Micro‐geographic shift between negligible and actuarial senescence in a wild snake

Abstract

1. While it has long been known that species have contrasted life expectancy (pace of mortality) and generation time (pace of reproduction), recent studies have also uncovered that the shape of adult age trajectories of mortality and reproduction can vary remarkably among species along a continuum of senescence ranging from strong deterioration (senescence), insignificant deterioration (negligible senescence) to improvement with advancing age (negative senescence). 2. As for many long-lived ectotherms with asymptotic growth and increasing reproductive output with age, snakes are good candidates for negligible senescence to occur. Yet, intraspecific variation in the pace and shape of actuarial and reproductive senescence across wild populations of these species remains to be explored. 3. Here, we used 37 years of mark-recapture data in two nearby habitats inside a meadow viper Vipera ursinii population to quantify life expectancies, generation times and the shape of actuarial and reproductive senescence. 4. Female vipers maintained stable reproductive performances at old ages, even when accounting for the predicted increase of fertility with body size, providing evidence for negligible reproductive senescence in both habitats. 5. Males had a higher adult mortality and a shorter life expectancy on average than females and actuarial senescence shifted from negligible senescence in the optimal habitat to strong senescence in the sub-optimal habitat. 6. Overall, these results demonstrate that micro-geographic environmental variation can generate qualitative shifts in actuarial senescence patterns. This highlights that taking into account the within-species plasticity of age-dependent trajectories could prove useful in better understanding what determines the evolution of life-history age trajectories.

Slow and negligible senescence among testudines challenges evolutionary theories of senescence

“…In this work, we have studied populations under protected environments, and thus our results may not be reflective of aging rates and longevities in their natural environments. For instance, studies on vipers and frogs have found that populations can greatly vary their aging rates when exposed to different environmental conditions ( 14 , 15 ). We compared our results with data from natural environments for three species [ Chrysemys picta ( 13 ), Trachemys scripta ( 31 ), and Kinixys homeana ( 32 )].…”

“…These indeterminately growing species may gain survival advantages and larger reproductive potential with age, which allows them to invest more in somatic maintenance and potentially slowing senescence. To date, only a handful of studies have investigated senescence in animal species with indeterminate growth, such as turtles and tortoises (10)(11)(12)(13), where different populations of the same species can show evidence of both senescence and negligible senescence (12)(13)(14)(15). Thus, the question remains: Can some species slow or even avoid growing old?…”

Life span, growth, senescence and island syndrome: Accounting for imperfect detection and continuous growth

“…Compared with mammals and birds (Owen et al, 2008 ), ageing in reptiles is much slower (e.g. Tully et al, 2020 ; Warner et al, 2016 ). Warner et al ( 2016 ) suggested that this is because the fitness benefits at large sizes may overcome the ‘declining power of natural selection with advancing age’.…”

The Natural History of the Northern Black Racer (Coluber Constrictor Constrictor) in South-Central Pennsylvania

“…It is possible that unreliable and anomalous wintering conditions, possibly derived from climate change, are harming the physiological conditions of this species. Long-term studies in southern France demonstrated that micro-geographic environmental variation can generate qualitative shifts in actuarial senescence patterns in the Meadow Viper, Vipera ursinii, (Tully et al 2020). This suggests that the colder temperatures during the winters between the sampling periods, which were abnormally cold and fell below the long-term winter average temperatures, may have caused widespread mortality among Northern Black Racers.…”