In animals, physiological mechanisms underlying reproductive and actuarial senescence remain poorly understood. Immunosenescence, the decline in the ability to display an efficient immune response with increasing age, is likely to influence both reproductive and actuarial senescence through increased risk of disease. Evidence for such a link has been reported from laboratory animal models but has been poorly investigated in the wild, where variation in resource acquisitions usually drives life-history trade-offs. We investigated immunosenescence patterns over 7 years in both sexes of two contrasting roe deer populations (Capreolus capreolus). We first measured twelve immune markers to obtain a thorough identification of innate and adaptive components of immunity and assessed, from the same individuals, the age-dependent variation observed in parasitic infections. Although the level of innate traits was maintained at old age, the functional innate immune traits declined with increasing age in one of two populations. In both populations, the production of inflammatory markers increased with advancing age. Finally, the adaptive response declined in late adulthood. The increasing parasite burden with age we reported suggests the effective existence of immunosenescence. Age-specific patterns differed between populations but not between sexes, which indicate that habitat quality could shape age-dependent immune phenotype in the wild.

Individual body mass often positively correlates with survival and reproductive success, whereas fitness costs of growing large are rarely detected in vertebrates in the wild. Evidence that adult body mass progressively declines with increasing age is accumulating across mammalian populations. Growing fast to a large body can increase the cellular damage accumulated throughout life, leading body growth in early life to be negatively associated with the rate of body mass senescence. Moreover, the onset of mass senescence may strongly depend on both sex‐specific reproductive tactics and environmental conditions. Assessing the timing and the rate of body mass decline with increasing age thus offers an opportunity to look for costs of having grown fast, especially after a poor start during early life, in both sexes and in different environments. Using a unique dataset including 30 years of longitudinal data on age‐specific body mass collected in two roe deer Capreolus capreolus populations subjected to contrasted environmental conditions, we looked for potential costs of high post‐weaning growth rate in terms of steeper rate of body mass senescence. Our analyses of body mass senescence accounted for the potential variation in the onset of senescence and allowed explicit comparisons of this variable between sexes and populations. Higher growth rates late in the growing period (after weaning) were associated with a steeper rate of body mass senescence, regardless of early mass (gained before weaning), but at different extents depending on sex and environmental conditions. Body mass senescence occurred earlier in males than in females, especially in the population facing limiting resources. In the wild, although heavy individuals generally survive better than small ones, the costs of growing large late in the growing period only became apparent late in life through mass senescence.

Data on 22 radio-collared adult female roe deer Capreolus capreolus in the Chizé forest were used to test whether their home-range size was influenced by resource availability and reproductive status. As roe deer females are income breeders and invest heavily in each reproductive attempt, they should be limited by energetic constraints. Thus it was expected that: (1) heavier females should have larger home ranges; (2) that home-range size should decrease with increasing vegetation biomass; (3) home-range size should increase with increasing reproductive effort (i.e. females with two fawns at heel should have larger home ranges than those with one fawn, which should have larger home range than females without fawns). To test these predictions, variation in spring-summer homerange size was studied in 2001 and 2002, using 95% kernel home-range estimation. Results showed that females do not adjust their home-range size in response to body mass or age. Home-range size increased with increasing reproductive success, but the magnitude of the change varied over the period of maternal care. Finally, although their home-range size decreased with increasing plant biomass (slope = − 0.11, SE = 0.065), female roe deer at Chizé did not fully compensate for declines in food availability by increasing home-range size.

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