2004 Heritable variation in testosterone levels in male garter snakes (Thamnophis sirtalis

Circulating testosterone levels were measured at 195, 318 and 437 days of age in 76 male garter snakes (Thamnophis sirtalis) born to 26 wild-caught females. Testosterone levels increased significantly with increasing mass at all three ages and differed significantly among families at 318 and 437 days. ‘Full-sib ’ estimates of heritability were near one at 318 and 437 days but these estimates may be inflated by maternal effects, dominance and epistasis. Evidence of heritable variation in circulating testosterone levels suggests that the evolution of traits affected by this hormone (reproductive, territorial and agonistic behaviour; body size and shape) might be mediated through changes in this hormonal control mechanism