tStudies of the taxonomy and present-day distribution of landlocked populations of the killifish AphaniusNardo, 1827 (Cyprinodontidae) provide a key to understanding their zoogeographic history, and shapeconservation strategies and habitat management. Here we report for the first time on the sympatric occur-rence of the rare Mesopotamian tooth-carp A. mesopotamicus with a member of the widely distributedcommon tooth-carp (A. dispar group). Both were found in the Shadegan Wetland of the Mesopotamiandrainage system (Southwestern Iran). External characters of individuals, otolith morphology and molec-ular 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. pluris-triatus from the Khonj stream (Southern Iran), which apparently reflects a close relationship betweenthese recently diverged species. Several of the specimens recovered from the Shadegan Wetland showedintermediate characters in pigmentation, otolith morphology and some morphometric values. Thesespecimens are interpreted as putative hybrids, which is additionally supported by a multivariate anal-ysis of the morphometric data. Previous reports suggest that natural hybridization between species ofAphanius results largely from range overlap and range extension. A virtual distribution map derived fromclimatic modelling studies based on DIVA-GIS (7.5.0) indicates that sympatry of the A. dispar group andA. mesopotamicus is primarily determined by levels of precipitation during the warmest quarter, and islikely to occur only in Southwestern Iran.
