Patterns of population differentiation in annual killifishes from the Parana-Uruguay-La Plata Basin: the role of vicariance and dispersal

Aim To elucidate the role of vicariance versus dispersal at the microevolutionary scale in annual killifish populations belonging to the Austrolebias bellottii species complex (Rivulidae). Within this complex, A. bellottii and A. apaii have low vagility and occur widely within the study area, making them excellent models for testing biogeographic hypotheses of differentiation. Location South America, in the Parana-Uruguay-La Plata river basin. Methods Molecular data and morphometric analyses were used to reconstruct the phylogeographic history and morphological variation of 24 populations of two taxa of the A. bellottii species complex. Phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) model-based methods, estimates of clade divergence times implemented in beast, non-metric multidimensional scaling, analysis of molecular variance results, and morphological analyses elucidated the role of vicariance versus dispersal hypotheses in population differentiation in the aforementioned river basin. Results In the A. bellottii species complex from the Parana-Uruguay-La Plata river basin, past allopatric fragmentation from vicariance events seems to be the most plausible scenario for diversification since the Late Miocene and more recently since the Plio-Pleistocene. The Plio-Pleistocene vicariance produced the differentiation of three major clades in A. bellottii populations. One clade from the eastern Uruguay River drainage was separated from another in western Uruguay and the Parana-La Plata River drainages. A later vicariance event split populations to the south (lower Parana-La Plata Basin) and north (middle Parana) of the western Parana River drainage. However, our results do not exclude the possibility of dispersal events among A. bellottii populations from both the Uruguay and Parana river drainages, which could occur in these river basins during hypothesized connectivity cycles of the Late Pliocene and Pleistocene. Main conclusions Past allopatric fragmentation caused by different vicariance events seems to be the main driver of diversification in the A. bellottii species complex since the Plio-Pleistocene. However, the current molecular data suggest that populations from both drainages of the Parana-Uruguay rivers may have experienced cycles of connectivity during the Pleistocene, perhaps including multiple vicariance or dispersal events from populations located in the western lower Uruguay River drainage, which encompassed climatic and geological changes in the Parana-Uruguay-La Plata Basin.