Abstract
Okinawa Island is located near the center of the Nansei Islands (∼24–31°N), at a relatively high latitude for coral reefs. Nevertheless, more than 80 coral genera (over 400 species) are abundant in the Nansei Islands. Since March, 2017, scleractinian corals have been held in an outdoor tank at the OIST Marine Science Station at Seragaki, Onna with natural sea water flow-through in order to be used in molecular biological and physiological studies. In January, 2018, we found small pocilloporid-like colonies suspected to have originated asexually. We collected 25 small colonies and measured their sizes and weights. Also, we validated the classification and clonality of the colonies using a mitochondrial locus and nine microsatellite loci. Almost all of the small colonies collected in the outdoor tank were ≤1 cm in both width and height. The weight of dried skeletons ranged from 0.0287 to 0.1807 g. Genetic analysis determined that they were, in fact, Pocillopora acuta. Only one mitochondrial haplotype was shared and two microsatellite multilocus genotypes were detected (20 colonies of one and four colonies of the other). The mitochondrial haplotype and one microsatellite multilocus genotype for 20 colonies corresponded to those of one P. acuta colony being kept in the tank. One small colony matched both multilocus genotypes. This may have been a chimeric colony resulting from allogenic fusion. These small colonies were not produced sexually, because the only potential parent in the tank was the aforementioned P. acuta colony. Instead, they were more likely derived from asexual planula release or polyp bail-out. Corals as Pocillopora acuta have the capacity to produce clonal offspring rapidly and to adapt readily to local environments. This is the first report of asexual reproduction by planulae or expelled polyps in P. acuta at Okinawa Island.
Highlights
The Nansei Islands, spanning approximately 1,000 km, are located to the north of the coral triangle in the East China Sea and the Pacific Ocean (Fig. 1A)
One mitochondrial open reading frame region (mtORF) haplotype was shared between potential adult colony of P. acuta and the 25 small colonies (GenBank accession number LC390046), and two microsatellite multilocus genotypes were detected (20 colonies of one and four of the other) (Table 1)
We suspected contamination and extracted genomic DNA again; the result was consistent. This may have been a chimeric colony resulting from allogeneic fusion of planula larvae from two different colonies that were not fused when branches of adult colonies were tried to be fused in P. damicornis (Hidaka, 1985; Hidaka et al, 1997)
Summary
The Nansei Islands, spanning approximately 1,000 km, are located to the north of the coral triangle in the East China Sea and the Pacific Ocean (Fig. 1A). This is relatively high latitude (∼24–31◦N) for coral reefs, and includes the northern reef limit in the northern hemisphere (Yamano, 2008). Over 80 coral genera (over 400 species) are abundant in the area (Nishihira & Veron, 1995; The Japanese Coral Reef Society & Ministry of the Environment, 2004). The geographic reef range and coral species diversity appear to be enhanced by the Kuroshio.
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