Exploring Canadian Echinoderm Diversity through DNA Barcodes

Abstract

DNA barcoding has proven an effective tool for species identification in varied groups of marine invertebrates including crustaceans, molluscs, polychaetes and echinoderms. In this study, we further validate its utility by analyzing almost half of the 300 species of Echinodermata known from Canadian waters. COI sequences from 999 specimens were assigned to 145 BINs. In most cases, species discrimination was straightforward due to the large difference (25-fold) between mean intra- (0.48%) and inter- (12.0%) specific divergence. Six species were flagged for further taxonomic investigation because specimens assigned to them fell into two or three discrete sequence clusters. The potential influence of larval dispersal capacity and glacial events on patterns of genetic diversity is discussed for 19 trans-oceanic species. Although additional research is needed to clarify biogeographic patterns and resolve taxonomic questions, this study represents an important step in the assembly of a DNA barcode library for all Canadian echinoderms, a valuable resource for future biosurveillance programs.

Fig 1. Sampling map.

Collection localities and sample sizes for 999 specimens that generated a COI sequence in this study.

Fig 2. Barcode gap.

Nearest-Neighbor distances (% K2P) plotted against maximum intraspecific divergences (% K2P) for 113 taxa with two or more individuals. All taxa show a barcode gap.

Fig 3. Relationship between COI distance and sample size.

Maximum and mean intraspecific divergences (% K2P) plotted against the number of individuals sampled for 113 species. The regression between maximum intraspecific divergence and the number of individuals sampled is significant (R² = 0.089, p<0.01).

Fig 4. Depth partitioning in Lophaster furcilliger.

Maximum-likelihood tree (HKY+I) for specimens of Lophaster furcilliger from British Columbia. Groups A, B and C are partitioned by depth and sequence number is presented in brackets for each clade. Scale bar represents percent sequence divergence.

Fig 5. Deep divergences at COI within Henricia.

Maximum-likelihood tree (GTR+G+I) for 16 putative species of Henricia. Locality information is provided for each lineage (Atl = Atlantic, Arc = Arctic, Pac = Pacific) and sequence number is presented in brackets for each clade. Scale bar represents percent sequence divergence.

Fig 6. Divergences at COI for three echinoderm species.

Maximum-likelihood (HKY+I) trees illustrating population structure at COI in three species of Canadian echinoderms: A) Crossaster papposus, B) Pteraster militaris and C) Solaster endeca. Sequence number is presented in brackets for each clade. Scale bars represent percent sequence divergence.