Abstract
Marine nematodes, which play an important role in many ecosystems, include a number of apparently cosmopolitan taxa that exhibit broad biogeographic ranges even though there is no obvious dispersal phase in their lifecycle. In this study, standard taxonomic approaches to marine nematode identification in conjunction with multivariate statistical analysis of morphometric data were compared with molecular techniques. Specimens of the marine nematode Terschellingia longicaudata that had been identified by their morphological features were investigated from a range of localities (East and West Atlantic, Bahrain, Malaysia) and habitats (estuarine, intertidal, subtidal) using molecular approaches based on the amplification and sequencing of the small subunit ribosomal RNA (18S rRNA). The study revealed that the majority of the morphologically defined T. longicaudata specimens share a single 18S rRNA sequence and apparently belong to a single taxon distributed from the British Isles to Malaysia. In addition, 18S rRNA analysis also revealed two additional sequences. One of these sequences was found in both the British Isles and Mexico, the other was recorded only from British waters. Individuals collected in Bahrain and identified from their morphology as T. longicaudata had two highly divergent 18S rRNA sequences. Separate morphological and morphometric approaches to identification of specimens from the same sites that had been formalin-preserved did not support evidence of multiple genotypes revealed previously by molecular analysis. Current taxonomy based on morphological characters detected using light-microscopy may be unable to discriminate possible species complexes. Biodiversity of marine nematodes may often be underestimated due to the presence of morphologically cryptic species complexes. High-throughput techniques such as DNA barcoding would aid in species identification but may require thorough analysis of multiple nuclear and mitochondrial molecular markers.
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Acknowledgments
Punyasloke Bhadury acknowledges Plymouth Marine Laboratory (PML) for the provision of a Ph.D. Studentship. The authors would like to thank Hazel Needham, Sarah Dashfield and Andrea McEvoy for help with the taxonomic identification, and Paul Somerfield, Michaela Schratzberger and Rachel Jones for providing nematode specimens. The authors wish to thank the three anonymous reviewers for their help in improving this manuscript. This is a contribution to the PML Biodiversity and Sustainable Ecosystems project. The authors acknowledge the support by the MarBEF Network of Excellence ‘Marine Biodiversity and Ecosystem Functioning’ which is funded by the Sustainable Development, Global Change and Ecosystems Programme of the European Community’s Sixth Framework Programme (contract no. GOCE-CT-2003-505446).
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Communicated by S. Uthicke.
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Bhadury, P., Austen, M.C., Bilton, D.T. et al. Evaluation of combined morphological and molecular techniques for marine nematode (Terschellingia spp.) identification. Mar Biol 154, 509–518 (2008). https://doi.org/10.1007/s00227-008-0945-8
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DOI: https://doi.org/10.1007/s00227-008-0945-8