ASEXUAL FRAGMENTATION, GENOTYPE SUCCESS, AND POPULATION-DYNAMICS OF ERECT BRANCHING SPONGES

Three common species of erect branching sponges on Caribbean coral reefs propagate almost exclusively by asexual fragmentation. Fragments are generated frequently, are able to disperse before establishing themselves as independent individuals, survive well, and are responsible for virtually all successful recruitment into their populations. With respect to numbers of individuals, populations are dominated by smaller size classes, reflecting continuous generation of small individuals by fragmentation of large individuals. Because specific growth rates of these sponges decrease with increasing size, fragmentation is predicted to be the preferred strategy for increasing representation of a genotype in the population as long as mortality associated with fragmentation is not high. Fragment dispersal obviates several of the usual constraints on frequency of a genotype in a population by ensuring local genotypic heterogeneity in spite of low overall genotypic diversity in the populations.