Genetic Divergence And Phylogeography Of Macridiscus In The Northwestern Pacific

The genus Macridiscus, which contains M. melanaegis, M. multifarious and M.semicancellata, is widely distributed along the coast of the eastern Asia. Phylogeneticand phylogeographic analysis of Macridiscus were conducted by mitochondrial andnuclear DNA sequences. The genetic patterns were discussed to assess the relativeeffects of historical, contemporary and ecological factors on shaping the presentphylogeographical patterns of each species. The information obtained here will behelpful for the conservation of the marine mollusk resources.1. Genetic structure and phylogeography of Macridiscus genusThere are a series of marginal seas with unique terrain and complicated hydrologyalong the northwestern Pacific. Two hypotheses have been proposed to explain thegenetic difference and the geography patterns of marine species inhabiting the region.Fragments of mtCOI and nrITS were sequenced for265individuals collected from16populations. Molecular markers both proved that there were three species in the genusMacridiscus, which was in accordance with the result of morphological classification.The divergence times dated from the Plio-Pleistocene epochs according to theanalysis of molecular clock among the three species. Historical demography showedthat all species had experienced significant population expansions. Significantdifferences were observed between different marginal sea populations in M.melanaegis and M. multifarious, however, no significant differences were found in the populations of M. semicancellata. The historical isolation of sea basins probablyplayed a major role in diversities of the Macridiscus species. The dispersal ability ofthe larvae and the current maintained Macridiscus species widely distributing in thenorthwestern Pacific.2. Isolation and characterization of14microsatellite loci in Macridiscussemicancellata (Koch in Philippi,1843)The first set of14polymorphic microsatellite loci were isolated and characterizedin Macridiscus semicancellata. Number of alleles per polymorphic locus varied from4to12. The observed and expected heterozygosities ranged from0.233to0.758andfrom0.244to0.880, respectively. These informative markers obtained in this studywill offer useful tools for the assessment of population structure and gene flow of thespecies in the future.