DIRECT EVIDENCE FOR REPRODUCTIVE ISOLATION AMONG THE 3 SPECIES OF THEMONTASTRAEA-ANNULARIS COMPLEX IN CENTRAL-AMERICA (PANAMA AND HONDURAS)

Montastraea annularis, M. faveolata, and M. franksi are three recently separated species that together dominate reefs of the tropical wester n Atlantic. Despite morphological, life-history, ecological and geneti c differences, the legitimacy of their status as separate species has been questioned. This controversy stems from both the scarcity of unam biguous, diagnostic differences among them, and from the possibility o f extensive hybridization associated with their approximately synchron ous reproduction in sympatry. Here we report on fertilization trials a nd the timing of spawning, both of which suggest that the potential fo r hybridization may be limited. Crosses between M. faveolata (the most genetically distinctive taxon) and the other two species were largely unsuccessful, as were selfed matings for all three species. M. annula ris is and M. franksi showed no evidence of fertilization barriers, bu t the timing of spawning typically differed between them by 1 to 2 h. We also found that spawning times in the field of M. annularis and M. faveolata were non-overlapping in 1995, and that the timing of spawnin g in M. annularis could be experimentally shifted forward by simulatin g earlier than natural sunsets. These findings from Panama and Hondura s, particularly given their consistency with comparable observations a nd experiments elsewhere, provide evidence of reproductive isolation a nd support the separate species status of these three taxa. Some hybri dization may occur under natural conditions at these sites, particular ly between M. annularis and M. franksi. Rampant genetic interchange am ong these taxa in Central America seems unlikely, however, in the ligh t of the concordant associations between morphology, reproductive biol ogy and other characters which are observed.