Nested cladistic analysis of Brazilian populations of Drosophila serido.

The effects of Quaternary climatic cycles were investigated in Drosophila serido, a Brazilian cactophilic fly widely distributed outside the Amazonian region. Previous studies have indicated this species displays remarkable karyotypic, male genitalia, and mtDNA variation, so much so that it has been described as a species complex, or superspecies. In the present study we expand the analysis of the mtDNA COI gene on D. serido populations, particularly in central Brazil, by obtaining DNA sequences from 248 individuals distributed across 47 localities. This allowed us to perform a nested clade analysis to discriminate historical from recurrent forces shaping the evolution of D. serido populations. The nested analysis indicates one event of past fragmentation separating populations from south and central Brazil (referred to as type B) from populations in central and northeast Brazil (type D) and 15 other significant events. The most common outcome of our analysis was contiguous range expansion and we discuss why this was expected in D. serido. Our data indicate that D. serido has been distributed across Brazil at least since the Mid-Pleistocene, which contradicts the hypothesis of current distribution being determined by last glaciation cycle. Nonetheless, we present evidence that climatic cycles during the Quaternary and before have had a significant impact on the differentiation of D. serido in Brazil. Our study confirms the usefulness of the nested clade analysis for disentangling the effects of historical and present-day forces shaping the evolution and distribution of a taxon.