Origin, radiation, dispersion and allopatric hybridization in the chub Leuciscus cephalus

Tho phylogenetic relationships of 492 chub (Leuriscus cephalus) belonging t o 89 Populations across the species' range were assessed using 600 base pai rs of cytochrome b. Furthermore, nine species belonging to the L. cephalus complex were also analysed (over the whole cytochrome b) in order to lest p otential allopatric hybridization with L. cephalus sensu stricto (i.e. the chub). Our results show that the chub includes four highly divergent lineag es descending from a quick radiation that took place three million years ag o. The geographical distribution of these lineages and results of the neste d clade analysis indicated that the chub may have originated from Mesopotam ia. Chub radiation probably occurred during an important vicariant event su ch as the isolation of numerous Turkish river systems, a consequence of the uplift of the Anatolian Plateau (formerly covered by a broad inland lake). Dispersion of these lineages arose from the changes in the European hydrog raphic network and, thus, the chub and endemic species of the L. cephalus c omplex met by secondary contacts. Our results show several patterns of intr ogression, fr om Leuciscus lepidus fully introgressed by chub mitochondrial DNA to Leuciscus borythenicus where no introgression at all was detected. We assume that these hybridization events might constitute an important evo lutionary process for the settlement of the chub in new environments in the Mediterranean area.