台灣近海石珊瑚寄生性珊虱(橈足類)之系統分類學與生態學

Abstract

橈足類是一群種類數量眾多的甲殼類動物，其中寄生於造礁珊瑚群體上的種類超過365種，廣泛分布於印度－太平洋珊瑚礁區，但是在西太平洋北部則甚少研究，而且牠們與珊瑚的關係也缺乏了解。本論文之目標為調查台灣海域產石珊瑚群體上的寄生性橈足類之物種多樣性，探討牠們的親緣關係及其與宿主珊瑚在演化上的關係，並且探究橈足類感染與宿主珊瑚體內共生藻的關係。 在寄生性橈足類之物種多樣性方面，本研究在採集自台灣各海域的888株109種石珊瑚小群體上，共發現36種寄生性橈足類，包括1新屬新種 (Hastatus faviae)、4新種(Wedanus formosanus, Orstomella yaliuensis, Xarifia insolita, X. longa)、8種可能新種及23種新記錄種。 在親緣關係方面，本研究對81種珊虱科橈足類進行支序分析(Cladistic analysis)，以Sabelliphilidae為外群，選用了40個外部形態特徵，利用儉約性與最大相容性原則，建構牠們之間的親緣關係，並以TreeMap探討其與石珊瑚之間的演化關係。結果顯示珊虱科為一單系群，其中細毛虱屬(Zazaranus)可能為較早衍生出的種類，牠們可能起源於印度洋，其後逐漸往太平洋分佈，並且與石珊瑚有某種程度的共演化關係。 在寄生性橈足類與珊瑚的關係方面，為了瞭解寄生性橈足類是否攝食共生藻，本研究利用組織學切片、掃瞄式及穿透式電子顯微鏡檢視珊虱的腸道內含物，結果發現牠們體內皆具有共生藻(Symbiodinium sp.)；螢光顯微鏡觀察結果發現這些共生藻能在珊虱體內存活三週以上，且仍保有行光合作用的能力；其次，培養實驗的結果顯示，共生藻可能將其光合作用產物提供給珊虱利用，因而對珊虱的存活率有益；此種共生關係可能代表橈足類與共生藻建立共生關係的初始階段，而珊虱體內保有共生藻的現象有助於共生藻在珊瑚礁上的散布。 在橈足類感染與珊瑚共生藻密度的關係方面，本研究於2007年7月至2008年11月間，調查台灣南部南灣海域細枝鹿角珊瑚(Pocillopora damicornis)群體上橈足類的感染情況與共生藻密度的關係，結果顯示在2007年的夏季，珊瑚感染珊虱的盛行率、平均密度、平均豐度及平均強度皆較高，而且白化珊瑚群體的珊虱平均密度高於健康珊瑚及嚴重白化珊瑚群體。此結果顯示橈足類的感染情況與珊瑚的健康狀況及共生藻密度有密切關係，而珊虱感染密度在白化珊瑚較高的現象可能會使白化珊瑚更惡化而加速其死亡。 本研究結果顯示，珊瑚寄生性橈足類物種多樣性很高，並且與石珊瑚在演化及生態上有密切關係。本論文增進我們對珊瑚寄生性橈足類系統分類學及生態學的瞭解，並且提供做為珊瑚礁保育的基礎資料。

Copepods are one group of diverse and abundant crustaceans associated with scleractinian corals in Indo-Pacific Ocean. To date, more than 365 species of copepods associated with corals have been discovered, however, very little is known about the species diversity of parasitic copepods in corals from North Pacific and their possible effects on scleractinian corals. The objectives of this study were (1) to discover the species diversity of these parasitic copepods in the surrounding seas of Taiwan, (2) to reveal their phylogeny and evolutionary relationships with coral hosts, (3) to uncover the relationships between parasitic copepods and zooxanthellae. A total of 888 colonies in 109 species of scleractinian corals were examined for collecting parasitic copepods at various localities in Taiwan from 2005 to 2010. Totally, 36 species of copepods including 1 new genus and species (Hastatus faviae), 4 new species (Wedanus formosanus, Orstomella yaliuensis, Xarifia insolita, and X. longa), 8 possible new species, and 23 new recorded species were discovered. Cladistic analyses were carried out using parsimony and compatibility criteria to restructure the phylogeny of Xarifiidae. The Sabelliphilidae was selected as an outgroup in the analyses, and a total of 40 morphological characters were ordered from 81 species of Xarifiidae. The TreeMap was used to examine the possible co-evolutionary association by comparing the phylogenies of corals and xarifiid copepods. The results suggested that the Xarifiidae was monophyletic and the genus, Zazaranus, was the first lineage diverged from the xarifiid clade. They might originate from Indian Ocean and gradually dispersed to Pacific Ocean and develop a co-evolutionary relationship with their coral hosts. In order to know whether parasitic copepods feed on zooxanthellae cells from their host corals, the xarifiid copepods were examined by histological section and electron microscopic observations (SEM and TEM). The results showed that their guts contained many zooxanthellae cells (Symbiodinium sp.). In the fluorescent microscopic observations, these algal cells possibly remained viable and photosynthetically active for at least 3 wk. The results of cultivation experiment suggested that the zooxanthellae may be beneficial to the survival of xarifiid copepods under light condition, possibly through conducting photosynthesis and releasing photosynthetic products to them. The relationships between copepods and zooxanthellae might be referred to a primitive form of invertebrates-zooxanthellae symbiosis. The viable zooxanthellae in the guts of xarifiid copepods may provide a source for dispersal over coral reefs. In the study of relationships between copepods and zooxanthellae density, a coral species, Pocillopora damicornis, was examined in Nanwan Bay, southern Taiwan from July 2007 to November 2008. The results showed that prevalence, mean density, mean abundance and mean intensity of xarifiid copepods were higher in the summer of 2007. The mean density of xarifiid copepods was higher in the bleaching corals, but it was much lower in healthy corals and heavily bleached corals. These results suggested that the occurrence of xarifiid copepods might relate to healthy condition of coral hosts and their zooxanthellae density. The high infection by xarifiid copepods in bleaching corals might further jeopardize the survival of corals by reducing their zooxanthellae density and inducing more physiological stress.。 The results of this dissertation showed that the parasitic copepods have high species diversity and close relationships of evolution and ecology with host corals. The contributions of this dissertation provided basic information concerned in systematics and ecology of parasitic copepods from corals in Taiwan. These results may also have some valuable implications for the conservation of coral reefs.