Genetic evidence of the presence of two species of Crassostrea (Bivalvia :Ostreidae) on the coast of Brazil

Although oysters are commercially very important in Brazil, there is still much dispute about the number of Crassostrea species occurring on the Brazi lian coast. The dispute is centered around C. brasiliana, considered by som e authors to be a junior synonym of C. rhizophorae. In this paper we compar ed, by allozyme electrophoresis, sympatric and allopatric populations of th e two putative species. Of the 17 loci analysed, five were diagnostic for t he two species in sympatry (gene identity = 0.46 to 0.37), clearly demonstr ating that they are distinct biological species. Heterozygosity (h) levels were high for both species (h = 0.24 to 0.28), and no heterozygote deficien cies were observed in any population (local inbreeding, F-IS = 0.141; P > 0 .70). Levels of population structure in C, rhizophorae along 1300 km of coa st were very low (population inbreeding, F-ST = 0.026; P > 0.15), indicatin g that the planktonic, planktotrophic larvae of these species are capable o f long-range dispersal.