Burst speciation processes and genomic expansion in the neotropical annual killifish genus Austrolebias (Cyprinodontiformes, Rivulidae).

The extent to which genome sizes and other nucleotypic factors influence the phyletic diversification of lineages has long been discussed but remains largely unresolved. In the present work, we present evidence that the genomes of at least 16 species of the neotropical rivulid killifish genus Austrolebias are unusually large, with an average DNA content of about 5.95 ± 0.45 picograms per diploid cell (mean C-value of about 2.98 pg). They are thus larger than the genomes of very nearly all other diploid, i.e. non-(paleo) polyploid species of actinopterygian fishes so far reported. Austrolebias species appear to be conventional diploids in all other respects and there is no reason to believe that they arise from polyploid ancestors. The genome sizes reported for other rivulid killifishes, including a putative sister group, are considerably smaller and fall within the range typical of most other cyprinodontoid species. Therefore, it appears that the ancestor(s) of contemporary Austrolebias have undergone one or more episodes of genome expansion encompassing sudden speciation process during the Pleistocene. In addition, these findings are consistent with the hypothesis of a positive correlation between species richness and genome size.