笠藤壺於西太平洋至東印度洋之族群生態，遺傳學及親緣地理學研究

Population ecology, genetics and phylogeography of Tetraclita species (Crustacea: Cirripedia) from the West Pacific Ocean to East Indian Ocean

陳璽年(Hsi-Nien Chen)

指導教授 ： 陳國勤

國立臺灣大學/生命科學院/生態學與演化生物學研究所/博士(2016年)

https://doi.org/10.6342/NTU201600142

摘要

笠藤壺屬是印度西太平洋常見的潮間帶藤壺，也是研究潮間帶生物的族群生態，生物多樣性以及生物地理學上常用的模式物種。在西太平洋總共分佈著四種笠藤壺：分別是日本笠藤壺，黑潮笠藤壺，鱗笠藤壺以及新加坡笠藤壺，並各自擁有不同的分佈範圍。本研究主要想要了解笠藤壺從西太平洋到東印度洋之族群生態，生物地理，以及親緣地理學。
族群生態學研究主要聚焦在西太平洋上(日本，台灣及香港)的日本笠藤壺及黑潮笠藤壺，探討族群生態學以及生活史特徵在不同地理區域間的差異，並探討與環境因子的關聯性。研究結果顯示發現，香港的日本笠藤壺族群擁有的同齡群數量(3)顯著小於台灣及日本的族群(> 5)，但是相對於台灣的笠藤壺族群，香港的日本笠藤壺族群具有較高的附著密度以及較快的附著後成長速率，這些差異或許可以歸因於香港較高的海水溫度以及葉綠素a濃度。此外，結果也可以看到笠藤壺釋放幼體、附著、以及入添主要是發生在夏季，因此夏季的洋流模式於笠藤壺於西太平洋至東印度洋的生物地理及親緣地理將會造成巨大的影響。
另一方面，由於黑潮笠藤壺廣泛分佈在西太平洋至東印度洋海域，因此生態生物地理學及歷史生物地理學的研究僅使用黑潮笠藤壺為模式種去進行探討。這個研究總共採集了二十個西太平洋，三個東北印度洋及一個東南印度洋的黑潮笠藤壺族群，並利用粒線體上的COI基因以及細胞核內的微衛星標記進行遺傳多樣性的研究。從粒線體COI基因的結果可以發現：黑潮笠藤壺總共可分為四個特有的遺傳譜系(genetic lineages)，其中一個譜系為黑潮笠藤壺，另外三個譜系中，其中一個譜系雖然在基因上與黑潮笠藤壺有差異，但形態跟黑潮笠藤壺完全相同，因此被鑑定為cf黑潮笠藤壺(OTU 1)；另外兩個譜系(OTU 2及OTU 3)則跟已發表過笠藤壺品種在基因及形態上均不相同，且擁有獨特的背板及楯板形態特徵，因此推論是尚未發表過的笠藤壺品種(T. sp. nov. 1 and 2)。分子變方分析(AMOVA)顯示東北印度洋與太平洋的黑潮笠藤壺族群間在粒線體COI基因上有顯著的基因分化存在。為了更進一步釐清黑潮笠藤壺的親緣地理學，我們從黑潮笠藤壺的轉錄體中發展出了八個微衛星標記。利用這些微衛星標記，STRUCTURE分析結果顯示黑潮笠藤壺包含了四個基因群(genetically distinct group)：其中一個基因群包含了大部分太平洋的族群以及東南印度洋的族群，台灣蘭嶼的族群則形成另外一個基因群，另外兩個基因群則分別包括了兩個菲律賓的族群，以及所有東北印度洋的族群。另一方面，從主座標分析可以看到跟STRUCTURE分析類似的結果，顯示東北印度洋跟太平洋的黑潮笠藤壺族群在基因組成上有一定的差異，且分子變方分析(AMOVA)也證實東北印度洋跟太平洋的黑潮笠藤壺族群在微衛星標記上有顯著的基因分化存在。而且這些基因群之間並沒有太多當代的基因流動(gene flow)，僅有少量的基因流動從西太平洋的族群流向菲律賓的族群。蘭嶼及菲律賓基因群之分佈應跟更新世之冰河避難所有關。
本研究結果顯示笠藤壺之族群生態與生活史可能會受環境因子如海水溫度及食物濃度所影響，並可能進一步影響笠藤壺的地理分佈。除此之外，本研究亦顯示黑潮笠藤壺擁有高度遺傳多樣性，並在基因上有明顯分化的現象，而這些分化可以歸因於更新世的冰河事件或是其他的地質事件，而且當今之海流分佈阻止了黑潮笠藤壺的基因流動，並維持住遺傳群或譜系群間之基因分化。

