A new phylogeny for Scleractinia
Kannan Mahadevan
One of the benefits of the EOL’s many content-sharing agreements is that it stays current by association. Take the case of scleractinian corals, which were the subject of an EOL synthesis meeting from June 15-19 at the Smithsonian Natural History Museum in Washington D.C. The order Scleractinia, or ‘stony corals,’ includes reef-building corals, which in the words of the meeting’s proposal, undergirds “the most diverse of all marine ecosystems, tropical shallow-water reefs (Paulay 1997), with estimates of associated species numbers ranging from 1-9 million (Reaka-Kudla 1997).” And yet, the evolution and systematics of this ecologically crucial group are still fundamentally misunderstood: traditional phylogenies of scleractinian corals based on macromorphological characters have yet to be reconciled with those produced by more current molecular data. In sponsoring a meeting designed to work towards solving this discrepancy, the EOL’s Biodiversity Synthesis Group effectively ensured that the EOL would eventually inherit a reworked, up-to-date phylogeny of scleractinian corals.
Featuring an international presence—17 participants representing six different countries (the U.S., U.K., Spain, France, the Netherlands, and Poland)—the meeting marked the collaboration of a team of experts whose collective expertise encompassed the taxonomy of both living and fossil scleractinian corals. After giving individual talks, the participants divided into more focused break-out groups, each assigned to tackle different sections of the phylogeny of scleractinian corals.
The meeting made significant progress on two interlinked fronts: reworking the phylogeny of scleractinian corals to include all forms, from Triassic to living, and constructing a morphological character matrix to delineate micromorphological traits that better reflect molecular results than traditional macromorphological ones. The first goal followed directly from the gathering of marine biologists, who do phylogenetics research on living taxa using molecular and/or morphologic data, with paleontologists, who study long-term evolutionary history using fossils. Such synthesis guaranteed that a unified phylogeny would include fossil taxa.
As the second front—isolating new morphological characters—was begun almost from scratch, it took quite a lot of work for break-out groups to get through even a couple of their assigned families. Combing through images, the participants tried to pick up on microstructural and micromorphological features that could be said to distinguish different genera. Often, their attention was drawn to septa—calcified, radially-aligned elements that make up the skeleton of a scleractinian polyp—whose shape they described with such makeshift terms as “fan-shaped” or “paddle-shaped.” Yet these rough-and-ready descriptions laid the groundwork for a classification scheme, both by training scientists to know what traits to look for in the future, and by establishing morphological character states that will later serve as standards to determine type specimens. In fact, quantifying subjective characters to come up with a morphological character matrix was set as a topic for an upcoming meeting involving many of the same participants.
Lastly, the meeting cemented a content-sharing agreement between the EOL and Corallosphere, an online database featuring nomenclatural and descriptive information for around 1600 nominal scleractinian genera. In addition to sharing existing species descriptions and images with Corallosphere, the EOL would ultimately inherit the new classification scheme and pages for corresponding type specimens, directly authored by participants identified at the meeting. This new phylogeny has the potential to reset conservation efforts that aim to preserve major branches of the scleractinian evolutionary tree. For example, the finding that the dominant reef-building corals of the Atlantic and Pacific come from different lineages—based on molecular rather than conventional macromorphological data, which held the two groups to be monophyletic—identified evolutionary distinctiveness as a conservation priority to be considered along with “diversity and endemicity at the species level” (For more information, see Fukami, H., A.F. Budd, G. Paulay, A. Solé-Cava, C.A. Chen, K. Iwao, and N. Knowlton. 2004. Conventional Taxonomy Obscures Deep Divergence between Pacific and Atlantic Corals. Nature 427: 832-835). In any case, regardless of its future implications for conservation, commitment to a new classification scheme constitutes a significant first step for the coral community as well as the EOL.
