Genetic and morphological differentiation in the hermatypic coral Galaxea fascicularis in Okinawa, Japan

Abstract

Galaxea fascicularis is a common reef-building coral in the Indo-Pacific area including the Ryukyu Archipelago. A previous study on nematocyst morphology and mitochondrial genotype suggested that G. fascicularis consists of two genetically differentiated groups. However, the extent of the reproductive barrier between the two groups remains unknown. In the present study, more than 99% of G. fascicularis colonies were classified into two groups based on allelic difference of a nuclear microsatellite locus. Colonies exhibiting the hybrid genotype were rare (only two out of 224 colonies), suggesting that the reproductive barrier between the groups is nearly impermeable. The two groups were highly correlated to different nematocyst types and mitochondrial haplotypes, supporting the previous hypothesis that G. fascicularis consists of two genetically and morphologically differentiated lineages in the Ryukyu Archipelago. However, the frequencies of six color morphs were rather similar between the two groups, indicating that the evolution of the color variation had occurred before the divergence of G. fascicularis into the two lineages.