Body size and agonistic experience affect dominance and mating success in male copperheads

Fighting behaviour in adult male copperheads, Agkistrodon contortrix (Serpentes, Viperidae), was investigated in the laboratory to assess the relative importance of body size and type of agonistic experience as determinants of dominance and mating success. Seven experiments were conducted. In each experiment, trials were run using two adult males and one female in a large arena. The first experiment tested the influence of body size. All males tested had no recent fighting experience for 6-12 months, and one male of each pair was 8-10% longer in snout-vent length and had greater mass. In all cases, larger males won fights and were first to locate, court and guard females; thus, larger snout-vent length was an important determinant of fighting success and priority of access to potential mates. Males with either winning or losing experience from the first experiment were used in six subsequent experiments on the relative importance of snout-vent length and agonistic experience in attaining dominance and mating success. Losing experience had a greater effect than snout-vent length on subsequent fighting success and gaining priority of access to females. Winning experience, in contrast, did not increase the probability of winning subsequent fights; however, winners appeared more excitable and none deferred from challenges of other males. The asymmetry in effects of single experiences of victory and defeat is consistent with studies on other vertebrates and supports the hypothesis that losing fights in males negatively affects behaviour directly related to their fitness.