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Low endemism, continued deep-shallow interchanges, and evidence for cosmopolitan distributions in free-living marine nematodes (order Enoplida)

Lunt, David H.; Bik, Holly M.; Lambshead, P. John D.; Thomas, W. Kelley


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Dr Dave Lunt
Head, Biological Sciences Subject Group

Holly M. Bik

P. John D. Lambshead

W. Kelley Thomas


Background: Nematodes represent the most abundant benthic metazoa in one of the largest habitats on earth, the deep sea. Characterizing major patterns of biodiversity within this dominant group is a critical step towards understanding evolutionary patterns across this vast ecosystem. The present study has aimed to place deep-sea nematode species into a phylogenetic framework, investigate relationships between shallow water and deep-sea taxa, and elucidate phylogeographic patterns amongst the deep-sea fauna. Results: Molecular data (18 S and 28 S rRNA) confirms a high diversity amongst deep-sea Enoplids. There is no evidence for endemic deep-sea lineages in Maximum Likelihood or Bayesian phylogenies, and Enoplids do not cluster according to depth or geographic location. Tree topologies suggest frequent interchanges between deep-sea and shallow water habitats, as well as a mixture of early radiations and more recently derived lineages amongst deep-sea taxa. This study also provides convincing evidence of cosmopolitan marine species, recovering a subset of Oncholaimid nematodes with identical gene sequences (18 S, 28 S and cox1) at trans-Atlantic sample sites. Conclusions: The complex clade structures recovered within the Enoplida support a high global species richness for marine nematodes, with phylogeographic patterns suggesting the existence of closely related, globally distributed species complexes in the deep sea. True cosmopolitan species may additionally exist within this group, potentially driven by specific life history traits of Enoplids. Although this investigation aimed to intensively sample nematodes from the order Enoplida, specimens were only identified down to genus (at best) and our sampling regime focused on an infinitesimal small fraction of the deep-sea floor. Future nematode studies should incorporate an extended sample set covering a wide depth range (shelf, bathyal, and abyssal sites), utilize additional genetic loci (e.g. mtDNA) that are informative at the species level, and apply high-throughput sequencing methods to fully assay community diversity. Finally, further molecular studies are needed to determine whether phylogeographic patterns observed in Enoplids are common across other ubiquitous marine groups (e. g. Chromadorida, Monhysterida).

Journal Article Type Article
Publication Date Dec 1, 2010
Journal BMC evolutionary biology
Print ISSN 1471-2148
Electronic ISSN 1471-2148
Publisher BioMed Central
Peer Reviewed Peer Reviewed
Volume 10
Issue 1
Pages 389
Keywords Pellioditis marina; Atlantic Ocean; Sequence data; Sea isopods; Gene flow; Meiofauna; Oxygen; DNA; Biodiversity; Dispersal
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Copyright Statement © Bik et al; licensee BioMed Central Ltd. 2010
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Additional Information Copy of article first published in BMC evolutionary biology, 2010, issue 389, v.10


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