Nuclear and mitochondrial data reveal high genetic divergence among Atlantic and Mediterranean populations of the Iberian killifish Aphanius iberus (Teleostei: Cyprinodontidae).

The molecular divergence and phylogenetic relationships of the Iberian populations of Aphanius iberus were established using allozymes and the complete cytochrome b gene sequence. Congruent results were found with both nuclear and mitochondrial molecular markers. The Mediterranean and Atlantic populations are clearly differentiated into two independent lineages. Their high molecular divergence suggests an early isolation, and the absence of gene flow among the populations indicates their independent evolution. The nuclear and mitochondrial data reveal monophyletic clustering of the two geographical lineages, but provide weak support for the population relationships. However, the mitochondrial results differentiated the Villena population as a distinct mitochondrial unit within the Mediterranean group. Geographically broad studies across the distribution range of A. iberus have helped to elucidate the patterns of diversification of this species. The genetic divergence found between the Atlantic and the Mediterranean populations is of the same order as those found among recognized species of cyprinodontids. The identification of two discrete evolutionary lineages has important implications for the conservation of this species, since its recovery requires the recognition and preservation of natural diversity. The Mediterranean and Atlantic lineages should be managed separately to avoid loss of their genetic identity, and the genetic uniqueness of the populations should be preserved by using wild stocks as the source of genetic diversity in captive breeding programmes.