Estimation of mating systems in Short and Tall ecomorphs of the coral Favia fragum.

We used 15 microsatellite markers to estimate the selfing rate (s), outcrossing rate (t(O) ) and hybridization between partially sympatric ecomorphs (t(H) ) of the coral Favia fragum. Genotyping of progeny arrays revealed complete self-fertilization in the Tall ecomorph and low outcrossing (t(O)  + t(H)  < 1%) in the Short ecomorph. Further, all larvae could be assigned with high probability to the same population as their parental dam, indicating no hybridization between ecomorphs (t(H)  = 0). Despite low ecological estimates of outcrossing, Q values from highly structured adult populations indicated that 9% of the adult samples were the products of outcrossing, and an additional 11% were hybrids. Reproductive isolation appears to have a strong geographical component, as we did not detect hybrids at a second site where the two ecomorphs were distributed in complete microallopatry. Adult estimates of gene flow within ecomorphs may be positively biased by ecomorph-specific patterns of inbreeding depression, but cryptic gene flow between ecomorphs is most likely explained by undetected outcrossing and the fact that hybrid lineages persist after repeated generations of self-fertilization. Our microsatellite data show that phenotypic differences between ecomorphs are maintained in sympatry despite evidence for hybridization.