Genetic Diversification of the Gall Crab, Hapalocarcinus marsupialis (Crustacea: Decapoda: Cryptochiridae), Related to Their Host Corals (Scleractinia: Pocilloporidae)

To determine the level of genetic divergence among gall crab (Hapalocarcinus marsupialis) specimens inhabiting different host coral species and their host specificity, 39 individual animals on five species of host coral were sampled from four localities offshore around Taiwan. The mitochondrial DNA (partial COI and 16S genes) of all specimens was sequenced. Phylogenetic analysis revealed significant genetic variation and four distinct clades, with H. marsupialis individuals in each clade dwelling on specific host corals species. Comparative genetic divergence values with those of other taxonomic groups of decapods or those of other gall crab, genetic divergence between H. marsupialis clade Pve and each of the other clades pair, whether combined COI-16S or COI alone, are within those ranges. Other than the Pve clade, in which H. marsupialis shared two host coral species, the remaining Sh, Sp, and Pd clades, consisted of H. marsupialis samples derived entirely from single host coral species, with no overlap between the clades. The phylogeny tree reveals that the genetic divergence of H. marsupialis is strongly related to differences among host corals, rather than the geographical distribution of H. marsupialis. The observed divergence, strong node support, and well-resolved structure of the phylogenetic topology, suggest that the processes of this genetic diversification may lead to an emergence of cryptic species of the genus Hapalocarcinus ultimately. However, this study given an example of what appears to be a widespread phenomenon of species genetically diversifying in response to the change of hosts, and the genetic diversification might ultimately result in speciation.

關鍵字

Cryptic species ； Host specificity ； Sympatric ； Gall crab ； Host shift

並列摘要

珊瑚共生蟹－癭蟹（gall crab，Hapalocarcinus marsupialis），其分類地位屬於節肢動物門（Phylum Arthropoda）、甲殼綱（Crustacea）、十足目（Decapoda）之隱螯蟹科（Cryptochiridae）。各種癭蟹以形成蟲癭、管道或洞穴狀的的方式寄生在特定種類的石珊瑚活體上。為了研究棲息於不同珊瑚物種宿主的癭蟹所產生的遺傳分歧，本研究從台灣週圍四個珊瑚礁分佈的地區採集39個含有癭蟹個體的珊瑚碎片，這些宿主珊瑚碎片包含三個屬共五種，分別為Pocillopora verrucosa（Pv），Pocillopora eydouxi（Pe），Pocillopora damicornis（Pd），Stylophora pistillata（Sp），and Seratopora hystrix（Sh），並將所有的癭蟹個體進行粒線體DNA片段（mt.COI和16S）進行定序分析，並繪製分子類緣關係樹。結果顯示，棲居在不同種類的宿主珊瑚的同種癭蟹，依據宿主珊瑚種類的不同，可明顯區分為四個群體。癭蟹雖然在外部型態上仍未發現有明顯的差異，但在其分子階層上已有顯著的分歧現象，且此分歧明顯與其棲居的珊瑚的種類相關，而與分布的地點無關。因此本研究結論，癭蟹因定居在不同種類的宿主珊瑚上造成天擇壓力已經在分子階層產生分歧的現象，進而可能導致種化的發生。

並列關鍵字

隱存種；宿主專一性；同域；癭蟹；宿主移轉

國際替代計量

Genetic Diversification of the Gall Crab, Hapalocarcinus marsupialis (Crustacea: Decapoda: Cryptochiridae), Related to Their Host Corals (Scleractinia: Pocilloporidae)

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