Rural populations of the red fox Vulpes vulpes show little evidence of reproductive senescence
Résumé
The ageing theory predicts fast and early senescence for fast-living species. We investigated whether the pattern of senescence of a medium-
sized, fast-living and heavily-culled mammal, the red fox (Vulpes vulpes), fits this theoretical prediction. We used cross-sectional data from a
large-scale culling experiment of red fox conducted over six years in five study sites located in two regions of France to explore the age-related
variation in reproductive output. We used both placental scars and embryos counts from 755 vixens’ carcasses aged by the tooth cementum method (age range : 1-10) , as proxies for litter size. Mean litter size per vixen was 4.7 ± 1.4. Results from Generalized Additive Mixed Models revealed a significant variation of litter size with age. Litter size peaked at age 4 with 5. 0 ± 0.2 placental scars and decreased there after by
0.5 cubs per year. Interestingly, we found a different age-specific variation when counting embryos which reached a plateau at age 5-6 (5.5 ± 0.2)
and decreased slower than placent al scars across older ages, pointing out embryo resorption as a potential physiological mechanism of reproductive senescence in the red fox. Contrary to our expectation, reproductive senescence is weak, occurs late in life and takes place at an age reached by less than 11.7% of the population such that very few females exhibit senescence in these heavily culled populations
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