A new and unique species of the genus Aphanius Nardo, 1827 (Teleostei: Cyprinodontidae) from Southern Iran: A case of regressive evolution

Abstract

A primarily vicariance-based speciation has been suggested for the killifish genus AphaniusNardo, 1827, but ecological factors are likely to have promoted the speciation processes in addition. Here, we report on the discovery of a unique Aphanius species from Southern Iran and show that also regressive evolution has shaped the present-day diversity of Aphanius. The species is characterized by complete absence of scales and reduction in the biomineralization of hard structures, particularly of the caudal skeleton and jaw teeth. Based on mt-DNA sequences, morphometric and meristic data, osteology, jaw teeth and otoliths, it is described as Aphanius furcatus sp. n. The new species is sympatric with A. dispar (Rüppell, 1829) in salty rivers and hot sulphuric springs in the Hormuzgan Basin (Southern Iran), and is sister taxon to this species plus A. ginaonisHolly, 1929. Based on geological data we estimate that the divergence between the lineages of A. furcatus and A. dispar is about 12–14million years old. We conclude that the reductive phenomena observed in A. furcatus have evolved as an evolutionary response to the extreme habitat conditions in order to save energy (because storage of Ca2+ is not necessary), and to transport oxygen efficiently. The results confirm that regressive evolution is an important factor in speciation and occurs independently in separate lineages.