Clonal distribution and spatial genetic structure of the reef-building coral Galaxea fascicularis

Abstract

Genotypic distributions affect the persistence of coral populations, and mapping these distributions is important for population management. Many studies have examined genetic connectivity among sites, but within-site spatial genotypic patterns based on clonal distribution and kinship are poorly understood. Such patterns are an important index for understanding the potential for population recovery at small spatial scales. Here, we studied within-reef spatial genotypic distributions and clonality of a broadcast-spawning coral, Galaxea fascicularis, by using mitochondrial DNA (mtDNA) and 15 nuclear microsatellite markers. Specimens were collected at shallow reefs (< 3 m) at four sites in the Ryukyu Archipelago, Japan. Among 289 colonies analyzed, we detected two common mtDNA types (mt-L, 174 colonies; mt-S, 113 colonies) and one rare type (mt-L + , 2 colonies). The proportion of duplicate clonal colonies differed across sites and reef topographies; the maximum distance between clonemates was approximately 120 m. Pairwise kinship among colonies tended to decrease with distance at the ramet level (i.e., including clonal replicates), but not at the genet level. Ramet-level kinship varied among sites rather than between mtDNA types. Genet-level kinship (i.e., excluding clonal replicates) was similar among sites. These results for clonality and kinship suggest that both sexual and asexual reproduction contribute to population recovery after disturbances and maintain genetic diversity in local populations. However, the extent of sexual and asexual reproduction differs across sites. Our results will contribute to more effective management of marine reserves by emphasizing the importance of clonal distributions and genetic kinship at each reef site.