Family Tree Shake-Up for Threatened Reef-building Corals

For more than a half century, scientists have drawn and redrawn the branches of the complex and ambiguous family tree illustrating the ancestry of reef-building coral species. Evidence is mounting that many traditional assumptions about these relationships are wrong. A new genetic study by an international team of experts looking at an array of coral species from around the world has shown that major revisions are in order. The results of their research appear in the Sept. 16 issue of the Public Library of Science’s PLoS ONE.

“The scale of the shake-up is unprecedented,” said Nancy Knowlton, the Sant Chair for Marine Science at the Smithsonian’s National Museum of Natural History and a co-author of the paper. “It would be like learning that many of your cousins were family imposters, and many complete strangers were actually your close relatives.”

By analyzing the DNA of 127 species of corals, the researchers conducted the most comprehensive and definitive investigation to date of evolutionary relationships among hard corals. Comparing the 19 groupings they uncovered with 17 traditional families of reef-building corals, they found that only one family had retained all its original members. Four new branches were uncovered, and nine of the groupings joined members of two, three or four traditional families. Five traditional families were not only disbanded, but contained corals from opposite ends of the new coral tree.

While initially surprised by some of their findings, the researchers found that in many cases, physical features of the corals, when closely examined, agreed with the DNA evidence.

“Many of the features are microscopic, and are observable only due to advances in microscopic technology over the past two decades,” said Ann Budd, a co-author of the paper from the University of Iowa. Previous studies, they found, also had ignored some important physical clues linking related species.

“Our findings highlight the importance of multidisciplinary approaches linking genetics and morphology for the future” said Allen Chen, a co-author of the paper from Biodiversity Research Centre, Academia Sinica, Taiwan.

The researchers also collected evidence against the recent suggestion that one group of corals with no skeleton (known as “naked corals”) might have evolved from hard corals and then lost their skeletons. Instead, genetic sequencing suggested that the naked corals evolved separately and belonged on a different branch of the evolutionary tree.

“This highlights one of the fundamental strengths of science, that prior assertions are continually tested by new data,” said Allen Collins of the National Marine Fisheries Service and the National Museum of Natural History, a co-author on this and an earlier study contradicted by this one.

In addition to setting the ancestral record straight, the research could have implications for coral conservation efforts. Knowing which corals are closely related and which are not will help scientists better predict the types of corals that are at risk and those that are likely to be resilient in the face of climate change, overfishing and other human disturbances.

“Such knowledge is critical to preserving major branches of the coral family tree, a task made more urgent by recent estimates that a staggering one-third of all corals are threatened by extinction,” said Knowlton.

The paper appears in the Sept. 16 issue of the Public Library of Science’s PLoS ONE, available at http://dx.plos.org/10.1371/journal.pone.0003222.

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SI-407-2008