關鍵字

笠藤壺 ； 族群生態 ； 生活史 ； 親緣地理 ； 族群遺傳

並列摘要

The genus Tetraclita is a common intertidal barnacle in the Indo-West Pacific and a good model for studying population ecology, diversity and biogeography of intertidal species. There are four Tetraclita species in the West Pacific including Tetraclita japonica, Tetraclita kuroshioensis, Tetraclita squamosa and Tetraclita singaporensis and these species have almost allopatric distribution. The aim of the present study was to understand the population ecology, biogeography and phylogeography of Tetraclita barnacles from the West Pacific to East Indian Ocean.
Variations on population ecology and life history pattern of T. japonica and T. kuroshioensis were studied among geographic regions in the West Pacific (Japan, Taiwan and Hong Kong) and correlated with environmental factor. Results showed that T. japonica populations in Hong Kong had the lowest number of cohorts (3) than Japan and Taiwan (> 5). Settlement density and settler growth rate of T. japonica was also higher in Hong Kong compared to Taiwan. These differences probably resulted from higher sea surface temperature and chlorophyll a concentration. Besides, results suggested that larval release, settlement and recruitment of Tetraclita barnacles happen in summer months. It is therefore, the biogeography and phylogeography of Tetraclita species are highly affected by oceanographic processes during the summer months in the West Pacific and East Indian Ocean regions.
T. kuroshioensis was selected as a model to study historical and ecological biogeography because this species had the widest distribution from the West Pacific to East Indian Ocean. A total of 19 populations across the West Pacific, three populations from NE Indian Ocean and one population from SE Indian Ocean were collected. The genetic diversity was examined using mitochondrial COI (cytochrome oxidase subunit I) and nuclear microsatellite markers. Mitochondrial DNA analysis on T. kuroshioensis revealed four distinct genetic lineages. One of the lineages was identified as T. kuroshioensis. Among the other three lineages, one lineage exhibited strong genetic differentiation but had similar morphology to T. kuroshioensis. This lineage was regarded as T. cf. kuroshioensis (OTU 1). In contrast, the other two lineages exhibited genetic variations to the known Tetraclita references and also had distinct morphological features on scutum and tergum. These two lineages were regarded as undescribed Tetraclita species (T. sp. nov. 1 = OTU 3; T. sp. nov. 2 = OTU 2). AMOVA analysis based on mtDNA COI gene showed significant genetic difference between NE Indian Ocean and Pacific Ocean T. kuroshioensis populations. To further elucidate the phylogeographic pattern of T. kuroshioensis, eight microsatellite markers were developed from T. kuroshioensis through transcriptome sequencing. STRUCTURE analysis through microsatellite markers showed that T. kuroshioensis was composed of four genetically distinct groups. One genetically distinct group contained most Pacific Ocean populations and one SE Indian Ocean population (KBA) whereas the OI population formed a genetically distinct group alone. The other genetically distinct groups were composed of two Philippine populations (PGP and BCP) and NE Indian Ocean populations (AII, PKT and PCI), respectively. Alternatively, the PCoA plot showed similar result to STRUCTURE analysis. AMOVA analysis based on microsatellite dataset also revealed significant differentiation between NE Indian and Pacific Ocean populations. The contemporary gene flow among these genetic groups was rare and only found from Pacific Ocean populations to the Philippines populations. The distribution of the OI population and the Philippines populations appears to be related to the presences of glacial refugia during the Pleistocene.
The present results revealed the population ecology and life history pattern of Tetraclita barnacles can be influenced by environmental factors such as sea surface temperature and food availability which might affect geographical distribution as well. The present study also highlighted the hidden genetic diversity of T. kuroshioensis. The strong genetic subdivisions of T. kuroshioensis could be resulted from Pleistocene glaciation or other past geological events. Limited contemporary gene flow from the present day ocean currents also sustained genetic differentiation and prevented mixture among distinct genetic lineages/groups.

並列關鍵字

Tetraclita ； population ecology ； life history ； phylogeography ； population genetics

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