HYBRIDIZATION WITHIN THE SPECIES COMPLEX OF THE SCLERACTINAN CORAL MONTASTRAEA-ANNULARIS

The morphologically variable reef coral previously known as Montastrae a annularis (Ellis and Solander, 1786) has recently been separated int o three species based on differences in morphology, behavior, allele f requencies and some life-history traits of Panamanian specimens. To fu rther investigate the proposed reclassification and its conformity to the biological species concept we conducted reciprocal intra-and inter -specific fertilization experiments with gametes from each of the thre e species on Florida reefs. With one exception, self-fertilization rat es were very low or zero. Within-species crosses resulted in productio n of planulae, as did all inter-species (hybrid) crosses, but there wa s much variation in fertilization success within each type of cross. I n an experiment with separated gametes, hybrid crosses between M. annu laris is and M. franksi produced more larvae than within-species cross es for each species. Hybridization crosses between M. faveolata and th e other two species produced fewer larvae than did within-M. faveolata crosses in the experiment with separated gametes, but many larvae res ulted when the hybridizations were performed by mixing entire gamete b undles. Additional observations showed that M. franksi had 20% larger eggs and fewer eggs per gamete bundle than did the other two species a nd that it consistently spawned to 1.5 h before the others, a potentia l temporal barrier to hybridization. These results indicate that there is no inherent pre-zygotic barrier to cross-fertilization among the t hree morphological species, although post-zygotic survival and fertili ty remain to be determined. The adherence of the proposed reclassifica tion to the biological species concept requires further examination.