Identifying the true oysters (Bivalvia: Ostreidae) with mitochondrial phylogeny and distance‐based DNA barcoding

Abstract

Oysters (family Ostreidae), with high levels of phenotypic plasticity and wide geographic distribution, are a challenging group for taxonomists and phylogenetics. As a useful tool for molecular species identification, DNA barcoding might offer significant potential for oyster identification and taxonomy. This study used two mitochondrial fragments, cytochrome c oxidase I (COI) and the large ribosomal subunit (16S rDNA), to assess whether oyster species could be identified by phylogeny and distance-based DNA barcoding techniques. Relationships among species were estimated by the phylogenetic analyses of both genes, and then pairwise inter- and intraspecific genetic divergences were assessed. Species forming well-differentiated clades in the molecular phylogenies were identical for both genes even when the closely related species were included. Intraspecific variability of 16S rDNA overlapped with interspecific divergence. However, average intra- and interspecific genetic divergences for COI were 0-1.4% (maximum 2.2%) and 2.6-32.2% (minimum 2.2%), respectively, indicating the existence of a barcoding gap. These results confirm the efficacy of species identification in oysters via DNA barcodes and phylogenetic analysis.

Mitochondrial DNA and morphological identification of a new cupped oyster speciesCrassostrea dianbaiensis(Bivalvia: Ostreidae) in the South China Sea

“…1) found in Wenchang, Hainan province by Liu et al (2011) should be recognized as C. dianbaiensis because these two taxa share almost identical cox1 sequences.…”

“…from Canela Island was shown to be more similar to Indo-Pacific oysters, and either arrived in the Atlantic Ocean before the convergence of the Isthmus of Panama or was accidentally brought to Brazil by ship. In the study of Liu et al (2011), a total of five unassigned Indo-Pacific species were identified, including two Crassostrea (C. sp. 1; C. sp.…”

“…Similarly, using mitochondrial DNA sequences, Wang et al (2010) recommended that the Pacific oyster (C. gigas) and the Portuguese oyster (C. angulata) should be referred to as two subspecies under the name of C. gigas (C. gigas gigas and C. gigas angulate, respectively). Studies concerning molecular identification, phylogeny and investigations of geographic distribution have been performed for Crassostrea oysters throughout the world Liu et al 2011), in countries such as South America (de Melo et al 2010), Thailand (Bussarawit 2003), China (Xia et al 2009;Wu et al 2010) and Asia .…”

“…Based on the shape of the shell, the oyster is one of the most variable bivalves in the world (Gunter 1950), and therefore, morphology is of limited value for species identification and taxonomy de Melo et al 2010). Crassostrea oysters are widespread and the most commercially important group of oysters, and hence have received more attention concerning their taxonomy, phylogeny and population genetics (Lam and Morton 2003;Reece et al 2008;Liu et al 2011;Li et al 2013;Wu et al 2013). Currently, a total of 35 Crassostrea oysters have been confirmed by professional taxonomists and listed in taxonomic databases such as WoRMS (World Register of Marine Species, http://www.marinespecies.…”

“…The unassigned species Crassostrea sp. 2 in the study of Liu et al (2011) might be C. zhanjiangensis, a newly described Indo-Pacific oyster, based on the nearly identical 16S rRNA sequences of these two species . Meanwhile, the phylogenetic status of the unassigned species Crassostrea sp.…”