Do different populations of Aphanius dispar in Southern Iran form Operational Taxonomic Units (OUTs)?

Deciphering the exact fundamental relations of morphological differentiation among isolated populations of animal species is generally difficult. Usually changes in morphology are resulted from adaptation to different environmental conditions (ecoplasticity) or represent an expression of genetic differences and/or gene pool pauperization, and in most instances, however, changes in morphology are the result of the interplay between environmental factors and genetic plasticity. In this study, the morphology and molecular phylogenies of common tooth-carp populations (Aphanius dispar) were studied in three basins in Southern part of Iran to discuss an important aspect relate to the question whether morphologically differentiated populations of a single species function as Operational Taxonomic Units. All morphological analyses were revealed significant and strong morphological differentiation between the populations that corresponds well with their zoogeography and their molecular phylogeny in geographically isolated basins. Therefore, it can be concluded that when the interaction between gene flow among populations and natural selection is resulted owing to a long evolutionary history, then the observed morphological differences can be functioned as different Operational Taxonomic Units (OTUs) in subspecies or even species levels. In addition, biological characteristics of the A. dispar, its high tolerance, geological and ecological conditions in Southern Iran are the main factors that increase chance of reproductive isolation and genetic diversity in this region.