Sexual dimorphism in corallite size and modularity of a broadcast spawning coral, Porites lobata

Differences in selective pressures and the energetic cost of gametes in gonochoristic corals should vary with the sex of the colony, which may lead to sexual dimorphism. Coral colonies are composed of subunits (corallites) that create a complex morphological architecture. If corallite features are distinct between sexes, then the degree of coordinated change among these subunits may also vary (phenotypic modularity). This study tested for sexual dimorphism in the corallites of the reef-building coral Porites lobata, a gonochoric broadcast spawner, and compared this with previously demonstrated sexual dimorphism in its congener P. panamensis, a gonochoric brooder. Corallite area in P. lobata was 17% larger for males than for females (p < 0.05). Phenotypic modularity analysis showed that the integration of skeletal traits differs between sexes in both P. lobata and in P. panamensis. In P. lobata, females showed a higher trait integration than males, while the opposite pattern was observed in P. panamensis. Our results demonstrate corallite traits differentiate between sexes and suggest that between-sex differences in the degree of corallite integration may vary with reproductive mode.