SRegressive evolution of the cyprinodontid fishes

All known species of the cyprinodontid fishes are thriving in both inland and brackishwater environments. Some of them inhabited unusual habitats such as hot sulphuricsprings. Killifish genus Aphanius Nardo, 1827 is the only cyprinodontids in theMediterranean basins, Arabian peninsula and the Persian Gulf region. In theseregions, some Aphanius species show reduction in several external and anatomicalcharacteristics. To study, the evolutionary history of this reductive phenomenon inAphanius species, we applied both molecular and morphological evidences (two mt-DNA genes, osteology, jaw teeth and otoliths). The results showed that within thegenus Aphanius, reductive characters present for several species that clearly belongto separate lineages. Examples are Aphanius anatoliae and A. asquamatus fromAnatolia (reduced or lacking scalation); the extant Aphanius apodus and the fossilAphanius illunensis (absence of pelvic fins); A. illunensis shows also reduction in jawteeth cusps. Their habitats are characterized by a high concentration of NaR2RCOR3R,SOR4RP2-Por MgClR2R in water. A unique and new described species, Aphanius furcatusfrom Iran is also characterized by complete absence of scales and reduction in thebiomineralization of hard structures, particularly of the caudal skeleton and jaw teeth.This species also inhabits in extreme habitats, characterized by low oxygen, highwater temperatures, and high salt concentration. We concluded that the reductivephenomena observed in the mentioned cyprinodontid species have been evolved asan evolutionary response to the adaptation to adverse conditions and extreme habitatsin order to compete with the other taxa, and have been linked to adaptations andspeciation processes. Notably, these phenomena appear in different lineages ofcyprinodontid fishes.

کلیدواژه ها:

speciation ، Aphanius ، evolution ، extreme ecological conditions