珊瑚穴居癭蟹的生物學及分子類緣關係之研究

Abstract

本研究以潛水的方式在台灣週圍及各離島諸島沿岸海域共採集9屬9種癭蟹(Cryptochirus coralliodytes; Dacryomaia edmonsoni; Hapalocarcinus marsupialis; Hiroia krempfi; Lithoscaptus paradoxus; Neotroglocarcinus hongkongensis; Pseudocryptochirus viridis; Opecarcinus crescentus; Utinomiella dimorpha)。為了探討癭蟹形態上的演化(癭蟹類群)及癭蟹生態上的多樣性(癭蟹與宿主的關係以及洞穴的建構)，癭蟹之粒線體COI與16S基因片段合併建構之最大簡約關係樹及相鄰連結關係樹顯示9屬9種癭蟹為一單元系群 (monophyletic)，可細分為9個系群。癭蟹分佈之宿主珊瑚種類包含菊珊瑚科(Faviidae)、蕈珊瑚科(Fungiidae)、鹿角珊瑚科(Pocilloporidae)、樹珊瑚科 (Dendrophylliidae)及蓮珊瑚科(Agariciidae)等石珊瑚共計5科18種。各種癭蟹的宿主珊瑚種類及種數不儘相同(介於1-5種)，顯示各種癭蟹對宿主珊瑚的特異性程度不同，但各種癭蟹皆存在特定的珊瑚科別(Family)之宿主特異性。因此同一科之宿主珊瑚的癭蟹可能起源於單一共同祖先。 癭蟹的洞穴形態呈現不規則、圓形、橢圓形、半圓形、雙球面形及新月形等多樣化的形態，且洞穴形態具有高度保守性且與癭蟹類緣關係有關，相關性分析結果顯示，癭蟹背甲寬與其對應之洞穴開口直徑呈現顯著之相關性(p<0.01)，此結果顯示癭蟹具有塑造洞穴形態之能力，因此“洞穴形態”可延伸做為癭蟹的表徵之一。 袋腹珊隱蟹(H. marsupialis)之粒線體合併COI與16S基因片段建構的相鄰連結關係樹及貝葉氏關係樹樹形顯示，採集自5種不同宿主珊瑚之袋腹珊隱蟹之分子遺傳明顯分歧為四個系群(支持度>90%)，各群之遺傳歧異度介於2.2%–7.2%，且遺傳分歧的結果明顯與其棲居的珊瑚的種類相關，而與分佈的地點無關。此結果顯示，袋腹珊隱蟹(H. marsupialis)因宿主特異性及宿主轉換(host-shift)的作用，已導致癭蟹之分子遺傳開始產生分歧。

For this study, nine species of gall crabs belonging to nine genera were collected from scleractinian corals by SCUBA diving from offshore surrounding Taiwan. They were Cryptochirus coralliodytes, Dacryomaia edmonsoni, Hapalocarcinus marsupialis, Hiroia krempfi, Lithoscaptus paradoxus, Neotroglocarcinus hongkongensis, Pseudocryptochirus viridis, Opecarcinus crescentus and Utinomiella dimorpha. In order to understand the evolutions of the morphologic (gall crabs themselves), and ecological diversity (their host relationships, and the construction of their gall/pit) of gall crabs. The phylogenetic tree of Maximum parsimony tree and Neighbor-joining tree (combined partial mt. COI and 16S) illustrated that they belonged to a monophyletic group and subdivided into 9 groups. In addition, host coral species of gall crabs include Faviidae, Fungiidae, Pocilloporidae, Dendrophylliidae and Agariciidae, a total of 5 families and 18 species. A variety of crab host coral species and species vary (ranging from 1-5 species), each gall crab species showed a host-specificity in a Family taxonomic level of their host corals. This might also imply that the members of each gall crab species derived from a common ancestor. A gall polymorphism, incl. irregular, circular, elliptical, semicircular, spheres by two valves, crescent and high degree of conservation of gall shapes was observed in relation to the gall crabs’ phylogeny. In addition, a significant relationship between the crab size (carapace width) and its gall/pit opening size (p < 0.01) demonstrated that the crabs have an ability to shape the gall/pit which suits to their own size. Thus, the galls/pit morphology might be considered as an extension of the crabs’ phenotypes. The Neighbor-joining tree and Bayesian inference tree topology (combined partial mt. COI and 16S) of gall crab H. marsupialis collected from 5 different host corals showed that the significant genetic variation and clearly divided into four clades (support >90%), the genetic diversity of each clade ranged from 2.2% to 7.2%. 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 molecular data had revealed a genetic differentiation as a result of the host shift of H. marsupialis.