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.

Genetic differentiation and connectivity of morphological types of the broadcast‐spawning coral Galaxea fascicularis in the Nansei Islands, Japan

“…Although mt-L colonies were more numerous than mt-S colonies, the ratio of types varies widely among the sites that we sampled. This pattern agrees with the previous studies (Watanabe et al 2005;Abe et al 2008a). All sites, excluding A-Kat, possessed both types, and the ratio is unrelated to latitude in the Nansei Islands.…”

“…; Abe et al. ). All sites, excluding A‐Kat, possessed both types, and the ratio is unrelated to latitude in the Nansei Islands.…”

“…; Abe et al. ). Significant genetic differentiation between these mt‐Long (mt‐L) and mt‐Short (mt‐S) types was shown at Zampa, on Okinawa Island using polymorphic nuclear microsatellite markers (Nakajima et al.…”

“…It is a gonochoric, broadcast-spawning species; female colonies produce egg bundles, and male colonies form bundles consisting of sperm and infertile pseudo-eggs (e.g., Harrison 1988;Hayakawa et al 2007;Keshavmurthy et al 2012). This species is classified into soft and hard types based on nematocyst morphology (Hidaka 1992), and this morphological characteristic is correlated with the length of the noncoding region between the mitochondrial genes cyt b and nad 2 (mt-Long: soft type; mt-Short: hard type) (Watanabe et al 2005;Abe et al 2008a). Significant genetic differentiation between these mt-Long (mt-L) and mt-Short (mt-S) types was shown at Zampa, on Okinawa Island using polymorphic nuclear microsatellite markers (Nakajima et al 2015).…”

Breeding experiments of hermatypic coralGalaxea fascicularis: partial reproductive isolation between colonies of different nematocyst types and enhancement of fertilization success by presence of parental colonies

“…In most G. fascicularis colonies, only one of the two MpM types is found in external tentacles, although a small number of individuals possess a mixture of the S and H types 7,8 . Molecular analyses have shown that the MpM types are highly correlated to different genotypes in a mitochondrial intergenic region 8 and at a nuclear microsatellite locus 9 . Thus, this species in Okinawa is suspected to consist of two reproductive units that occur in sympatry.…”