Biodiversity Institute of Ontario, University of Guelph, Guelph, Ontario, Canada.
PLoS One. 2011;6(7):e22232. doi: 10.1371/journal.pone.0022232. Epub 2011 Jul 14.
Although polychaetes are one of the dominant taxa in marine communities, their distributions and taxonomic diversity are poorly understood. Recent studies have shown that many species thought to have broad distributions are actually a complex of allied species. In Canada, 12% of polychaete species are thought to occur in Atlantic, Arctic, and Pacific Oceans, but the extent of gene flow among their populations has not been tested.
METHODOLOGY/PRINCIPAL FINDINGS: Sequence variation in a segment of the mitochondrial cytochrome c oxidase I (COI) gene was employed to compare morphological versus molecular diversity estimates, to examine gene flow among populations of widespread species, and to explore connectivity patterns among Canada's three oceans. Analysis of 1876 specimens, representing 333 provisional species, revealed 40 times more sequence divergence between than within species (16.5% versus 0.38%). Genetic data suggest that one quarter of previously recognized species actually include two or more divergent lineages, indicating that richness in this region is currently underestimated. Few species with a tri-oceanic distribution showed genetic cohesion. Instead, large genetic breaks occur between Pacific and Atlantic-Arctic lineages, suggesting their long-term separation. High connectivity among Arctic and Atlantic regions and low connectivity with the Pacific further supports the conclusion that Canadian polychaetes are partitioned into two distinct faunas.
CONCLUSIONS/SIGNIFICANCE: Results of this study confirm that COI sequences are an effective tool for species identification in polychaetes, and suggest that DNA barcoding will aid the recognition of species overlooked by the current taxonomic system. The consistent geographic structuring within presumed widespread species suggests that historical range fragmentation during the Pleistocene ultimately increased Canadian polychaete diversity and that the coastal British Columbia fauna played a minor role in Arctic recolonization following deglaciation. This study highlights the value of DNA barcoding for providing rapid insights into species distributions and biogeographic patterns in understudied groups.
尽管多毛类动物是海洋生物群落中的主要类群之一，但它们的分布和分类多样性仍知之甚少。最近的研究表明，许多被认为分布广泛的物种实际上是相关物种的复合体。在加拿大，有 12%的多毛类物种被认为分布在大西洋、北极和太平洋，但它们的种群之间的基因流动程度尚未得到检验。
方法/主要发现：线粒体细胞色素 c 氧化酶 I（COI）基因的一段序列变异被用来比较形态与分子多样性估计，研究广泛分布物种的种群之间的基因流动，并探索加拿大三个海洋之间的连通模式。对代表 333 个暂定物种的 1876 个标本的分析显示，种间序列差异是种内差异的 40 倍（16.5%比 0.38%）。遗传数据表明，四分之一的先前公认的物种实际上包含两个或更多的分歧谱系，这表明该地区的丰富度目前被低估了。具有三洋分布的少数物种显示出遗传凝聚力。相反，太平洋和大西洋-北极谱系之间存在较大的遗传断裂，表明它们长期分离。北极和大西洋地区之间的高度连通性和与太平洋的低连通性进一步支持了加拿大多毛类动物被分为两个不同动物群的结论。
结论/意义：本研究的结果证实，COI 序列是多毛类动物物种鉴定的有效工具，并表明 DNA 条形码将有助于识别当前分类系统中忽略的物种。在假定广泛分布的物种中，一致的地理结构表明，在更新世期间，历史范围的碎片化最终增加了加拿大多毛类动物的多样性，并且冰川消融后，不列颠哥伦比亚省沿海的动物群在北极的重新殖民化中发挥了次要作用。本研究强调了 DNA 条形码在提供对研究较少的群体的物种分布和生物地理模式的快速了解方面的价值。
