Biodiversity of the Buffalo Leeches Genus (Arhynchobdellida, Hirudinidae) in Southern Thailand Revealed from DNA Barcoding.

Leeches in the genus Whitman, 1886, also known as buffalo leeches, are blood-sucking ectoparasites of vertebrates. Although they are widely distributed in Asia and had been highly abundant in the past, studies on diversity and taxonomy of this genus are still scarce. There is probably a large amount of cryptic diversity yet to be discovered, particularly from mainland Southeast Asia. In this study, we used morphology and DNA barcoding with a gene fragment to explored the diversity of leeches in the southern region of Thailand, where a unique geographic feature could have led to the diversification of freshwater biota. Molecular phylogenetic analyses and species delimitation approaches (ABGD, bPTP, GMYC, and BOLD) revealed the presence of four putative species of leeches from southern Thailand, including , , and two morphologically cryptic lineages of . Compared to other leech genera, genetic distances of leeches were relatively low (0.11-0.65% within species; 3.72-14.36% between species) and barcoding gaps were very narrow (1.54-2.88%). The species diversity, distribution pattern, and a phenomenon of low genetic divergence of leeches in southern Thailand could be explained by an ancient seaway, paleo-drainage, and anthropogenic activities.