| Summary: | 博士 === 國立臺灣大學 === 海洋研究所 === 99 === 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.
|
|---|
