The Evolution of Courtship Behavior in Plethodontid Salamanders, Contrasting Patterns of Stasis and Diversification

An examination of courtship in salamanders helps resolve the puzzling problem of long-term evolutionary stasis in behavior. To address the companion issues of stasis and diversification, we summarize and synthesize courtship observations in Rhyacotriton and 13 genera of plethodontids. We use a modular analysis of courtship to identify conservative, as well as variable behavioral elements and sequences. We use time-calibrated, molecular phylogenies to reconstruct the evolutionary history of key elements in courtship at different time levels. In deep time (40–175 mya), we reconstruct the evolution of courtship among plethodontid genera, using Rhyacotriton and Ambystoma as outgroups. On a shorter time scale (10–40 mya), we reconstruct courtship history among species within three genera (Aneides, Plethodon, and Desmognathus). These reconstructions reveal extraordinary stasis for greater than 130 million years (Myr) in the courtship modules that align sexual partners and accomplish sperm transfer. Although some aspects of courtship pheromone delivery predate the origin of plethodontids in the early Cretaceous (66 mya), other aspects of delivery and preliminary courtship have diversified in the last 20–30 Myr. We argue that intricate aspects of sexual communication generate multivariate stabilizing selection that is responsible for evolutionary stasis lasting 100 Myr or longer.