Data from: The curious case of Hermodice carunculata (Annelida: Amphinomidae): evidence for genetic homogeneity throughout the Atlantic Ocean and adjacent basins

Over the last few decades, advances in molecular techniques have led to the detection of strong geographic population structure and cryptic speciation in many benthic marine taxa, even those with long-lived pelagic larval stages. Polychaete annelids, in particular, generally show a high degree of population divergence, especially in mitochondrial genes. Rarely have molecular studies confirmed the presence of ‘cosmopolitan’ species. The amphinomid polychaete Hermodice carunculata was long considered the sole species within its genus, with a reported distribution throughout the Atlantic and adjacent basins. However, recent studies have indicated morphological differences, primarily in the number of branchial filaments, between the East and West Atlantic populations; these differences were invoked to re-instate Hermodice nigrolineata, formerly considered a junior synonym of H. carunculata. We utilized sequence data from two mitochondrial (cytochrome c oxidase subunit I, 16S rDNA) markers and one nuclear (internal transcribed spacer) marker to examine the genetic diversity of Hermodice throughout its distribution range in the Atlantic Ocean, including the Mediterranean Sea, the Caribbean Sea, the Gulf of Mexico and the Gulf of Guinea. Our analyses revealed generally low genetic divergences among collecting localities and between the East and West Atlantic, although phylogenetic trees based on mitochondrial data indicate the presence of a private lineage in the Mediterranean Sea. A re-evaluation of the number of branchial filaments confirmed differences between East and West Atlantic populations; however, the differences were not diagnostic and did not reflect the observed genetic population structure. Rather, we suspect that the number of branchial filaments is a function of oxygen saturation in the environment. Our results do not support the distinction between H. carunculata in the West Atlantic and H. nigrolineata in the East Atlantic. Instead, they re-affirm the older notion that H. carunculata is a cohesive species with a broad distribution across the Atlantic Ocean.近数十年来，分子技术的进步使得研究者得以在诸多底栖海洋类群（benthic marine taxa）中检测到显著的地理种群结构与隐存物种形成，即便是那些拥有长寿命浮游幼体阶段的类群亦不例外。多毛类环节动物（polychaete annelids）的种群分化程度普遍较高，在线粒体基因层面尤为显著，鲜有分子研究能证实广布种（cosmopolitan species）的存在。 磷沙蚕科（Amphinomidae）多毛类动物Hermodice carunculata长期以来被认为是其所在属内的唯一物种，报道分布范围覆盖大西洋及邻近海域。然而近期研究显示，大西洋东西两侧种群在鳃丝数量等形态特征上存在差异，这些差异被用于恢复曾被视为H. carunculata同物异名的Hermodice nigrolineata的物种地位。 本研究利用两个线粒体标记基因——细胞色素c氧化酶亚基I（cytochrome c oxidase subunit I）与16S核糖体DNA（16S rDNA），以及一个核标记基因——内转录间隔区（internal transcribed spacer），对大西洋海域（包括地中海、加勒比海、墨西哥湾及几内亚湾）内Hermodice属动物的分布范围开展遗传多样性分析。 研究结果显示，各采样点之间以及大西洋东西两侧种群的遗传分化程度普遍较低；不过基于线粒体数据构建的系统发育树显示，地中海海域存在一支特有谱系。对鳃丝数量的重新评估证实了大西洋东西两侧种群间确实存在形态差异，但该差异并不具备分类诊断价值，亦未反映观测到的遗传种群结构。相反，我们推测鳃丝数量受环境中氧饱和度的影响。 本研究结果不支持西大西洋H. carunculata与东大西洋H. nigrolineata的物种划分，反而进一步证实了此前的学术观点：H. carunculata是一个遗传上统一、分布范围横跨整个大西洋海域的广布物种。