Life-history strategies vary dramatically between the sexes, which may drive divergence in sex-specific senescence and mortality rates. Telomeres are tandem nucleotide repeats that protect the ends of chromosomes from erosion during cell division. Telomeres have been implicated in senescence and mortality because they tend to shorten with stress, growth and age. We investigated age-specific telomere length in female and male red-sided garter snakes, We hypothesized that age-specific telomere length would differ between males and females given their divergent reproductive strategies. Male garter snakes emerge from hibernation with high levels of corticosterone, which facilitates energy mobilization to fuel mate-searching, courtship and mating behaviours during a two to four week aphagous breeding period at the den site. Conversely, females remain at the dens for only about 4 days and seem to invest more energy in growth and cellular maintenance, as they usually reproduce biennially. As male investment in reproduction involves a yearly bout of physiologically stressful activities, while females prioritize self-maintenance, we predicted male snakes would experience more age-specific telomere loss than females. We investigated this prediction using skeletochronology to determine the ages of individuals and qPCR to determine telomere length in a cross-sectional study. For both sexes, telomere length was positively related to body condition. Telomere length decreased with age in male garter snakes, but remained stable in female snakes. There was no correlation between telomere length and growth in either sex, suggesting that our results are a consequence of divergent selection on life histories of males and females. Different selection on the sexes may be the physiological consequence of the sexual dimorphism and mating system dynamics displayed by this species.

Red-sided garter snakes (Thamnophis sirtalis parietalis) court and mate in early spring around large communal overwintering dens in central Manitoba. Emerging females are immediately covered by dozens or hundreds of vigorously-courting males, potentially imposing significant costs to the female. By manipulating numbers of courting males (both directly and by applying anticourtship pheromones), we quantified the degree to which female dispersal from the den is hindered by courtship. Courted females dispersed only about half as fast as did solitary females. Blood lactate levels were higher in mating than in courting or noncourting snakes of both sexes; the high levels of lactate in mating females support the idea that courtship is physiologically stressful to these animals, perhaps via constraints to female respiration. In arena trials, females that were exercised to exhaustion before courtship mated with smaller males than did control females. The spatial distribution of snakes around the den exhibits substantial heterogeneity, with densities often varying markedly between adjacent areas. Arena trials mimicking this heterogeneity showed that unmated females avoided parts of the enclosure containing scent cues from males. Our data support the hypothesis that courtship in T. s. parietalis confers significant costs to females, and that female behaviors have evolved to reduce those costs.

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