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Early-life adversity, even when transient, can have lasting effects on individual phenotypes and reduce lifespan across species. If these effects can be mitigated by a high-quality later-life environment, then differences in future resources may explain variable resilience to early-life adversity. Using data from over 1000 wild North American red squirrels, we tested the hypothesis that the costs of early-life adversity for adult lifespan could be offset by later-life food abundance. We identified six adversities that reduced juvenile survival in the first year of life, though only one—birth date—had continued independent effects on adult lifespan. We then built a weighted early-life adversity (wELA) index integrating the sum of adversities and their effect sizes. Greater weighted early-life adversity predicted shorter adult lifespans in males and females, but a naturally occurring food boom in the second year of life ameliorated this effect. Experimental food supplementation did not replicate this pattern, despite increasing lifespan, indicating that the buffering effect of a future food boom may hinge on more than an increase in available calories. Our results suggest a non-deterministic role of early-life conditions for later-life phenotype, highlighting the importance of evaluating the consequences of early-life adversity in the context of an animal's entire life course. [ABSTRACT FROM AUTHOR]

Territories are typically defined as spatially exclusive areas that are defended against conspecifics. Given the spatial nature of territoriality, it is inherently density dependent, but the economics of territoriality also depend on the distribution and abundance of defended resources. Our objectives were to assess the effects of changing population density and food availability on individually based territorial phenotypes.We developed a novel analytical framework that bridges spatially explicit territories with social network analysis to model density‐dependent territorial phenotypes. Using the outputs from our data pipeline, we modelled plasticity in territory size and territory intrusion rates in a long‐term study population of North American red squirrels Tamiasciurus hudsonicus. Red squirrels defend year‐round territories around a central hoard (midden) of white spruce Picea glauca cones. Importantly, white spruce is a masting species that produces large cone crops every 4–7 years (i.e. mast years) in our study area interspersed with non‐mast years when few cones are produced. In the spring following mast years, populations are approximately double in size, but are lower in the spring of non‐mast years.We predicted that territory size and intrusion rates would decrease as resource abundance, and consequently population density, increased. By contrast, as resource abundance decreased via depletion, and therefore density decreased, territories should increase in size and intrusions should also increase.As we expected, individual territory size and territorial intrusions were negatively density dependent, such that increased density after mast years resulted in smaller territories and fewer intrusions. When considering between‐individual variation in plasticity across a density gradient, individuals responded differently to changes in population density within their lifetime.Our results show that territory size and intrusion rates display negative density dependence. When food becomes available in the autumn of a mast year and density in spring of the following year increases, territories shrink in size to effectively a small area around the midden. While our findings for red squirrels are unique compared to other systems, they serve as a reminder that the direction and strength of fundamental ecological relationships can depend on the nature of the system. [ABSTRACT FROM AUTHOR]

The most commonly reported ecological effects of climate change are shifts in phenologies, in particular of warmer spring temperatures leading to earlier timing of key events (1,2). Among animals, however, [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.10.038 Byline: Jeffrey E. Lane, Stan Boutin, Melissa R. Gunn, Jon Slate, David W. Coltman Abstract: 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. Author Affiliation: (a) Department of Biological Sciences, University of Alberta, Edmonton, Canada (a ) Central Science Laboratory, Woodchester Park, U.K. (a ) Department of Animal and Plant Sciences, University of Sheffield, U.K. Article History: Received 8 August 2007; Revised 29 August 2007; Accepted 31 October 2007 Article Note: (miscellaneous) MS. number: A10842

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2006.12.017 Byline: Jeffrey E. Lane, Stan Boutin, Melissa R. Gunn, Jon Slate, David W. Coltman Abstract: 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. Author Affiliation: (a) Department of Biological Sciences, University of Alberta, Edmonton, Canada (a ) Department of Animal and Plant Sciences, University of Sheffield, U.K. Article History: Received 4 October 2006; Revised 9 November 2006; Accepted 26 December 2006 Article Note: (miscellaneous) MS. number: A10581R