Sexually derived larvae, intracolonial genotypic variations, and heterozygosity excess of a brooded coral (Pocillopora damicornis) in Taiwan revealed by microsatellite markers

• Main Authors: Shang-Ru Yeoh, 楊尚儒
• Other Authors: Chang-Feng Dai
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/42226117620908086193

碩士 === 國立臺灣大學 === 海洋研究所 === 95 === The thesis described a research conducted on the fine-scale clonal genetic structure of a brooded coral, Pocillopora damicornis, which is widely distributed throughout the world’s coral reefs. Seven simple tandem repeat (STR) loci, or microsatellites, were utilized to characterize coral colonies sampled in the HoBihoo area, Nanwan Bay, southern Taiwan; among them, four microsatellite loci (PD1, PD2, PD3, and PD5) were independently developed by us in this study. In order to elucidate the potential sperm dispersal distance of this coral species, two populations (HB1 and HB2) were sampled exhaustively, i.e. all observed coral colonies were sampled within a demarcated area that was centered by a mother colony (n=41x2). A third population (HBc) was sampled randomly for index comparisons only (n=25) due to its distinct geographic environment and lower colony density. Besides, we also randomly collected and genotyped 100 larvae from each mother colony during planulations. A high proportion of the 200 larvae genotyped multilocusly were found to be clonal (82.5%), indicating asexual reproduction was the main reproductive strategy for P. damicornis within this area; among these larvae, only 12 genotypically distinct ones (total n=35) could be successfully traced down to their father colony. At the colony-level, a high proportion of the clonal genotypes was also found (74.8%); what is more, intracolonial genotypic variations from the identified clonal genotypes were observed as well. In order to objectively define the line drawn between genotypic variations caused by sexual recombinations and somatic mutations (the assumptive cause of intracolonial genotypic variations), 10 clonal lineages were tentatively grouped (C1-C10) with a threshold value inferred from the genotypic distance matrix. Then the probability that a given clonal lineage thus defined was only the coincidental product by chance alone (Psex) was calculated from the observed allele frequencies for each clonal lineage. At last, we compared these probabilities with the statistical boundaries set at the 5% level (critical-Psex) obtained from computer simulations. In this way, we could therefore verify these clonal lineages with a statistical viewpoint; C1 dominated the area of study by 53% in number and was the biggest clonal lineage. Last but not least, heterozygosity excess, a phenomenon rarely seen in sessile marine invertebrates, was observed at both the colony- and larva-level. Possible interpretations included widespread asexual reproductions, selection for heterozygotes (heterosis), and reproductive self-incompatibility.