Longterm Patterns of Morphological Variation within and Among Species of Reef-Corals and their Relationship to Sexual Reproduction

Patterns of morphological variation were compared among clades of scleractinian reef-corals, which differ in degree of sexuality, to determine if species discreteness and cohesiveness differ between predominantly biparental and predominantly uniparental reproducers. First, canonical discriminant analysis and sheared principal component analyses were used to analyze morphological variation within and among local populations of species of Porites, Siderastrea, and Montastraea from environmentally distinct habitats near Discovery Bay, Jamaica. The results show that variation is reduced within populations of Montastraea annularis and Porites astreoides, two species which frequently reproduce uniparentally. No clear relationship was found between degree of outcrossing and differentiation among populations. Next, to compare discreteness of species, similar analyses were made among living species within these clades. The results suggest that species are more discrete in the biparental genus Siderastrea and less discrete in eastern Pacific Pocillopora, a genus in which reproduction is largely uniparental. Analyses of fossils of these genera from the Neogene of the Dominican Republic confirm that species are more discrete in Siderastrea. Multivariate analyses of temporal variation within each species through the five million year Dominican Republic sequence, as well as over the past 30 million years throughout the Caribbean, further show that stasis appears to be the rule regardless of degree of outcrossing. Thus, despite clonal population structures, coral species do form discrete evolutionary units over geologic time. Lastly, clade diversity within any one time interval was found to be roughly comparable in biparental and uniparental reproducers, although speciation and extinction rates appear slightly higher in uniparental clades in association with extinction events. In conclusion, other than possible reduced divergence during speciation, uniparental reproduction appears to have little longterm influence on the phylogenies of these corals.