Content area
Full text
Fish Sci (2013) 79:6176DOI 10.1007/s12562-012-0577-2
ORIGINAL ARTICLE Biology
Mitochondrial DNA barcoding for Okinawan oysters: a cryptic population of the Portuguese oyster Crassostrea angulatain Japanese waters
Masashi Sekino Hiroyoshi Yamashita
Received: 21 September 2012 / Accepted: 31 October 2012 / Published online: 5 December 2012 The Japanese Society of Fisheries Science 2012
Abstract We used mitochondrial (mt) DNA barcoding to evaluate the species diversity of oysters sampled from the coast of Okinawa Island, Japan. Our analysis revealed the presence of a hitherto-unrecognized population of the Portuguese oyster Crassostrea angulata, a putative species closely related to the Pacic oyster C. gigas. Forty-eight Okinawan oyster specimens were collected and subjected to species diagnosis trials based on mtDNA barcodes. Of the 30 Crassostrea specimens, 17 were identied as C. angulata, seven as C. gigas and six as C. bilineata (syn. C. iredalei). The remaining 18 Saccostrea specimens formed several divergent clades in phylogenetic trees, although they could not be identied to species level because of the confounding taxonomy of the Saccostrea species complex. Our results stress the necessity for reviewing the species diversity of Okinawan oysters.
Keywords Species diagnosis Taxonomic uncertainty
Cytochrome c oxidase subunit I Ostreidae Saccostrea
Species complex
Introduction
A prerequisite for undertaking projects aimed at promoting the appropriate management of biodiversity is the correct identication of organisms at the species level. In oyster species, the highly variable nature of their phenotypic characteristics makes it notoriously difcult to discriminate between closely related species based on morphology alone [1], often resulting in an incorrect allocation of different species into a single taxon [2]. The advent of molecular diagnostic tools capable of identifying organisms to the species level has therefore facilitated taxonomic and ecological studies of oysters, enabling the resolution of taxonomic confusion [13] and the discovery of cryptic populations of species [4].
Okinawa Main Island, Japan, is a subtropical island and the largest island in the Ryukyu (Nansei) Archipelago (Fig. 1). The island chain of Ryukyu is characterized by its unique biota and distinctive ecosystems, which have been formed through the long-term terrestrial disjunctions of the component islands from other larger lands that surround the East China Sea [5]. However, many animals within the irreplaceable fauna are threatened with extinction by habitat contractions caused by recent land/coastal reclamations,...