Phylogeography and Taxonomic Revision of the Pen Shell Atrina pectinata Species Complex in the South China Sea

Abstract

Phylogeographic studies contribute to addressing questions regarding the geographic patterns and evolutionary scenarios within and among species and also shed light on the taxonomic status of widely distributed species complexes. The pen shell Atrina pectinata species complex is a widely distributed and economically important bivalve in the northwestern Pacific. Previous phylogeographic studies have identified four genetically distinct cryptic species within the A. pectinata species complex along the coast of China, of which three cryptic species were distributed in the South China Sea. However, less attention has been given to their identification and delimitation. Herein, we report the phylogeography and taxonomic revision of the A. pectinata species complex in the South China Sea using DNA sequence data from mitochondrial cytochrome oxidase I (COI) and 16S ribosomal RNA (16S rRNA), and nuclear 28S ribosomal RNA (28S rRNA) gene markers. Using a combination of phylogenetic and DNA-based species delimitation analysis methods, we found strong support for four genetically valid species in the A. pectinata species complex and defined them as A. japonica, A. lischkeana, Atrina sp., and A. pectinata based on our results as well as on previous morphological and genetic studies. A demographic historical analysis showed that all three species in the South China Sea had populations that were relatively stable over time and then subjected to sudden expansion during the late Pleistocene (60,000–90,000 years ago). These results provide new insights into the systematics and evolution of the A. pectinata species complex and have important conservation and management implications.

Introgressive hybridization in the west Pacific pen shells (genus Atrina): Restricted interspecies gene flow within the genome

“…Based on the definition of the six mitochondrial lineages, the primary A. pectinata lineages in Japanese waters are L1 and L2 (we refer to the lineages as mt‐L1 and mt‐L2), which correspond to the nonscaly and scaly forms of A. pectinata , respectively (Hashimoto et al, 2018, 2021). We treat hereafter the two lineages as different species, presuming that the lineage mt‐L1 represents Atrina japonica (Reeve, 1858), and the lineage mt‐L2, Atrina lischkeana (Clessin, 1891), according to suggestions by many authors (Huber, 2010; Japanese Association of Benthology, 2012; Kurozumi, 2017; Schultz & Huber, 2013; Xue et al, 2021). Both A. japonica and A. lischkeana typically occur in inner bays (low tidal zones to the depth of 30 m; Japanese Association of Benthology, 2012), but A. japonica is found in higher latitudes than is A. lischkeana with some exceptions (Hashimoto et al, 2021; Liu et al, 2011; Xue et al, 2021).…”

“…Japanese Association of Benthology, 2012), but A. japonica is found in higher latitudes than is A. lischkeana with some exceptions (Hashimoto et al, 2021;Liu et al, 2011;Xue et al, 2021). Allopatric A. japonica and A. lischkeana can be distinguished by assessing if their shells are finely ribbed and spinous (Figure 2).…”

“…In the past, there were implications that discernible Atrina morphotypes should be synonymized en masse with A. pectinata (e.g., Rosewater, 1961). The entity of the nominal A. pectinata is nonetheless unclear, as the Atrina morphotypes have variously been classified (Hashimoto et al, 2018(Hashimoto et al, , 2021Liu et al, 2011;Xue et al, 2012Xue et al, , 2021). An isozyme-based survey in the Seto Inland Sea (Japan; Figure 1) indicated a large genetic divergence between sympatric population samples of a "nonscaly" form of A. pectinata, which bears a smooth outer shell surface, and a "scaly" form with fine ribs and densely packed spines (or scaly protrusions) on its shell surface (Yokogawa, 1996; see Figure 2).…”