Sexual dimorphism, and the spatial and reproductive ecology of the copperhead snake, Agkistrodon contortrix

Date of Completion

January 2007


Biology, Zoology




The spatial and reproductive ecology of the copperhead snake, Agkistrodon contortrix, was studied between 2001 and 2003 within the central Connecticut River Valley. Radio telemetered males (N = 11) and females (N = 7) showed significant annual and seasonal sex differences in home range size and movement levels. Male A. contortrix maintained larger annual home ranges and showed greater annual movement than females. Males also showed significantly larger home ranges and greater movement levels during the breeding season (August and September) than males during the non-breeding season, and females during both the breeding and non-breeding season. Timing of maximum male home range size corresponded to the single period of sexual activity and male home range size was positively correlated with number of reproductive partners. Both sexes showed fidelity to home range location and size, hibernation sites, and movement levels across years. ^ Males located females over long distances during the breeding season, presumably by following female chemical trails using their vomeronasal chemosensory systems (VNS), of which the forked tongue is the most obvious structure. Based on empirical studies, it has been proposed that the degree of tongue forking is directly correlated with trailing ability. Consequently, the tongue is a likely target of sexual selection. Eighty-four formalin-preserved museum specimens (41 males: 41 females) of adult A. contortrix were examined for evidence of sexual dimorphism of the tongue. Resulting data on tongue dimensions in adult males and females showed significant differences indicative of sexual dimorphism, and represent the first instance of tongue dimorphism in any tetrapod vertebrate. ^ Seasonal plasma T and P4 profiles of male A. contortrix showed a single late-summer peak that corresponds to the single breeding season. Although T and P4 have similar seasonal profiles, absolute levels of these steroids were notably different. Seasonal changes in T and P4 levels also corresponded to meiotic testicular activity. Testicular samples collected around the peak of sexual activity in September showed evidence of maximum spermiogenesis, while those collected in April and May showed complete meiotic regression. Examination of SSK tissue revealed hypertrophy of these structures in both non-breeding and breeding seasons. ^