Examination of the Montastraea annularis species complex (Cnidaria : Scleractinia) using ITS and COI sequences

The Caribbean coral Montastraea annularis has recently been proposed to be a complex of at least three sibling species. To test the validity of this p roposal, we sequenced the ITS region of the nuclear ribosomal RNA gene fami ly (ITS-1, 5.8S, and ITS-2), and a portion of the mitochondrial DNA gene cy tochrome c oxidase subunit I (COI) from the three proposed species (M. annu laris, M. faveolata, and M. franksi) from Florida reefs. The ITS fragment w as 665 nucleotides long and had 19 variable sites, of which 6 were parsimon y-informative sites. None of these sites was fixed within the proposed spec ies. The COI fragment nas 658 nucleotides long with only two sites variable in one individual. Thus, under both the biological species concept and the phylogenetic species concept, the molecular evidence gathered in this stud y indicates the Montastraea annularis species complex to be a single evolut ionary entity as opposed to three distinct species. The three proposed Mont astraea species can interbreed, ruling out prezygotic barriers to gene now (biological species concept), and the criterion of monophyly is not satisfi ed if hybridization is occurring among taxa (phylogenetic species concept).