A mega-cryptic species complex hidden among one of the most common annelids in the North East Atlantic

<div><p>We investigate mitochondrial (<i>COI</i>, <i>16S rDNA</i>) and nuclear (<i>ITS2</i>, <i>28S rDNA</i>) genetic structure of North East Atlantic lineages of <i>Terebellides</i>, a genus of sedentary annelids mainly inhabiting continental shelf and slope sediments. We demonstrate the presence of more than 25 species of which only seven are formally described. Species boundaries are determined with molecular data using a broad range of analytical methods. Many of the new species are common and wide spread, and the majority of the species are found in sympatry with several other species in the complex. Being one of the most regularly encountered annelid taxa in the North East Atlantic, it is more likely to find an undescribed species of <i>Terebellides</i> than a described one.</p></div

A mega-cryptic species complex hidden among one of the most common annelids in the North East Atlantic - Fig 1

<p>Live specimens of A) <i>Terebellides williamsae</i> (specimen 2181_2), in lateral view, with oocytes in the coelomic cavity and B) species 7 (specimen 2448_7), in lateral view. <i>Abbreviations</i>: ab (abdomen), bl (branchial lamellae), br (branchiae), bs (branchial stalk), bt (buccal tentacles), gc (geniculate chaetae), ll (lateral lappets), tr (thorax).</p

Depth distribution for collecting sites, including number of sites and specimens for each biogeographic region.

<p>Scale is logarithmic.</p

Results from the phylogenetic analyses, summarized on the ML estimate of the combined data set with xinsi-aligned ITS2-sequences including 91 terminals.

<p>Specimens are named according to the extraction-number and the appended clade-number. The phylogenetic tree is arbitrarily divided into four colour-coded groups, A–D. These colours are used as background colour in the distribution and haplotype network figures (Figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198356#pone.0198356.g006" target="_blank">6</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198356#pone.0198356.g008" target="_blank">8</a>). Specimens with at least three of the genetic markers were included in the phylogenetic analyses, outgroups are not shown. Pie diagrams indicate support values for the node, left pie shows results from ML analyses, and right pie diagram results from Bayesian analyses. Upper two slices of a pie illustrate results from the combined data sets' two different alignments, with xinsi-aligned ITS2-sequences to the left, and salsa-aligned ITS2-sequences to the right. The three remaining slices illustrate results from the combined mitochondrial data (lower left slice), and the combined nuclear data sets' two different alignments, where lower median slice has xinsi-aligned ITS2-sequences, and lower right slice has salsa-aligned ITS2-sequences. Yellow, blue and red colour indicate low, moderate and strong support, which equals ML support in the intervals 50–74, 75–89, and 90–100, or BI posterior probabilities in the intervals 0.50–0.84, 0.85–0.94 and 0.95–1.0 respectively. White means support <50/0.50 for the node. Columns show clustering of terminals according to different methodologies performed on more inclusive data sets where all specimens with COI or ITS2 data, or specimens with both COI and ITS2 data, were included. The first columns under the headings COI, ITSx and ITSs represent the results from TCS, and the second columns represent the results from GMYC. The columns under the heading STACEY show the two different outcomes from this analysis. White means that the network or species recovered is identical to the initial haplotype network found in COI including all COI-sequences, light grey means that less inclusive networks or putative species were recovered, and dark grey means that a more inclusive network or putative species was recovered. Double-headed arrows to the right of the columns show our final judgement of species delimitation. The two small letters to the right indicate our designation of described species, st = <i>T</i>. <i>stroemii</i>, bi = <i>T</i>. <i>bigeniculatus</i>, at = <i>T</i>. <i>atlantis</i>, sh = <i>T</i>. <i>shetlandica</i>, ir = <i>T</i>. <i>irinae</i>, wi = <i>T</i>. <i>williamsae</i>, and gr = <i>T</i>. <i>gracilis</i>.</p

Diagram showing the distribution of different <i>Terebellides</i> species in the ten biogeographic regions.

<p>Diagram showing the distribution of different <i>Terebellides</i> species in the ten biogeographic regions.</p

Collecting sites, biogeographic regions, and type localities for <i>Terebellides irinae</i> (ir), <i>T</i>. <i>atlantis</i> (at), <i>T</i>. <i>bigeniculatus</i> (bi), <i>T</i>. <i>shetlandica</i> (sh), <i>T</i>. <i>williamsae</i> (wi), <i>T</i>. <i>stroemii</i> (st), and <i>T</i>. <i>gracilis</i> (gr) indicated with an arrow.

<p>Type localities for <i>T</i>. <i>irinae</i> and <i>T</i>. <i>atlantis</i> are located outside the map's area. Biogeographic regions given by colours of samples (collecting sites) (see text for definitions): <i>Kattegat</i> (magenta); <i>Skagerrak</i> (dark green); <i>North Sea</i> (light green); <i>Irish Sea</i>, <i>Celtic Sea</i> (orange); <i>Norwegian coast and shelf</i> (red); <i>Norwegian Sea</i> (brown); <i>Barents Sea</i> (dark blue); <i>Arctic Ocean</i> (rose red); <i>Greenland Sea</i> (yellow); <i>South of Iceland</i> (light blue).</p

A mega-cryptic species complex hidden among one of the most common annelids in the North East Atlantic - Fig 7

<p>Distribution maps, depth distribution in meters, and haplotype networks for group A, species 6, 7, 8, and 9, and for group B, species 1, 17, 14, 4, 26, and 27. All species except for species 6 that we refer to as <i>T</i>. <i>stroemii</i> (st), and clade 1 that we refer to as <i>T</i>. <i>shetlandica</i> (sh) are undescribed. Sites are colour coded as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198356#pone.0198356.g003" target="_blank">Fig 3</a>. Type localities for <i>T</i>. <i>stroemii</i>, and <i>T</i>. <i>shetlandica</i> indicated with yellow arrows.</p

Summary of haplotype and distance analyses for ITS2, with specification of excluded sequences, alignment length, number of haplotypes, and uncorrected intra- and interspecific distances.

<p>Species number to which the species is compared with, for the minimum and maximum interspecific distances, in parentheses.</p

Summary of haplotype and distance analyses for COI, with specification of excluded sequences, alignment length, number of haplotypes, and uncorrected intra- and interspecific distances.

<p>Species number to which the species is compared with, for the minimum and maximum interspecific distances, in parentheses.</p

Locality and collecting data, including sample size, and species sampled.

<p>Locality and collecting data, including sample size, and species sampled.</p