Seasonal changes in agonistic behaviour of the western red-backed salamander, Plethodon vehiculum

Abstract

The objectives of this study were (1) to describe the behaviour of adult western red-backed salamanders, P. vehiculum, in intrasexual encounters, and (2) to test specific hypotheses to elucidate the adaptive contexts in which agonistic behaviour occurs in this species. Two alternative hypotheses were tested. (1) Levels of aggression peak during the mating season in the autumn and are relatively low among individuals of both sexes at other times of the year (agonistic behaviour is associated with mating), or (2) levels of aggression are relatively high among individuals of both sexes throughout the year (agonistic behaviour is associated primarily with competition for resources other than mates). A further prediction, based on the theory of sexual selection, was that males are more aggressive than females during the peak mating season in the autumn. The behaviour of P. vehiculum was to a large extent similar to that reported for other species of plethodontids, but a few behaviours, tentatively designated as threat displays have not been previously described. Seasonal changes and sexual differences in the frequency of agonistic behaviour were in accordance with hypothesis (1) as stated above. Agonistic behaviour was largely confined to male-male encounters in the autumn and was infrequent in these encounters outside the mating season as well as among females at all times of the year. As predicted, in the autumn males were more aggressive than females. Agonistic behaviour of P. vehiculum is therefore primarily associated with mating behaviour.