Abstract
A general prediction of the neutral theory of evolution is that genetic diversity should correlate positively with effective population size. We show here that diversity across eight microsatellite loci was consistently and substantially lower in one common amphibian (Bufo bufo) than in another with similar life history traits (Rana temporaria) despite B. bufo having the larger breeding assemblage sizes. However, B. bufo breeding assemblages were much more highly differentiated than those of R. temporaria according to both Fst and Rst estimators. These differences occurred in shared habitats across identical geographical distances. The patterns of genetic diversity and differentiation detected in these two species were probably a consequence of high gene flow in R. temporaria but much lower gene flow among the larger but more dispersed B. bufo assemblages. These observations highlight the difficulty of defining the boundaries of wild populations, and show how two broadly similar species can exhibit very different population dynamics.