The Untapped Potential Of Reptile Biodiversity For Understanding How And Why Animals Age

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 Plain Language Summary can be found within the Supporting Information of this article.