Geographical variation in agonistic behaviour in a ring species of salamander,Ensatina eschscholtzii

Abstract

Ensatina eschscholtziiis a plethodontid salamander with several geographical races distributed in a ring-like series throughout the coastal mountains and inland Sierra Nevada mountains of California. Populations of these salamanders show genetic and morphological divergence, and in this study, we examined divergence in overt aggressive, passive aggressive/exploratory, avoidance and sensory behaviours in four populations. Two of the populations represent a zone of secondary contact between coastal and inland lineages ofEnsatina. We recorded behaviour of resident salamanders paired with same-sex intruders during the non-courtship season. The residents’ behaviour was affected independently by the population of the resident and the population of the intruder but not by the interaction between the resident population and the intruder population. Levels of agonistic and sensory behaviour showed a high degree of constraint among the populations. These behaviours also showed divergence among coastal and inland populations, and the geographical variation in behaviour is consistent with the phylogenetic history ofEnsatina. Convergent evolution of behaviour appears to have occurred at the zone of secondary contact between the coastal and inland lineages. Variation in agonistic and sensory behaviour among the populations observed and between the sexes suggests that there may be geographical and sexual variation in territoriality or competition.