches have greater siring success than males with smaller caches, whereas for females, only early breeding females experience a positive effect of cache size on the number of recruits produced. We also show that males sire pups and females give birth earlier in the year if they have larger caches compared with squirrels of the same sex with smaller caches. Sexual selection can thus extend beyond traits directly connected to mating behavior, and can act on traits related to acquiring resources needed to fuel reproduction that are expressed months or years in advance of breeding efforts.Item Sexually selected infanticide by male red squirrels in advance of a mast year(2018) Haines, Jessica A.; Coltman, David W.; Dantzer, Ben; Gorrell, Jamieson C.; Humphries, Murray M.; Lane, Jeffrey E.; McAdam, Andrew G.; Boutin, StanNorth American red squirrels (Tamiasciurus hudsonicus) anticipate when white spruce (Picea glauca), their primary food source, will produce large amounts of cones in infrequent and irregular mast years (Boutin et al. 2006). Cones mature in autumn and are then available as food for red squirrels, but females produce larger, and often multiple, litters the preceding spring and summer in anticipation of the upcoming mast. Because this pulse of the cone food resource follows the birth of the litter, it cannot be a source of energy for the female to produce young; instead, there must be cues for increased reproductive investment by the females prior to mast cone production, perhaps through consumption of buds on the masting trees (Boutin et al. 2006, 2013). Boutin et al. (2006) only studied females; whether male behavior anticipates mast years is still unstudied. At our study area in the Yukon, 2014 was a mast year for spruce cone production in late summer (Lamontagne et al. 2005). J. A. Haines was observing male red squirrel mating behavior during spring 2014, giving her an unanticipated opportunity to document the previously unstudied effects of a mast year on male red squirrels.