Meeting Abstract

S8.5  Wednesday, Jan. 6  Phylogenetics and morphological evolution in Scleractinian corals BARBEITOS, MS*; ROMANO, SL; LASKER, HR; University of Kansas; University of the Virgin Islands; University at Buffalo msbb@ku.edu

Over recent years, molecular phylogenetic analyses have repeatedly made it clear that Scleractinian taxonomy does not reflect phylogenetic relationships within the order. Pervasive plasticity of skeletal characters and evolutionary convergence make it very difficult to assess homology in traditional diagnostic characters. Here, we review the current understanding of relationships within Scleractinia and expand on previous results by sampling extensively among azooxanthellate lineages, which account for more than half of extant coral richness. We used partial sequences of two rRNA genes (mitochondrial 12S and nuclear 28S) for phylogenetic reconstructions. Phylogenetic accuracy was enhanced by incorporating a Cnidaria-wide putative secondary structure model in our alignment, thus improving assessment of positional homology, and also by using evolutionary models that account for lack of independence among nucleotides due to compensatory mutations in stem regions. We uncovered well supported sister relationships among several reef and deep-water corals and also a previously ignored link between reef corals of the Western Atlantic and azooxanthellate lineages of the Eastern Atlantic/Mediterranean. Ancestral character state reconstruction revealed that at least three solitary, azooxanthellate lineages descend from colonial ancestors. In the light of paleontological evidence that reefs have waxed and waned continuously during the Phanerozoic, we hypothesize that loss of coloniality via heterochrony may have allowed some lineages to overcome periods of widespread extinction due to reef recession.