Genetic evidence for the existence of cryptic species in an endangered clam Coelomactra antiquata

Abstract

Coelomactra antiquata is a commercially important bivalve species, but has been suffering from severe population decline due to over-exploitation and the deterioration of environmental conditions. Previous genetic survey of C. antiquata conducted with allozymes combined with morphology revealed high levels of genetic differentiation between northern and southern populations which suggests a cryptic species might exist in C. antiquata. To test this hypothesis, amplified fragment length polymorphisms (AFLPs) and 16S rRNA gene sequence were used to re-evaluate the spatial genetic structure of six populations of C. antiquata along the coast of China. Both genetic markers display a sharp genetic break between the four northern populations (northern lineage) and two southern population (southern lineage). Large numbers of private alleles (AFLP) were found within the northern or southern populations and a deep divergence of about 6.5% in 16S rRNA gene sequence between the northern and southern lineages suggests the occurrence of potential cryptic or sibling species of C. antiquata. Applying previously published rates of mutation, divergence between the two lineages is estimated to have occurred approximately 3 million years ago and may be due to allopatric isolation during the middle Pliocene times. While no genetic differentiation was found within the northern or southern populations in both AFLP and 16S mtDNA markers, the results indicate that the northern and southern lineage should be managed separately and any translocation between the two areas should be avoided.