Hormuz River System as a micro hotspot of diversification for the aphaniid fishes in Iran

The Hormuz River System (HRS) is located in the southern coastal plain of the Zagros Mountains. Two main river drainages i.e., Mehran and Kol are known from this region, which are directly discharged to the Persian Gulf. The HRS has surprising diversity for tooth-carp fishes (family Aphaniidae). The present study aims to accentuate this notable diversity and discuss the possible cause of diversification of the tooth-carps in the HRS. To date, 15 Aphaniid species have been discovered from the Iranian drainage basins. Among them, 10 species belong to the genus Aphanius, four species belong to the genus Aphaniops, and a single species belonging to the genus Paraphanius. The HRS by having four species (22% of the Iranian tooth-carps) demonstrated the highest diversity among the other Iranian basins. Of these, one belongs to the genus Aphanius (A. darabensis) and three species belong to the genus Aphaniops (A. furcatus, A. ginaonis, and A. hormuzensis). By considering the degree of endemicity of the tooth-carps fauna relative to the territorial boundaries of drainages, the HRS has the highest endemicity, in which 31% of the Iranian endemic toothcarp species present only in the HRS. The last connection of the Makran Basin with the HRS dates back to the late Pliocene and lower Pleistocene about 1.8 million years ago. Also, the other vicariance-based events like those events related to the last glacial maximum (21000- 18000 BP), population migration during the Early Holocene sea-level rise, and the Holocene to present-day have promoted the intra- and interspecific differentiation of tooth-carps in the HRS. Also, the geological situation of the HRS provided various extreme environmental conditions, which caused a particular increase in the diversification of the tooth-carp species.