Phylogeographic analyses and taxonomic inconsistencies of the Neotropical annual fish Austrolebias minuano, Austrolebias charrua and Austrolebias pongondo (Cyprinodontiformes: Rivulidae)

Abstract

A significant portion of the threatened ichthyofauna is composed by annual fish, whose gene flow is commonly affected by large water bodies. Austrolebias minuano is an endangered species that lives in temporary wetlands of the Patos-Mirim Lagoon System, in Brazil, inhabiting both margins of the Patos Lagoon. This species has previously been target of taxonomic split, leading to the description of A. pongondo, and there are doubts about its distinction in relation to A. charrua. The objective of this study is to understand the evolutionary patterns and processes associated with the geographic distribution of A. minuano, A. charrua and A. pongondo, while assessing their taxonomic status. For this, specimens were collected along the distribution range of the three species, and sequences of the mitochondrial cyt b and CO1 and of the nuclear ENC1 gene were characterized. Phylogenetic and phylogeographic approaches showed subdivision of the dataset in four lineages: one clustering the type population of A. minuano with A. charrua, two presenting populations previously assigned to A. minuano that inhabit the Eastern margin of the Patos Lagoon and one corresponding to A. pongondo. Patterns of migration and genetic divergences support the assignment of each of these lineages as independent evolutionary units. In the chronophylogenetic reconstructions, the two lineages inhabiting the Western margin of the Patos Lagoon constituted the first to branch out whereas the eastern lineages diverged more recently. These divergences seem to have occurred before the Pleistocene Lagoon-Barrier Depositional System related to the paleogeographic evolution of the South American Coastal Plain.