Phylogeographic relationships among worldwide populations of the cosmopolitan marine species, the striped gray mullet (Mugil cephalus), investigated by partial cytochrome b gene sequences

Several factors such as geographical barriers, demographic history, biological and ecological traits may contribute to delineate the evolutionary history of a species. The gray mullet, Mugil cephalus, represents an interesting case of a marine species with a coastal ecology and a cosmopolitan distribution. In this study, partial cytochrome b sequences were resolved for 177 M. cephalus specimens sampled from 14 different geographic sites, in order to investigate the genetic divergence and the phylogeographic relationship among populations at a global scale. Demographic parameters were also assessed. Analysis of partial cyt b sequences showed high levels of differentiation among populations from distant geographic areas as most populations harbored private alleles and showed reciprocal monophyly. Both phylogenetic trees and haplotype network indicate the East Australian haplotypes as the closest to the ancestor sequences, which leads to the hypothesis of an Indo-West Pacific center of origin for M. cephalus. The analyses of the molecular variance showed that the genetic variation in M. cephalus is mainly harbored among populations rather than within populations. The high variability indices (h, π) calculated on M. cephalus individuals pooled together and the very low variability indices detected at some geographic sampling sites suggest that gray mullet populations have undergone a long-term reproductive isolation characterized by events of population abundance reductions which may have favored genetic differentiation among populations.