Slow life-history strategies are associated with negligible actuarial senescence in western Palearctic salamanders

Abstract

Actuarial senescence (hereafter \"senescence\") has been viewed for a long time as an inevitable and uniform process. However, the work on senescence has mainly focused on endotherms (especially mammals) with deterministic growth and low regeneration capacity at adult stages, leading to a strong taxonomic bias in the study of aging. Recent studies have highlighted that senescence could indeed display highly variable trajectory shape that correlates with species life history traits. Slow life histories and indeterminate growth seem to be associated with weak and late senescence. Furthermore, a few studies have suggested that high regenerative abilities could make senescence negligible in several ectotherms (e.g., hydra and salamanders). However, demographic data for species that would allow testing of these hypotheses are scarce and fragmented. Here, we investigated senescence patterns in a group of salamanders (i.e. \"true salamanders\") from the Western Palearctic using capture-recapture data and Bayesian modeling. Our results showed that salamanders have slow life histories and that they experience negligible senescence. This pattern was consistent at both intra- and interspecific levels, suggesting that the absence of senescence may be a phylogenetically conserved trait. The regenerative capacities of true salamanders, and urodeles in general, likely explains why these small ectotherms have lifespans similar to that of large endotherms (e.g., ungulates, large birds) and undergo negligible senescence contrary to most amniotes including humans. Our study seriously challenges the idea that senescence is a ubiquitous phenomenon in the living world.