Sympatry and possible hybridization among species of the killifish genus Aphanius Nardo, 1827 (Teleostei: Cyprinodontidae) in Southwestern Iran

Studies of the taxonomy and present-day distribution of landlocked populations of the killifish Aphanius Nardo, 1827 (Cyprinodontidae) provide a key to understanding their zoogeographic history, and shape conservation strategies and habitat management. Here we report for the first time on the sympatric occurrence of the rare Mesopotamian tooth-carp A. mesopotamicus with a member of the widely distributed common tooth-carp (A. dispar group). Both were found in the Shadegan Wetland of the Mesopotamian drainage system (Southwestern Iran). External characters of individuals, otolith morphology and molecular data based on the cytochrome b gene confirm species identification. The otolith morphology of A. mesopotamicus, hitherto unknown, is strikingly similar to previously described otoliths of A. cf. pluristriatus from the Khonj stream (Southern Iran), which apparently reflects a close relationship between these recently diverged species. Several of the specimens recovered from the Shadegan Wetland showed intermediate characters in pigmentation, otolith morphology and some morphometric values. These specimens are interpreted as putative hybrids, which is additionally supported by a multivariate analysis of the morphometric data. Previous reports suggest that natural hybridization between species of Aphanius results largely from range overlap and range extension. A virtual distribution map derived from climatic modelling studies based on DIVA-GIS (7.5.0) indicates that sympatry of the A. dispar group and A. mesopotamicus is primarily determined by levels of precipitation during the warmest quarter, and is likely to occur only in Southwestern Iran.