Mitochondrial phylogeography of a surf clam Mactra veneriformis in the East China Sea: Genetic homogeneity across two biogeographic boundaries

Abstract

Biogeographic boundaries constraining species' distributions often generate intraspecific ‘breaks’ for those species whose ranges span them—known as the ‘biogeography-phylogeography concordance’ hypothesis. The East China Sea (ECS) in the northwestern Pacific comprises two reported boundaries: the Shandong Peninsula and the Changjiang Estuary, providing an elegant setting to test the hypothesis in marine environment. Here we investigated population structure of the surf clam Mactra veneriformis (Reeve, 1854) using 235 individuals from its major distribution in the ECS, represented by mitochondrial cytochrome oxidase I sequences. A ‘star-like’ topology with shallow divergence was revealed for all haplotypes, of which the central (also assumed ancestral) one appearing in all populations. No significant genetic structure was revealed among populations, suggesting substantial genetic homogeneity across the range. Demographic expansion was revealed for individual and overall populations, and the expansion time was estimated from 23,000 years ago. These results suggested that the M. veneriformis populations originated from an ancestral panmictic population in the ECS basin, and had experienced significant population expansion since the last glacial maximum. From a mitochondrial view, the two boundaries did not act as barriers for the phylogeography of M. veneriformis.