Does the Mediterranean killifish Aphanius fasciatus (Teleostei: Cyprinodontidae) fit the one-dimensional stepping-stone model of gene flow?

Abstract

Five samples (30 individuals each) of the Mediterranean cyprinodontid fish, Aphanius fasciatus, were analysed by allozyme electrophoresis for a study concerning genetic structure and gene flow among populations. Forty-three loci, twelve of which were polymorphic at P0.99 level, were analysed. A. fasciatus showed low levels of genetic polymorphism, with expected heterozygosity values ranging from 0.027 (SE = 0.013) to 0.064 (SE = 0.023). The modified Rogers' genetic distances ranged from 0.053 to 0.202. The observed pattern of genetic differentiation among populations, obtained by multidimensional scaling of the modified Rogers' genetic distances, was consistent with geographic distribution. Coancestry coefficient (θ = 0.302, SE = 0.045) indicated a very high degree of genetic subdivision among populations and the estimate of gene flow (the effective number of migrants per generation, Nm = 0.445), computed by Wright's method, showed very restricted gene flow among populations. The regression analysis carried out using log-transformed values of geographic distance against M^ (pairwise values of Nm) gave a regression coefficient, b = −1.03, indicating that a restricted migration rate among populations can occur according to the one-dimensional stepping-stone model. The amount and modality of gene flow in A. fasciatus inferred from the results of the present study are consistent with the absence of dispersal stages and with the fragmented nature of brackish-water habitats along the coasts.