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.
The field of comparative ageing biology has greatly expanded in the past 20 years. Longitudinal studies of populations of reptiles with a range of maximum lifespans have accumulated and been analysed for evidence of mortality senescence and reproductive decline. While not as well represented in studies of amniote senescence, reptiles have been the subjects of many recent demographic and mechanistic studies of the biology of ageing. We review recent literature on reptile demographic senescence, mechanisms of senescence, and identify unanswered questions. Given the ecophysiological and demographic diversity of reptiles, what is the expected range of reptile senescence rates? Are known mechanisms of ageing in reptiles consistent with canonical hallmarks of ageing in model systems? What are the knowledge gaps in our understanding of reptile ageing? We find ample evidence of increasing mortality with advancing age in many reptiles. Testudines stand out as slower ageing than other orders, but data on crocodilians and tuatara are sparse. Sex‐specific analyses are generally not available. Studies of female reproduction suggest that reptiles are less likely to have reproductive decline with advancing age than mammals. Reptiles share many physiological and molecular pathways of ageing with mammals, birds and laboratory model organisms. Adaptations related to stress physiology coupled with reptilian ectothermy suggest novel comparisons and contrasts that can be made with canonical ageing phenotypes in mammals. These include stem cell and regeneration biology, homeostatic mechanisms, IIS/TOR signalling, and DNA repair. To overcome challenges to the study of reptile ageing, we recommend extending and expanding long‐term monitoring of reptile populations, developing reptile cell lines to aid cellular biology, conducting more comparative studies of reptile morphology and physiology sampled along relevant life‐history axes and sequencing more reptile genomes for comparative genomics. Given the diversity of reptile life histories and adaptations, achieving these directives will likely greatly benefit all ageing biology.
A free
- NSF-PAR ID:
- 10458552
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 34
- Issue:
- 1
- ISSN:
- 0269-8463
- Page Range / eLocation ID:
- p. 38-54
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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