Genetic structure of the exotic hard clam Mercenaria mercenaria in Tokyo Bay, determined using mitochondrial DNA

Abstract

The hard clam Mercenaria mercenaria was unintentionally introduced into Tokyo Bay during the 1990s. We analysed 528 bp of partial mitochondrial DNA of the cytochrome c oxidase subunit 1 (COI) gene extracted from 135 specimens collected from populations at five sites in Tokyo Bay to determine the genetic structure of this species. Mercenaria mercenaria populations in Tokyo Bay were dominated by haplotype 1, as in the native area. Haplotype 3, which is absent in the populations north of Cape Hatteras (North Carolina, USA) was detected at all five sites. The haplotype diversity in Tokyo Bay was as high as that in the native area, except at two canal sites, while the nucleotide diversity was lower. Thirty-five new haplotypes were found that displayed only a few nucleotide differences. Pairwise F ST values were not significantly different between any sites in the Tokyo Bay and the east coast of America, with values for all sites in Tokyo Bay clustering near the Florida populations. The analysis of molecular variance (AMOVA) results also support this result. This study revealed that M. mercenaria populations in Tokyo Bay have a high haplotype diversity and that populations around Florida may be the source region.