Under life‐history theories of ageing, increased senescence should follow relatively high reproductive effort. This expectation has rarely been tested against senescence varying between and within the two sexes, although such an approach may clarify the origins of sex‐specific ageing in the context of a given mating system. Nazca boobies ( Longitudinal data were used to (a) evaluate the sex specificity of reproductive and actuarial senescence and then (b) test for early‐/late‐life fitness trade‐offs within each sex. Within‐sex analyses inform an interpretation of sex differences in senescence based on costs of reproduction. Analyses incorporated individual heterogeneity in breeding performance and cohort‐level differences in early‐adult environments. Females showed marginally more intense actuarial senescence and stronger age‐related declines for fledging success. The opposite pattern (earlier and faster male senescence) was found for breeding probability. Individual reproductive effort in early life positively predicted late‐life reproductive performance in both sexes and thus did not support a causal link between early‐reproduction/late‐life fitness trade‐offs and sex differences in ageing. A high‐quality diet in early adulthood reduced late‐life survival (females) and accelerated senescence for fledging success (males). This study documents clear variation in ageing patterns—by sex, early‐adult environment and early‐adult reproductive effort—with implications for the role mating systems and early‐life environments play in determining ageing patterns. Absent evidence for a disposable soma mechanism, patterns of sex differences in senescence may result from age‐ and condition‐dependent mate choice interacting with this population's male‐biased sex ratio and mate rotation.
Age‐related variation in reproductive performance in long‐lived iteroparous vertebrate species is common, with performance being influenced by within‐individual processes, such as improvement and senescence, in combination with among‐individual processes, such as selective appearance and disappearance. Few studies of age‐related reproductive performance have compared the role of these drivers within a metapopulation, subject to varying degrees of resource competition. We accounted for within‐ and among‐individual changes among known‐aged Adélie penguins Age at first reproduction (AFR) was lowest, and number of breeding attempts highest, at the largest colony. Regardless of AFR, success improved with early post‐recruitment experience. For both oldest and youngest recruitment groups, peak performance occurred at the end of their reproductive life span indicating a possible cost of reproduction. Intermediate recruitment groups reached peak performance in their mid‐reproductive life span and with intermediate breeding experience, before decreasing. Breeding success was lowest for the initial breeding attempt regardless of AFR, but we observed subsequent variation relative to recruitment age. Gaining experience by delaying recruitment positively influenced reproductive performance early in the reproductive life span and was most evident for the youngest breeders. Oldest recruits had the highest initial and peak breeding success. Differences in AFR resulted in trade‐offs in reproductive life span or timing of senescence but not in the overall number of breeding attempts. Patterns differed as a function of colony size, and thus competition for resources. Early life improvement in performance at the larger colonies was primarily due to within‐individual factors and at the largest colony, AFR. Regardless of colony size late‐life performance was positively related to the age at last reproduction, indicating selective disappearance of lower performing individuals. These results highlight that different life‐history strategies were equally successful, indicating that individuals can overcome potential trade‐offs associated with early‐ and late‐life performance. These results have important implications for understanding the evolution of life‐history strategies responsible for driving population change.
- PAR ID:
- 10452148
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Animal Ecology
- Volume:
- 90
- Issue:
- 4
- ISSN:
- 0021-8790
- Page Range / eLocation ID:
- p. 931-942
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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