1Graduate School of Bioresources, Mie University, Tsu, Mie 514-8507, Japan
The freshwater clams, Corbicula leana Prime, 1864. and C. fluminea (Müller, 1774) are native and exotic androgenetic hermaphrodites in Japan, respectively. Since the early 1980s, C. fluminea has been repeatedly introduced from East Asia throughout Japan. To elucidate the relationship between the two species, we examined their phenotypes, ploidy, and nucleotide sequence of mitochondrial DNA (mtDNA) cytochrome b (Cyt b) gene. Although the clams were classified into three phenotypes (C. leana, and green and yellow types in C. fluminea) by shell morphology, both diploid and triploid were observed in all phenotypes. In the phylogenetic tree based on the Cyt b sequences, two major clades were recognized, which did not correspond to phenotype or ploidy. In addition, the same dominant haplotype was commonly observed in the three phenotypes. These results unambiguously indicate that C. leana and C. fluminea are genetically indistinguishable, casting doubt on the validity of their taxonomic status.