Mate choice and courtship signal differentiation promotes speciation in an Amazonian frog

Female mate choice influences the evolution of male courtship signals and may promote speciation when those sexually selected traits also have a function in species discrimination. Here, we assess interpopulation female mate choice by conducting phonotaxis experiments on a population of the Amazonian frog Engystomops petersi in Puyo, Ecuador. Our results show very strong behavioral isolation relative to 1 of 2 foreign populations. Puyo females strongly discriminate against La Selva in favor of Puyo or Yasuní signals. In contrast, Puyo females do not discriminate against signals from Yasuní, which are similar in frequency. Behavioral isolation was stronger than expected because Puyo females were unable to recognize La Selva courtship signals as belonging to conspecific males. Overall, female mate choices are consistent with male courtship signal differentiation among populations but inconsistent with geographic or genetic distances. Simulations under a null model of undirected evolution (Brownian motion) suggest directional selection on courtship signals at La Selva. Based on our results, we hypothesize that sexual selection and/or reinforcement is driving speciation between E. petersi populations.