The evolutionary history of the coral genus Acropora (Scleractinia, Cnidaria) based on a mitochondrial and a nuclear marker: Reticulation, incompletelineage sorting, or morphological convergence?

This study examines molecular relationships across a wide range of species in the mass spawning scleractinian coral genus Acropora. Molecular phylogen ies were obtained for 28 species using DNA sequence analyses of two indepen dent markers, a nuclear intron and the mtDNA putative control region. Altho ugh the compositions of the major clades in the phylogenies based on these two markers were similar, there were several important differences. This, i n combination with the fact that many species were not monophyletic, sugges ts either that introgressive hybridization is occurring or that lineage sor ting is incomplete. The molecular tree topologies bear little similarity to the results of a recent cladistic analysis based on skeletal morphology an d are at odds with the fossil record. We hypothesize that these conflicting results may be due to the same morphology having evolved independently mor e than once in Acropora and/or the occurrence of extensive interspecific hy bridization and introgression in combination with morphology being determin ed by a small number of genes. Our results indicate that many Acropora spec ies belong to a species complex or syngameon and that morphology has little predictive value with regard to syngameon composition. Morphological speci es in the genus often do not correspond to genetically distinct evolutionar y units. Instead, species that differ in timing of gamete release tend to c onstitute genetically distinct clades.