Phylogeography of the black fly Simulium aureohirtum (Diptera: Simuliidae) in Thailand

The black fly Simulium aureohirtum Brunetti (Diptera: Simuliidae) is geographically widespread and utilizes diverse habitats. Previous studies revealed high genetic diversity, suggesting that this species could be a species complex. In this study, we used mitochondrial cytochrome c oxidase II sequences to examine genetic structure and demographic history of S. aureohirtum in Thailand. High level of genetic variation was observed due to the existence of genetically divergent lineages (A, B, and C). Lineages A and C were geographically widespread, while lineage B was geographically restricted to the eastern part of Thailand. The geographic localization of lineage B suggested limitations in gene flow, which is most likely a result of ecologically different habitats. Large genetic differences between individuals of lineages A and C, but geographically sympatric distributions of the members of these lineages, are considered to represent an admixture of the populations that have evolved allopatrically. Historical environmental change during the Pleistocene glaciations is possibly the factor that drove the lineage divergence. Population demographic history analyses revealed recent population expansions in the three lineages dating back to the last glaciations. These observations further highlight the significance of the Pleistocene climatic change on current genetic structure and diversity of living organisms of the Southeast Asian mainland.