Short-term Visitor

Understanding the role of coloniality and photosymbiosis in coral macroevolution

PI(s): Carl Simpson (Museum fuer Naturkunde, Leibniz Institute at the Humboldt University Berlin )
Start Date: 22-Jun-2011
End Date: 19-Aug-2011
Keywords: macroevolution, biodiversity, natural selection, coevoution, climate change

What are the contributions and consequences of the coral-zoxanthellae mutualism to the patterns of scleractinian coral macroevolution? Mutualisms are advantageous for the organisms involved but their macroevolutionary consequences are not generally known. The photosymbiotic zooxanthellate (Z) and non-photosymbiotic azooxanthellate (AZ) corals originate together in the Triassic and today are equally diverse, suggesting that photosymbiosis has no net advantage over long timescales. Corals have a rich fossil record showing that Z corals diversify early and decline in diversity toward the Recent, while AZ corals steadily increase in diversity. Z corals suffered greater losses during the end-Cretaceous extinction. One possible explanation for the apparent macroevolutionary trade-off, is that zooxanthellae restrict their hosts to living in shallow tropical seas. AZ corals have no such restriction, but their deep sea occurrences may be under represented in the fossil record. To understand how photosymbiosis influences macroevolution, the temporal patterns of coral diversification, extinction, and habitat range of Z and AZ corals must be described using molecular phylogenetics in combination with paleontological analyses. While visiting NESCent I will identify temporal patterns in (1) the association of photosymbiosis with extinction, speciation, and net diversification rates using both fossil and molecular approaches, and (2) the acquisition and loss of photosymbiosis, using an already compiled dataset consisting of fossil and recent occurrences supplemented with a comprehensive time-calibrated molecular phylogeny of scleractinians.