Entrapped by the uneven central and Middle Eastern terrains: Genetic status of populations of Hirudo orientalis (Annelida, Clitellata, Hirudinida) with a phylogenetic review of the genus Hirudo.

Phylogenetic relationships between species of the genus Hirudo plus genetic variation in the entire distribution range of Hirudo orientalis were investigated based on mitochondrial (COI and 12S rDNA) and nuclear (ITS1+5.8S+ITS2) genome regions. The sister relationship of Hirudo orientalis and H. medicinalis was revealed with a high posterior probability. A broad and patchy distribution with minor genetic differences was observed in populations of H. orientalis along the central and Middle Eastern parts of Asia. The known distribution range occurred in topographically heterogeneous landscapes around the Caspian Sea. The demographic analysis suggests the selection of the COI locus under unfavourable respiratory conditions, but population size expansion cannot be fully rejected. The genetic variation trend indicated northward dispersal. Higher haplotype diversity in the South Caspian region potentially suggests the area as a historical refugium for the species. The vast dispersal is assumed to occur after the Pleistocene glaciations via vertebrate hosts.