Molecular and Morphological Species Boundaries in the Gorgonian Octocoral Genus Pterogorgia (Octocorallia: Gorgoniidae)

PLoS One. 2015 Jul 21;10(7):e0133517. doi: 10.1371/journal.pone.0133517. eCollection 2015.

Abstract

Most gorgonian octocoral species are described using diagnostic characteristics of their sclerites (microscopic skeletal components). Species in the genus Pterogorgia, however, are separated primarily by differences in their calyx and branch morphology. Specimens of a morphologically unusual Pterogorgia collected from Saba Bank in the NE Caribbean Sea were found with calyx morphology similar to P. citrina and branch morphology similar to P. guadalupensis. In order to test morphological species boundaries, and the validity of calyx and branch morphology as systematic characters, a phylogenetic analysis was undertaken utilizing partial gene fragments of three mitochondrial (mtMutS, cytochrome b, and igr4; 726bp total) and two nuclear (ITS2, 166bp; and SRP54 intron, 143bp) loci. The datasets for nuclear and mitochondrial loci contained few phylogenetically informative sites, and tree topologies did not resolve any of the morphological species as monophyletic groups. Instead, the mitochondrial loci and SRP54 each recovered two clades but were slightly incongruent, with a few individuals of P. guadalupensis represented in both clades with SRP54. A concatenated dataset of these loci grouped all P. anceps and P. guadalupensis in a clade, and P. citrina and the Pterogorgia sp. from Saba Bank in a sister clade, but with minimal variation/resolution within each clade. However, in common with other octocoral taxa, the limited genetic variation may not have been able to resolve whether branch variation represents intraspecific variation or separate species. Therefore, these results suggest that there are at least two phylogenetic lineages of Pterogorgia at the species level, and the atypical Pterogorgia sp. may represent an unusual morphotype of P. citrina, possibly endemic to Saba Bank. Branch morphology does not appear to be a reliable morphological character to differentiate Pterogorgia species (e.g., branches "flat" or "3-4 edges" in P. guadalupensis and P. anceps, respectively), and a re-evaluation of species-level characters (e.g., sclerites) is needed.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Anthozoa
  • Base Sequence
  • Cnidaria / anatomy & histology
  • Cnidaria / classification
  • Cnidaria / genetics*
  • DNA, Mitochondrial / genetics*
  • Genetic Loci
  • Genetic Variation
  • Introns
  • Molecular Sequence Data
  • Phylogeny*

Substances

  • DNA, Mitochondrial

Associated data

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Grants and funding

This work was supported by the U.S. National Science Foundation OCE-0527184 to ACB and Rowlands and Knight Graduate Fellowships, University of Miami to HHW. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.