喀斯特石灰岩洞穴植物之演化研究—苦苣苔科小花苣苔屬之親緣關係

喀斯特地形 (Karst) 具特殊的生境與類似「島嶼」的隔離性質，並具有高比例的特有物種，然而相較於熱帶地區多樣性生成機制詳盡的研究與討論，對喀斯特地區的探討卻相對欠缺。中國南方具有面積廣大且發育完全的喀斯特區域，在此區域中，廣西地區擁有極高的苦苣苔科植物多樣性與特有性，其中小花苣苔屬植物僅侷限於喀斯特岩洞棲地，提供了研究此特殊生態系植物種化機制的良好素材。本研究研究利用細胞核 ITS 與葉綠體 trnL-F 兩段 DNA 序列，來重建 11 種小花苣苔屬 (Chiritopsis)、26 種唇柱苣苔組(Chirita sect. Gibbosaccus) 與其相近13 個屬的苦苣苔科植物間親緣關係，在單一片段與合併處理下的分析結果皆顯示小花苣苔屬、唇柱苣苔組、報春苣苔屬與文采苣苔屬成員組成一個支持度極高的單系群 (稱之中國南方唇柱苣苔支序)，本研究除了再次驗證小花苣苔屬為多起源，更進一步指出該屬在中國南方唇柱苣苔支序中至少 7 個起源。根據本研究之親緣關係，並結合苦苣苔科植物在花形、葉形上具多變性，結合綜合授粉特徵 (pollination syndrome) 的討論，天擇的作用可能導致中國南方唇柱苣台許多的平行演化，故若單以形態外觀來分類廣西地區的苦苣苔科植物，特別是傳統分類學上著重的花部特徵，容易造成不自然的分類處理，反而地理分布與親緣關係較有關聯且具意義，本研究發現由羅城—鹿寨—象州—貴港—邕甯—寧明這六個地理位置的地質分界線與中國南方唇柱苣苔支序植物東、西兩大地理區十分吻合，暗示地質歷史在本支序的分化上可能扮演十分重要的角色。最後，若要了解中國南方唇柱苣苔支序清楚的親緣關係，仍需要進一步的完整採樣，且對於花形、花色與授粉者可能的共演化現象，需要更多野外調查的支持，而廣西地質歷史對種化的關聯性，待其他研究輔助下，才能對此地區高度特有化現象可能因子達到全盤的了解。

關鍵字

石灰岩；特有種；多起源；趨同演徵；地質學；苦苣苔科

並列摘要

Karst landscape harbors a strikingly high level of endemism that is thought to be triggered by its special island-like niches. Although concerns with biodiversity loss have gained much attention, a majority of researches and focuses are on the tropical regions; relative few studies have devoted to investigate mechanisms that fostered the high biodiversity in the Karst ecosystem. The Karst landscape in southern China is a biodiversity hotspot in East Asia. Of the myriads of plant groups that have contributed to the high botanical diversity in the region, the family Gesneriaceae is amongst the most conspicuous and representative taxa. This thesis studies the phylogenetics of Chiritopsisi, a small genus confined to the limestone caves of southern China, to understand the mechanisms that have generated the high endemism in the Karst landscape. Phylognetic relationships of 11 species of Chiritopsis, 24 species of Chirita sect. Gibbosaccus, and 13 related genera were reconstructed based on nuclear ITS and chloroplast trnL-F DNA sequences using criteria of maxim parsimony and Bayesian inferences. A highly supported clade (designated as South China Chirita clade herein) including all species of Chiritopsis and Chirita sect. Gibbosaccus, Primulina tabacum, and Wentsaiboea renifolia, was unveiled. Conforming to previously analysis, Chiritopsis is polyphyletic and our results further indicate at least seven independent origins of this genus. Based on the phylogenetic relationships, it is evident that the vegetative and reproductive morphological traits and pollination syndrome traditionally used for taxon delimitation in Gesneriaceae are highly hompolasious in Chiritopsis and taxonomy of this clade has to be recircumscribed. On the contrary, species clutered together in a clade are mostly distributed in geographic proximity. A majory demarcation separating the South China Chirita clade into eastern and western subclades corresponds well to a geograpohic divide lining from Luocheng, Lujhai, Siangjhou, Gueigang, Jungning, to Ningming, a boundary that have resulted from a series of geological events in the region. This finding suggest that, historical events, rather than ecological factors, should have been crucial in generating the high biodiversity in the Karst ecosystem in Guangxi, China.

並列關鍵字

limestone ； endemic ； polyphyletic ； homoplasy ； geology ； Gesneriaceae

參考文獻

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喀斯特石灰岩洞穴植物之演化研究—苦苣苔科小花苣苔屬之親緣關係

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