Genetic Variation in Released Gametes Produces Genetic Diversity in the Offspring of the Broadcast Spawning Coral Acropora Tenuis

All coral species in the genus Acropora are broadcast-spawning hermaphrodites. Fertilization in the ocean requires sufficient numbers of gametes from conspecifics and the contact time for fertilization is thought to be limited by the rapid diffusion of sperm. Many studies have reported a positive correlation between sperm concentration and fertilization success, but it is not clear how released gametes are fertilized in nature (in situ) and how genetic diversity arises at a fertilization event. To elucidate this, we analyzed the changes in sperm concentration in situ after spawning and genotyped sperm and fertilized eggs from seawater using seven microsatellite (MS) markers. This showed that the sperm concentration in situ was suboptimal (<106 sperm/mL), but most of the eggs were fertilized. MS genotyping showed that the alleles of released sperm were diverse and those alleles also appeared in the fertilized eggs. In addition, the MS fragment peak height in released sperm, which presumable reflects the allele frequency of the sperm, was positively correlated with the allele frequencies of the fertilized eggs. Collectively, the genetic diversity of colonies with high fecundity dictates the genetic diversity of their descendants.