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Abstract

HYBRIDIZATION DYNAMICS IN THE THREATENED CARIBBEAN CORAL GENUS, ACROPORA

Nicole D. Fogarty
Florida State University
Bio

Since the 1970’s, Caribbean acroporids have decreased by 80-98% prompting their enlistment as threatened under the Endangered Species Act. Caribbean acroporids consist of two species, A. palmata and A. cervicornis, which form a hybrid (A. prolifera). Although hybrids were not given protective status, they may play an important ecological and evolutionary role in the fate of this reef-building genus. At sites throughout the Caribbean where both parent species are present, hybrid abundance forms a continuum from absent or rare to dense stands. It is unclear if this variation in abundance occurs as a result of differences in the strength of reproductive isolating barriers, variation in success of asexual fragmentation, or differential fitness (i.e. susceptibility to disease, predation, and bleaching) of hybrids. Carrie Bow Island, Belize has a population of at least 75 hybrid colonies. Molecular analysis at six loci showed that these colonies are composed of two genets that have fragmented and reattached in this shallow (< 1m) turbulent habitat. A. palmata and A. cervicornis gametes were collected in situ during a simultaneous spawning event. Fertilization and viability experiments revealed that there is no statistical difference in fertilization success, larval survival, or metamorphosis between conspecific and heterospecific crosses. Gamete comparisons of one hybrid colony with the parent species showed hybrids have larger eggs, less sperm and an intermediate number of eggs per bundle. Preliminary analysis suggests these hybrids host a different zooxanthellae clade that may allow them to persist in this extremely shallow, stressful environment. Despite low genetic diversity among the Carrie Bow hybrids, the population is robust due to the hybrid’s ability to persist and reproduce asexually in a stressful habitat. Further, these hybrids are fertile and capable of producing an F2 generation or backcrossing with the parent species, which may lead to genetic introgression between the parent species.