Insights into the molecular diversity and phylogeographic structure of Tabanus bifarius Loew, 1858 (Diptera: Tabanidae)

Tabanus bifarius Loew, 1858 is a horsefly species distributed throughout the Mediterranean region and in the areas of central and southeastern Europe and partly in Asia. In this study, we conducted the first comprehensive phylogeographic and population genetic analysis of T. bifarius collected from 13 localities across Türkiye and Iran, through utilizing mitochondrial (COI) and nuclear DNA (ITS1–5.8S–ITS2) markers. A total of 81 haplotypes and 59 nuclear alleles were identified among 187 sequenced individuals. Both mitochondrial and nuclear DNA patterns and diversity observed in T. bifarius are indicative of complex historical and demographic processes. Among all the populations studied, Eskişehir and Hatay exhibited the highest genetic diversity, which may be due to the region’s topography and transitional zones. Phylogenetic analyses suggested that T. bifarius split from the outgroup species approximately 5.53 million years ago (MYA) during the Late Miocene–Early Pliocene, likely driven by tectonic and climatic events. Subsequent diversification events that occurred during times of climatic and environmental fluctuations in the Late Pliocene and Early Pleistocene also seemed to have significantly affected the species and gave rise to the formation of some important genetic lineages. Our analyses results indicate that T. bifarius exhibits a structured genetic landscape shaped by multiple refugial routes, geographic barriers, and Quaternary climatic oscillations. Further, our findings suggest that the species likely entered Anatolia through three distinct routes: (1) from the Levant region into southern Anatolia via Hatay; (2) from the Caucasus into northeastern Anatolia through Ardahan; and (3) from the Iranian Plateau into eastern Anatolia via Van.