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

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.

State-dependent physiological maintenance in a long-lived ectotherm, the painted turtle (Chrysemys picta)

“…We predicted modest to no decline in immune function or DNA repair with increasing turtle size, as little senescence was anticipated (Bronikowski, 2008;Ungvari et al, 2008). We also predicted that immune function would be lowest in hatchlings because of immaturity of the immune system Sparkman and Palacios, 2009).…”

“…Ectothermic vertebrates have traits that suggest physiological maintenance patterns should deviate from those seen in previously studied endothermic vertebrates. For example, many reptiles are extremely long-lived and have increased reproductive output with age in adult females (as a result of indeterminate growth), suggesting that senescence should be minimal in these taxa and reduced in females compared with males (Patnaik, 1994;Congdon et al, 2003;Madsen et al, 2007;Bronikowski, 2008) (but see Congdon et al, 2001). Senescence in reproductive output appears to be nonexistent in long-lived reptiles (Congdon et al, 2001;Congdon et al, 2003;Sparkman et al, 2007).…”

“…Senescence in reproductive output appears to be nonexistent in long-lived reptiles (Congdon et al, 2001;Congdon et al, 2003;Sparkman et al, 2007). However, age-dependent physiological maintenance in long-lived taxa or in reptiles is largely unknown (Patnaik, 1994;Madsen et al, 2007;Robert et al, 2007;Bronikowski, 2008;Sparkman and Palacios, 2009). In addition, ectotherms experience torpor in temperate winters and aestivate in hot summers, which leads to reduced metabolism and movement, suggesting that maintenance should be lower either over the winter or summer, respectively, compared with other seasons.…”

Shorter telomere length with age in the loggerhead turtle: a new hope for live sea turtle age estimation

“…Although telomere length loss with age has been shown in several other taxa such as birds and humans ( Monaghan and Haussmann, 2006), this is the first publication that evaluated the trend in chelonians. In reptiles, age-related decrease in telomere length has been reported only in the American alligator (Alligator mississippiensis: Scott et al, 2006) and the garter snake (Thamnophis elegans: Bronikowski, 2008), but given the similarities in animal groups, we feel this method has potential in chelonians. For other taxa, telomere dynamics have generally not been investigated in epidermis samples, but in blood samples (Monaghan and Haussmann, 2006), with some exceptions in humans (e.g.…”

“…The reason why we could not find significant correlations both between age and telomere length and between telomere lengths in different tissues within individuals may be due to a limited sample size (n = 20). Otherwise, the lack of significant correlations may be methodological, i.e., other telomeremeasurement methods such as hybridization-based techniques might find strong patterns in chelonians like in other reptiles (Scott et al, 2006;Bronikowski, 2008;Haussmann and Mauck, 2008). In any case, telomere length in epidermis may be a useful estimator of not absolute but relative ages for sea turtles.…”