LATE PLEISTOCENE DISPERSAL OF INDIAN-PACIFIC SARDINE POPULATIONS IN AN ANCIENT LINEAGE OF THE GENUS SARDINOPS

Temperate sardines fall into two related monotypic genera, Sardina and Sardinops. Sardina exists as a cluster of subpopulations in the north eastern Atlantic and Mediterranean, and Sardinops encompasses five geo graphically-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 product s of 34 protein encoding loci in Sardina (N = 26) and the five Indian- Pacific populations of Sardinops (N = 222), collected from 1983 to 199 1. Nei's unbiased genetic distances ((D) over cap) between samples of Sardina and Sardinops averaged 1.04 and are typical of distances betwe en species of related genera. (D) over cap s between the regional form s of Sardinops were less than or equal to 0.011, indicating that Sardi nops consists Of a single species with widely-scattered subpopulations . Assuming a molecular clock calibrated by the rise of the Panama Isth mus and the opening of the Bering Strait, these genetic distances corr espond to times since divergence of < 200 000 yr. Although Sardinops p opulations showed a significant degree of allele-frequency heterogenei ty (F-ST, 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 hypo theses of north-south antitropical or east-west oceanic dispersal. Low levels of gene diversity in Sardinops and mutation-drift disequilibri a are consistent with a strong reduction in population size before the Late Pleistocene dispersal to the corners of the Indian-Pacific Ocean s of an ancestral Sardinops population.