Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

Self-compatible, hermaphroditic marine invertebrates have the potential to self-fertilize in the absence of mates or under sperm-limited conditions, and outcross when sperm is available from a variety of males. Hence, many hermaphroditic marine invertebrates may have evolved mixed-mating systems that involve facultative self-fertilization. Such mixed-mating strategies are well documented for plants but have rarely been investigated in animals. Here, I use allozyme markers to make estimates of selfing from population surveys of reef slope and reef flat sites, and contrast this with direct estimates of selfing from progeny-array analysis, for the brooding coral Seriatopora hystrix. Consistent heterozygote deficits previously reported for S. hystrix suggests that inbreeding (including the extreme of selfing) may be common in this species. I detected significant levels of inbreeding within populations (FIS=0.48) and small but significant differentiation among all sites (FST=0.04). I detected no significant differentiation among habitats (FHT=0.009) though among site differentiation did occur within the reef slope habitat (FSH=0.06), but not within the reef flat habitat (FSH=0.015). My direct estimates of outcrossing for six colonies and their progeny from a single reef flat site revealed an intermediate value (tm (±s.d.)=0.53±0.20). Inbreeding coefficients calculated from progeny arrays (Fe=0.31) were similar to indirect estimates based on adult genotype frequencies for that site (FIS=0.38). This study confirms that the mating system of this brooding coral is potentially variable, with both outcrossing and selfing.