Nuclear and mitochondrial gene sequences reveal unexpected genetic heterogeneity among northern Pacific populations of the brachiopod Lingula anatina

Abstract

The geographic population structure of sequence variations in a cox1 region of mitochondrial DNA and an intron region of the nuclear EF-1α gene has been assessed for the brachiopod Lingula anatina from three northern Pacific localities, namely Mutsu Bay (northern Japan), Ariake Sea (southern Japan), and Hong Kong. Both the mitochondrial and nuclear gene genealogies indicated a clear separation of the three populations with no shared haplotypes between them, and a sister group relationship between the Mutsu and Ariake haplotypes, each of which formed a monophyletic cluster. Statistical reanalysis of published allozyme data demonstrated genetic divergence between the Mutsu and Ariake populations and between Australian and Japanese populations. Morphometry of shell dimensions also discriminated between forms of the Mutsu and Ariake populations. Those observations gainsay the prevailing hypothesis that populations of L. anatina maintain panmixia and a single homogeneous gene pool over the entire Indo-West Pacific region, and suggest that each population of Mutsu, Ariake, and by inference also Hong Kong, could be seen as a separate species.