Pattern of differentiation in the annual killifish genus Austrolebias (Cyprinodontiformes: Rivulidae) from a biosphere reserve site in South America: a multidisciplinary approach

Abstract

The annual killifish genus Austrolebias includes approximately 38 species distributed throughout the Parana-Plata basin and Patos-Merin system. Within the Austrolebias adloffi species complex, the Uruguayan populations of Austrolebias charrua were considered as an intergradation between A. adloffi and Austrolebias viarius populations. Austrolebias charrua presents an intermediate phenotype between both taxa and high levels of morphological and chromatic variability. In the present study, we incorporate different methodological approaches (molecular, morphology, and gamete ultrastructure) to elucidate the pattern of differentiation among the parapatric taxa (A. charrua, Austrolebias reicherti, A. viarius) distributed in a Biosphere Reserve Site. Analyses of cytochrome b sequences show high values of DNA polymorphism, in particular for A. charrua. This is in accordance with both morphological and gametic variation. Using a statistical parsimony network based on these sequences and analysis of morphological data, past fragmentation and range expansion involving perhaps secondary contact between A. charrua and A. reicherti could be proposed. Coloration pattern and morphometric analyses showed an unexpected higher similarity between the most distantly-related taxa, A. viarius and A. charrua. This could be the result of retention of ancestral polymorphisms, especially in A. charrua populations from ponds of higher elevation, or to directional selection acting in similar ecological environments. Because these annual killifish species are considered endangered, our work reinforces the high priority need to include them in a conservation programme. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 620–635.