The evolution of aging phenotypes in snakes: a review and synthesis with new data

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Abstract
Reptiles are underutilized vertebrate models in the study of the evolution and persistence of senescence. Their unique physiology, indeterminate growth, and increasing fecundity across the adult female lifespan motivate the study of how physiology at the mechanistic level, life history at the organismal level, and natural selection at the evolutionary timescale define lifespan in this diverse taxonomic group. Reviewed here are, first, comparative results of cellular metabolic studies conducted across a range of colubrid snake species with variable lifespan. New results on the efficiency of DNA repair in these species are synthesized with the cellular studies. Second, detailed studies of the ecology, life history, and cellular physiology are reviewed for one colubrid species with either short or long lifespan (Thamnophis elegans). New results on the rate of telomere shortening with age in this species are synthesized with previous research. The comparative and intraspecific studies both yield results that species with longer lifespans have underlying cellular physiologies support the free-radical/repair mechanistic hypothesis for aging. As well, both underscore the importance of mortality environment for the evolution of aging rate.