Substantial asexual recruitment of mushroom corals contributes little to population genetics of adults in conditions of chronic sedimentation

Abstract

The contribution of asexual versus sexual recruitment to populations of the mushroom coral Fungia fungites was investigated at 2 sites with contrasting sediment regimes, located 5 km apart in the Dampier Archipelago (Western Australia). One site was exposed to high levels of chronic sedimentation, and many of its F. fungites polyps were asexual buds attached to dead parent polyps. A total of 95 buds were sampled from 26 parent skeletons; all buds on each parent were of the same genotype. The second site received less than half the sediment load, and the F. fungites polyps there were not observed to produce asexual buds. I hypothesised that asexual and sexual recruitment would contribute disproportionately to the maintenance of the high- and low-sediment sites respectively. However, electrophoretic analysis of 7 polymorphic loci indicated that sexual recruitment was responsible for the majority of adults in a random sample (n = 120) of polyps from each site. All polyps sampled at the low-sediment site had unique 7 locus genotypes. Between 10 and 30% of the polyps at the sediment-affected site were derived asexually, but all were in juvenile size classes, usually as replicate buds attached to a single parent. No adult polyps shared the same genotype, despite evidence that rarely, some asexual recruits may survive to adult size. Patterns of sexual recruitment underlying both populations were characterised by major heterozygote deficiencies and considerable inbreeding (F IS = 0.571 ± 0.018 SE). Most genetic differentiation occurred between locations within sites (F ST = 0.080) rather that among sites (F ST = 0.022). Dispersal of gametes and larvae appear to be highly localised.