Testing the effectiveness of the mt DNA Cytochrome c oxidase subunit 1 (COI) gene locus for identifying species of Polychaete worm (Polychaeta: Annelida) in New Zealand

Abstract

The ability to accurately identify species is fundamental to ecological research and environmental monitoring. Current taxonomic identifications often rely on differentiation of morphologically ambiguous characters, and a process of categorization which is tedious and often leads to misidentifications. This is compounded by the presence of cryptic taxa, which may be prevalent among Polychaete worms (Polychaeta: Annelida). With increased access to genetic techniques, Cytochrome c oxidase subunit I has been suggested as a possible aid to assist in the discrimination of species resources. In this study, I tested the hypothesis that the mtDNA COI gene locus is effective in discriminating morphologically recognised species of Polychaete worms. A 543 base-pair fragment of the COI locus was successfully extracted for 111 individuals from 16 out of 20 morphologically recognised species. Average intraspecific divergences were 0.8 %, ranging from 0 % to 5 %. Average interspecific variation was 26.4 %, ranging from 13.8 % to 36.8 %. The lowest divergences were found between two Nereid species (13.8 %), and two Glycera americana species (17.2 %). Relatively high maximum divergences of over 30 % suggest that some species may have reached a divergence saturation level, which may partially explain why familial groupings in constructed trees were not monophyletic. Divergences within the different Nereid species - a group previously known to have morphologically cryptic species - did not reveal the presence of any cryptic taxa. Pairwise comparisons showed a clear divide between percentages of intra- and interspecific divergences, and the suggested threshold of 11 % is effective for the taxa investigated here. On the basis of these results, I conclude that sequence variation in the mtDNA COI gene locus is effective in discriminating morphologically recognised species of Polychaete worms, but may not be appropriate for deeper (e.g. generic or familial) phylogenetic relationships among taxa.