Genetic evidence for mixed modes of reproduction in the coral Pocillopora damicornis and its effect on population structure

Allozyme electrophoresis of 6 polymorphic loci was used to estimate the relative importance of sexual and asexual reproduction in Western Australian populations of the coral Pocillopora damicornis and to infer the extent of larval dispersal between them. Evidence for considerable yet variable amounts of asexual reproduction was found, Only 96 of a total of 644 coral heads sampled were apparently of sexual origin, and 8 of the 10 populations showed large departures from HardyWeinberg equilibria as a result of both heterozygote excesses and deficits. Multi-locus genotypic diversity values were significantly less than expected for 8 of the 10 Populations sampled, but the magnitude of these values varied enormously (range G(0):G(e) = 0.072 to 0.770). Significant genetic subdivision among populations was found (F-ST = 0.360) that was not attributable to different reefs (F-RT = 0.080), habitat type (F-HT = -0.039), or geographical distance between populations (Mantel test p = 0.129). However, pairwise comparisons revealed significant genetic subdivision at all spatial scales sampled. Furthermore, this subdivision was largely maintained even among populations of putative sexual origin (F-ST = 0.175). These results are consistent with the notion that reefs at Ningaloo and the Houtman Abrolhos Islands are primarily self-seeding and that asexually derived recruits have a considerable effect on local abundance and population structure.