BackgroundAlthough 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 FindingsSequence 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/SignificanceResults 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.

Phylogenetic relationships within Serpulidae (Sabellida, Annelida) inferred from molecular and morphological data. -Zoologica Scripta , 35 , 421-439. We assessed phylogenetic relationships within Serpulidae (including Spirorbinae) using parsimony and Bayesian analyses of 18S rDNA, the D1 and D9 − D10 regions of 28S rDNA, and 38 morphological characters. In total, 857 parsimony informative characters were used for 31 terminals, 29 serpulids and sabellid and sabellariid outgroups. Following ILD assessment the two sequence partitions and morphology were analysed separately and in combination. The morphological parsimony analysis was congruent with the results of the 2003 preliminary analysis by Kupriyanova in suggesting that a monophyletic Serpulinae and Spirorbinae form a clade, while the remaining serpulids form a basal grade comprising what are normally regarded as Filograninae. Bremer support values were, however, quite low throughout. In contrast, the combined analyses of molecular and morphological data sets provided highly resolved and well-supported trees, though with some conflict when compared to the morphologyonly analysis. Spirorbinae was recovered as a sister group to a monophyletic group comprising both 'filogranin' taxa ( Salmacina , Filograna , Protis , and Protula ) and 'serpulin' taxa such as Chitinopoma , Metavermilia , and Vermiliopsis . Thus the traditionally formulated subfamilies Serpulinae and Filograninae are not monophyletic. This indicates that a major revision of serpulid taxonomy is needed at the more inclusive taxonomic levels. We refrain from doing so based on the present analyses since we feel that further taxon sampling and molecular sequencing are required. The evolution of features such as the operculum and larval development are discussed.

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Disturbed ecosystems often exhibit increased community heterogeneity when compared to nondisturbed systems. One way to measure community heterogeneity is statistical dispersion, a measure of how variable individual samples are from the multivariate average of the community condition (species presence/absence and density). In more specific manner, dispersion measures the distance between an individual data point and the centroid, the multivariate average of all data points. Statistical dispersion may be an important parameter to include in environmental assessments, or in studies that attempt to understand the role of disturbances in structuring biological systems. However, disturbances have been observed to increase, decrease, or not impact community dispersion (or community heterogeneity). Therefore, the usefulness of dispersion in studying or identifying disturbances is unclear. We tested if a mechanical disturbance increased community dispersion using the infaunal community of the intertidal mudflats along the north coast of British Columbia, Canada. We observed no statistically significant increase in community dispersion with varying frequency and intensity of a mechanical disturbance. This is likely a result of disturbed and nondisturbed treatments being dominated by the same six taxa, thus minimizing dispersion. Therefore, in ecosystems where differences in community successional stages are subtle (a result of changes in relative abundance rather than species replacement), community dispersion may not be an informative parameter when investigating disturbance. Despite this, we suggest that dispersion can be a useful variable to include in studies attempting to understand or identify disturbances; however, dispersion should only be one parameter amongst many used to understand or identify disturbances.

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