Late Pleistocene dispersal of Indian-Pacific sardine populations in an ancient lineage of the genusSardinops

Temperate sardines fall into two related monotypic genera,Sardina andSardinops. Sardina exists as a cluster of subpopulations in the northeastern Atlantic and Mediterranean, andSardinops encompasses five geographically-isolated regional populations: (1) South Africa-Namibia, (2) Australia-New Zealand, (3) Chile-Peru, (4) Mexico-California and (5) Japan-Russia. We surveyed electrophoretic variability in the products of 34 protein encoding loci inSardina (N=26) and the five Indian-Pacific populations ofSardinops (N=222), collected from 1983 to 1991. Nei's genetic distances (molecular clock calibrated by the rise of the Panama Isthmus and the opening of the Bering Strait, these genetic distances correspond to times since divergence of <200 000 yr. AlthoughSardinops populations showed a significant degree of allele-frequency heterogeneity (FST, a measure of population differentiation, averaged 0.085 over 8 polymorphic loci), the distribution of genetic distances and tests of allele-frequency heterogeneity could not distinguished between hypotheses of north-south antitropical or east-west oceanic dispersal. Low levels of gene diversity inSardinops and mutation-drift disequilibria are consistent with a strong reduction in population size before the Late Pleistocene dispersal to the corners of the Indian-Pacific Oceans of an ancestralSardinops population.