Evolutionary ecology of aging in the garter snake Thamnohis elegans

Background/Question/Methods Populations of garter snakes (Thamnophis elegans) have been studied in the Northern Sierra Nevada mountain range (USA) since 1976. Through intensive mark/recapture experiments and habitat monitoring, we have reported two ecotypes of garter snake. The fast growth ecotype occurs in low elevation sites in and around a dominant water source; they mature early  (2 – 3 years of age), reproduce often (annual litters averaging 7 offspring), and live short lives (median = 4 years of age) in the wild. The slow growth ecotype matures late (5 – 7 years of age), reproduces infrequently and with small litters (average = 3 offspring every 2 or 3 years), and lives longer (median = 8 years); slow growth animals are found in higher elevation mountain meadow sites. Laboratory reciprocal transplant experiments indicate that the fast and slow growth trajectories are due to genetic differences between the two ecotypes.

Results/Conclusions Laboratory experiments to test the cellular stress hypothesis of aging reveal that fast growth / short-lived animals: consume more (mass-independent) oxygen over a profile of temperatures; produce greater amounts of mitochondrial ROS per unit time; convert ADP to ATP less efficiently; and lack the ability to repair ionizing damage to DNA to pre-damage (baseline) levels.  In all measures, slow growth / long-lived animals outperform the short-lived ecotype.  These results suggest that evolution along the physiological axis governing oxygen consumption, mitochondrial function, and DNA repair underlie the evolution of lifespan, growth, and reproduction in these populations of garter snakes