Population structure and genetic variability of pearl oyster Pinctada mazatlanica along Pacific coasts from Mexico to Panama

Populations of the Calafia pearl oyster Pinctada mazatlanica ofthe American Pacific coasts have been considered endangeredbecause of overfishing and/or alteration to coastal areas. Weassessed genetic variability and the pattern of populationstructure among 9 samples collected from Mexico to Panama, usingmtDNA RFLP analysis of two genes: 12S rRNA and subunit one ofCytochrome oxydase (COI). Haplotype diversity varied from 0.000to 0.856. The Panama population appeared to be monomorphic, whilethe other samples exhibited a level of haplotypic variabilitysimilar to those reported in the literature for the same kind ofanalysis on other bivalves species. A test for the impact ofdemographic history on genetic diversity was applied on thesequence data, and the results were congruent with a recentdecline of population sizes. Genetic differentiation was shown tofollow a scheme of isolation by distance, with low levels ofdifferentiation at the scales of ten to one hundred kilometres,whereas stronger and significant genetic structure was detectedat a larger scale. Three significantly distinct groups could thenbe defined, which correspond to Northern Mexico, Southern Mexico,and Panama.