Genetic divergence between three sea urchin species of the genus Strongylocentrotus from the Sea of Japan

Intraspecific allozymic variation and interspecific genetic divergence were studied in three sea urchin species of the genus Strongylocentrotus (S. in termedius, S. nudus, S. pallidus) from the Sea of Japan. S, pallidus and S, intermedius showed high mean values of expected heterozygosity, H-e = 0.22 3 +/- 0.072 (17 loci) and H-e = 0.230 +/- 0.065 (19 loci), respectively. Th is estimate was somewhat lower in S. nudus, H-e = 0.126 +/- 0.043 (17 loci) . Estimates of Nei's genetic distance between S, nudus/S. intermedius (D = 1.578, 17 loci) and S. nudus/S. pallidus (D = 1.327, 15 loci) were consider ably higher than that between S. intermedius/S. pallidus (D = 0.269, 17 loc i), Invoking the protein clock hypothesis and using Panamanian geminate sea urchins for protein clock calibration, the time of divergence between S. i ntermedius and S, pallidus was estimated as 2.7 MY. The results obtained fo r S. intermedius and S. nudus by us differ considerably from results obtain ed for these species by Norimasa Matsuoka and coworkers. The revealed discr epancies are discussed and the conclusion made that Matsuoka and coworkers' data on echinoderm biochemical genetics and systematics should be used wit h caution. (C) 2000 Elsevier Science Ltd. All rights reserved.