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Phenotypic plasticity of coral-inhabiting barnacles: variations among age, locations on hosts and host species
|Advisor:||陳國勤(Benny Kwok-Kan Chan)|
phenotypic plasticity,coral-inhabiting barnacle,symbiosis,Family Pyrgomatidae,scleractinian coral,
|Publication Year :||2019|
|Abstract:||珊瑚共生藤壺(coral-inhabiting barnacle)為塔藤壺科(Family Pyrgomatidae)的成員，與石珊瑚共生。珊瑚藤壺的基部與外殼，是與珊瑚共生的重要結構。基部能與珊瑚骨骼共同生長使藤壺不會被珊瑚覆蓋而死亡，外殼則可以保護藤壺柔軟的身體。兩者的生長可能會受到不同宿主珊瑚的影響，在外殼與基部出現不同的生長比例。
本研究共鑑定出11種珊瑚藤壺，取自14種宿主珊瑚。藤壺外殼與基部在不同年齡的生長關係，可分為兩類群：離板藤壺屬(Cantellius)與其他類群(包含宋氏高柱藤壺(Cionophorus soongi)、連達氏藤壺(Darwiniella conjugatum)、雄偉貴藤壺(Nobia grandis))。在離板藤壺屬類群於不同年齡基部與外殼生長關係沒有明顯變化，於0-1年與>1年殼長與基部深度支迴歸線斜率相似，外殼與基部皆共同生長。在其他藤壺類群，0-1年殼長與基部深度之迴歸線斜率較>1年之斜率低，顯示在0-1年時主要增長外殼，在>1年則傾向增長基部。而在基部與外殼的形態差別上，所有珊瑚藤壺皆會隨著年齡的增長，而有較長的基部比例。
珊瑚藤壺於不同生長位置、不同形態、不同種類之宿主珊瑚，在基部與外殼生長皆具有表型可塑性。次離板藤壺(Cantellius secundus)生長於分枝形軸孔珊瑚(Acropora sp.)頂端或側邊。生長於珊瑚頂端之藤壺，較傾向生長基部，有較長的基部。真離板藤壺(Cantellius euspinulosum)生長於三種不同形態之微孔珊瑚上(Porites)宿主，生長於團塊形微孔珊瑚的藤壺，較其他兩種宿主珊瑚上，傾向於生長基部。而雄偉貴藤壺(Nobia grandis)中生長於正腔紋珊瑚與棘杯珊瑚上較傾向生長基部；生長於真葉珊瑚則傾向生長外殼。
Coral-inhabiting barnacles are obligatory symbionts of scleractinian corals and fire corals. They belong to the superorder Thoracica, order Sessilia, family Pyrgomatidae. Coral-inhabiting barnacles have modified form of bases and shells. The base of barnacles are embedded with coral skeleton together, and vertical extension of barnacles can prevent the barnacles from being overgrowth by coral. The shell can protect the soft body of barnacle from predators and overgrowth by coral. Due to the differences in growth rates and morphological forms of host corals, the growth pattern of coral barnacles might be affected by the corals.
The purpose of this study was to examine the growth pattern of shell and base of coral barnacles with different ages and among in different location on the same coral host, and among different species of host corals. Coral-inhabiting barnacles were collected from host corals by SCUBA diving and identified using morphological and molecular methods. Shell length and base depth were measured by electronic vernier scale. To examine the variation of base and shell growth among different barnacle age and hosts, relationship of base depth and shell length was analyzed using linear regression. Slopes of the regression line of base depth/ shell length relation was determined. The ratio of base depth and shell length among different age and hosts was compared to determine the morphological change.
We found 11 coral-inhabiting barnacle species in 14 host coral species. The growth pattern of shell and base differed among barnacles with different ages. According to the pattern of base and shell relationships, all the coral barnacles can be divided two groups. One group included the genus Cantellius, the other group included various genus including Cionphorus soongi, Darwiniella conjugatum, Nobia grandis. In Cantellius, barnacle in age 0-1 and >1 year had similar base and shell regression slope, suggesting that the growth pattern of shell and base were not different between ages. In contrast, in the other group of barnacles, their regression slope of the base depth/ shell length regression line varied between different ages. The slope of the base depth/ shell regression line in 0-1 age was lower than in >1 age, suggested the growth rate of shell was faster than the base during the first year after settlement. After first year, shell grew slowly than base. Compared the variation of ratio base/ shell among age groups, all of the coral barnacles have longer proportion of base as barnacles grew older.
Our results suggested that coral barnacles with different ages, living in different coral hosts and different locations on the hosts showed phenotypic plasticity, as indicated by different base and shell growth. Cantellius secundus barnacles lived in coral Acropora sp. and found that barnacles living on the top of coral colonies had deeper base and bigger shell than those from the lateral branch. Cantellius euspinulosum inhabited in three different Porites corals with different growth forms. Compared barnacles living in encrusting or columnar corals, barnacles living in massive coral tend to have higher proportion in base growth rate. Nobia grandis tended to grow deeper base when they inhabiting in corals Coeloseris mayeri and Galaxea sp., while they tended to grow larger shell when lived in coral Euphyllia sp..
Morphology of shell, cirrus, aperture frill varied between the barnacles Nobia grandis among host species. Hence, we used the CO1 gene to analyze the genetic relationship between barnacles from different host corals. Results indicated that N. grandis can be divided in to four major clades in phylogenetics tree. There are over two species of host corals in each clade. The genetic differentiation of N. grandis is less affected by the difference in the host coral species . The variations in growth rate and form among coral hosts might be the possible cause.
The phenotypic plasticity allow coral barnacles to adapt to the diverse coral hosts, thus essential for the survival of coral barnacles with the living coral host together.
|Appears in Collections:||生態學與演化生物學研究所|
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