サンゴ礁無脊椎動物における集団遺伝解析による種分化および幼生分散の推定

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  • 安田 仁奈
    宮崎大学テニュアトラック推進機構
  • 灘岡 和夫
    東京工業大学情報理工学研究科情報環境学専攻
  • 長井 敏
    水産総合研究センター中央水産研究所　水産遺伝子解析センター

書誌事項

タイトル別名
  • Speciation and larval dispersal of coral reef invertebrates using population genetic analysis
  • サンゴショウムセキツイ ドウブツ ニ オケル シュウダン イデン カイセキ ニ ヨル タネ ブンカ オヨビ ヨウセイ ブンサン ノ スイテイ

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<p>Coral reefs have amongst richest biodiversity of all the shallow marine ecosystems. However, coral reefs are severely threatened by global warming as well as local anthropogenic stresses world-wide. Establishing proper Marine Protected Areas (MPAs) is considered as the most feasible and effective approach for the conservation of marine ecosystems. Although adults are sessile, many coral reef invertebrate species have a pelagic larval stage in their early life history; therefore the estimation of larval dispersal is essential for planning MPAs. Because planktonic larvae are very small and morphologically indistinguishable, direct tracking of larval dispersal in the vast ocean is almost impossible. In this paper, we shortly review genetic methods for estimation of larval dispersal and species delimitation, exemplifying three starfish taxa with relatively long pelagic larval duration (PLD) of 2–7 weeks as well as blue coral with a relatively short PLD (a few hours–2 weeks). Population genetic analysis of crown-of-thorns starfish, Acanthaster planci, across the Indo-Pacific Ocean using highly polymorphic microsatellite loci revealed genetic homogeneity along strong western boundary current such as the Kuroshio (over 2,600 km from the Philippines to Japan) and the Eastern Australian Current (along the Great Barrier Reef) which partly supports the secondary outbreak hypothesis via larval dispersal. Indeed, successive population outbreaks of A. planci have been chronically reported especially a few years after the approach of the Kuroshio to the Ryukyu Islands. On the other hand, significant genetic differentiation was found among remote Pacific Islands, rejecting the secondary outbreak hypothesis for these Pacific islands. Further intensive sampling together with the genotyping of multiple loci (nuclear microsatellite and mitochondrial DNA) revealed that strong gene flow occurs via larval dispersal at sites up to 200 km apart along the Society Islands in French Polynesia, implying possible secondary outbreak without strong ocean currents. Mitochondrial analysis of crown-of-thorns starfish, as well as other coral reef starfish species such as pincushion starfish and blue starfish, showed genetic discontinuity between the Indian and Pacific Oceans, implying the possible effect of sea level fluctuations during the Pleistocene. Despite distinct differences in morphology and ecology between the sibling Linckia species (Linckia laevigata and Linckia multifora), the two species shared the same haplotypes of mitochondrial DNA and could not be distinguished species by mtDNA sequences. However, population genetic analysis of the two species using microsatellite loci across Indo and Pacific Ocean indicate that morphologically different populations are weakly differentiated (Yasuda et al. in prep). While mitochondrial DNA is useful for species delimitation due to its higher mutation and sorting rate than nuclear DNA, this result highlighted the fact that caution is warranted when we are to delimit recently speciated taxa and a population-based approach covering the species-range is robust enough to examine speciation history. Population genetic analysis of blue coral, Heliopora coerulea, which has a relatively short PLD, indicated that there are at least two evolutionary different clades along the Kuroshio. Each of the two cryptic clades (possible cryptic species) distributed along the Kuroshio and tend to appear in different environments, implying some environmental and/or biological factors are associated with their distributions. Significant isolation by distance patterns were found in each genetic clade of H. coerulea, suggesting the split of the two genetic clades occurred a relatively long time ago and that each genetic clade thereafter spread out into their preferred habitats along the Kuroshio.</p><p>(View PDF for the rest of the abstract.)</p>

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