Species level hidden diversity within morphospecies: Anatolia-based evolution and cryptic species diversity in the Simulium (Wilhelmia) equinum species group (Diptera: Simuliidae)

Cryptic species are black boxes of taxonomy and need to be addressed with an integrative taxonomic approach. Simulium (Diptera: Simuliidae) may contain a substantial amount of cryptic species diversity due to its large cross-continental distribution and habitat-based canalization in taxonomic characters. Except for Simulium sergenti, the following six species Simulium equinum, Simulium paraequinum, Simulium pseudequinum, Simulium turgaicum, Simulium balcanicum, and Simulium lineatum are the most widely distributed species of the subgenus Wilhelmia in the Palearctic region. However, the conspecific diversity and evolutionary history of these species are not yet well understood. In this study, therefore, we used mitochondrial COI and nuclear ITS1-2 sequences to perform species delimitation tests, and demographic and phylogeographic analyses to understand candidate species and evolutionary history of the seven species. While our results did not support the species status of S. balcanicum, S. turgaicum, and S. lineatum, it did suggest several candidate species within S. equinum and S. pseudequinum. Molecular clock analysis revealed that significant branching events occurred in the Pliocene, and demographic fluctuations in the populations occurred intensely during the Pleistocene. Overall, the results indicated that Anatolia has served as a significant refugium for ancestral haplotypes, and it is an important dispersal corridor between the eastern and western Palearctic for Wilhelmia species.