Morphological-genetic analysis of Potamothrix hammoniensis (Michaelsen, 1901) (Clitellata: Oligochaeta) with phylogeographic inferences: a case study in Türkiye

Potamothrix hammoniensis (Michaelsen, 1901) is one of the freshwater Clitellata species of Ponto-Caspian origin. Nearly 30 distinct morphological taxonomic characters are used for identification at the species level within the phylum Annelida. It is predicted that this species will show patterns of speciation dependent on allopatric isolation in relation to distribution barriers in the phylogeographic history of the species. The geography of Türkiye has many barriers capable of isolating aquatic organisms regardless of whether their active distribution is limited or not. In this study, P. hammoniensis (Oligochaeta) samples were collected in eight natural lakes (Lakes Gala, Büyük Akgöl, Sapanca, Eğirdir, Mogan, Cernek, Gölbaşı, and Nemrut) located in different geographical regions from the west to east of Türkiye between 2010 and 2013. These lakes have geographically isolation barriers among them and are thought to best reflect allopatric isolation. The samples were described based on both morphological differentiation and molecular characterisation using the data of COI and ITS2 fragments. According to the obtained results, the species of interest is not represented by a single species in the distribution area of Türkiye. The samples determined from Lake Gala may represent a new species. The samples obtained from Lakes Sapanca and Eğirdir show differentiation, but this differentiation is not as high as that observed for the Lake Gala samples. The Lake Nemrut samples also had a high rate of differentiation with an isolation process and mechanism that differed from those of the samples of all other investigated lakes.