Age-specific variation in survival, reproductive success and offspring quality in red squirrels: evidence of senescence

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.