Genetic and reproductive evidence of natural hybridization between the sister species rhinella atacamensis and rhinella arunco (Anura, Bufonidae)

Abstract

Rhinella atacamensis and Rhinella arunco are sister species which, together, are distributed from 25°S to 38°S in Chile. Until recently they were considered to be allopatric, with the dividing line around 32°S, but in 2007 a possible zone of secondary contact was found in the Estero Pupío (32°S). We investigated the species status of adult individuals of three localities along this creek using AFLP markers. Data were analyzed with a Bayesian method that allowed the identification of different types of hybrids in a population. In two of the localities in the lower part of the watershed, the majority of the individuals were identified as backcrosses of hybrids with R. arunco or first generation hybrids, although a few individuals were classified as pure R. arunco. This information, supplemented by mitochondrial sequences and reproductive observations in both the laboratory and in the field, shows that hybridization has been a recurrent phenomenon at these two localities. By contrast, in