Cryptic genetic diversity and molecular detection of Trypanosoma theileri complex in the deer fly Chrysops dispar Fabricius from Thailand

The deer fly (Diptera, Tabanidae), Chrysops dispar Fabricius is a common and widespread pest and vector species transmitting pathogens to animals including economically significant livestock. However, there is only limited information on genetic diversity, which crucial for understanding disease epidemiology. In this study, we examined genetic diversity of C. dispar collected from northeastern Thailand and compared with Indian material, from where this species was originally described. A molecular approach was used to screen for trypanosome. High genetic diversity was found within Thai C. dispar specimens with maximum 3.10% intraspecific genetic divergence due to the existence of two cryptic genetic lineages. Because these lineages coexist geographically, this indicates some degree of isolation, or the early stage of speciation. Phylogenetic analyses between Thai and Indian C. dispar populations revealed that they are genetically clearly distinct with minimum genetic divergence of 2.59%. A molecular species delimitation analysis supported that they belong to different species. Molecular screening of trypanosomes revealed that 20 of 90 specimens were positive and 16 of these were successfully sequenced. Based on sequence similarity, all were belonging to Trypanosoma theileri complex detected in cattle, the first report of this parasite in C. dispar. Phylogenetic analyses revealed that they belonged to two lineages (TthI and TthII) of this protozoa, corresponding to the occurrence of this parasite found in cattle in Thailand.