Models of Reticulate Evolution in the Coral Genus Acropora Based on Chromosome Numbers: Parallels With Plants

Somatic chromosome number was determined for 22 species of the scleractinian coral genus Acropora, three species of Montipora, and one species of Fungia, using colchicine-treated cells of externally developing embryos. Most had 28 chromosomes, except for six species of Acropora, which had somatic numbers of 24, 30, 30, 42, 48, and 54. Two models that invoke a combination of polyploidy and aneuploidy are presented to account for the observed intrageneric variation in somatic chromosome number. The ability to propagate clones through vegetative fragmentation plus the opportunities for hybridization during multispecies spawning events may have contributed to the development of polyploidy and rapid, sympatric speciation in the uniquely speciose coral genus Acropora.