Taxonomic and phylogenetic relationships of freshwater crabs of the genus Potamon (Crustacea: Brachyura: Potamidae) from Iran

In an era of climate change and habitat destruction, assessing current biodiversity as soon as possible is of crucial importance. To uncover the real biodiversity, taxonomic problems in species complexes and phylogenetic delimitations of species need to be clarified. Potamon is a well-known freshwater crab genus with a distribution from the Middle East through southern Europe and the far north of Africa. Phylogeny of Potamon has been a source of disagreement among specialists over the last few decades. In order to understand the evolution of the group it is crucial to resolve the phylogenetic relationships among the species of Potamon and to discover intraspecific endemic units using different tools. The purposes of the current study were: 1) to reconstruct the phylogenetic history of different species of the genus Potamon in Iran, 2) to find out, if there is consistency of morphological with molecular characters, 3) to determine intraspecific molecular variability among populations of Potamon elbursi in order to understand initial steps of regional differentiation as well as importance of endemic forms for conservation issues. In the course of the study two mitochondrial (16S rRNA and Cox1) and one nuclear (28S rRNA) genes were partially amplified and sequenced. A significant divergence was shown among three distinct lineages previously considered to belong to Potamon persicum complex and associated with their geographical distributions. One lineage corresponds to a formerly synonymised species, P. elbursi, which is here revalidated and redescribed. Another lineage (western Iran) still must be considered a cryptic lineage, since it is genetically distinct, but the current morphological evidence cannot separate it from P. persicum. Consistent molecular and morphological divergence was also recorded from the westernmost slopes of the Zagros Mountains where Potamon ilam, a sister species to Potamon mesopotamicum, is described as a new species to science. Overall, our results show that Potamon radiated at different time intervals in the Middle East, leaving a genetic footprint of historical differentiation processes and following successive isolation within different watersheds. The current locally confined and unique biological diversity of Iran can be explained mainly by different topography and climate regimes resulting from mountains uplifting. Genetic assessment of populations of P. elbursi elucidates a significant genetic differentiation among populations without any linkage with geographical dispersal. Some populations show high endemicity, resulting from strong genetic drift or geographic barriers. Endangered aquatic ecosystems and occurrence of genetically distinct endemic and isolated populations of P. elbursi, call for considering the Alborz Mountains for possible future conservation plans