台灣產月桃屬植物天然雜交及島田氏月桃複合群親緣地理之研究

Abstract

台灣產月桃屬植物之系統分類處理歷來未能獲得一致認同的結果，推測頻繁的天然雜交及島田氏月桃複合群內特徵多變異是主要的難點，故本論文針對此二方向進行探討。 台灣月桃屬網狀雜交關係假說的提出根據形態特徵、花粉孕性偏低及地理分布等特性。本研究透過分子方法證實此假說；除了雜交個體及其親本種的鑑別，單向或雙向的雜交配對模式也獲得確認。共鑑別出9種來自不同物種配對組合的雜交，佔所有15種可能組合的60%。透過比較這些雜交配對特性之異同點，推論生態地理屏障(ecogeographic barriers)、傳粉者精確度(pollinator fidelity)以及雜交不親和(cross-incompatibility)是月桃屬植物關鍵的生殖屏障；依序在其生活史中發生作用以達到物種維持。然而，在不同配對物種間，每一生殖屏障的貢獻度有所差異。 島田氏月桃複合群為台灣特有，其分化的歷程深受台灣地質歷史之影響。本研究全島採樣226個體，結合兩段葉綠體非轉錄區序列進行分析，結果顯示中央山脈兩側的遺傳組成有顯著的差異；檢視形態特徵「小苞片有無」獲得與地理親緣相符的歸群結果，此複合群應區分為普萊氏月桃及島田氏月桃兩支系。普萊氏月桃不論在單型及核苷酸的變異度上均高於島田氏月桃，代表其較長的族群歷史以及較複雜的變動歷程。這一群植物的共同祖先約在更新世抵達台灣，中央山脈的阻隔與多次的冰河進退可能對這群亞熱帶森林性植物的種化、遷移及生存扮演關鍵的角色；台灣東南端山區及阿里山山脈分別被推論為普萊氏月桃及島田氏月桃的潛在避難所。 綜合以上結果，台灣產月桃屬之關係已得釐清，包含6個具有明確種別特徵的種類。由於不同配對種間生殖屏障的破壞，產生各式樣的雜交後代，造成野外族群形態及遺傳組成上的許多變異。Systematics of Alpinia in Taiwan has been progressively studied, but without consense result. Interspecific natural hybridizations and the polymorphic characters in A. shimadai species complex were presumely the major problems, and are the two principal targets in this dissertation. Reticulate hybridization in Taiwanese Alpinia has been suggested based on morphological, pollen fertility, and geographic features. In the study, we discerned the identities of hybrids and their parental species. Both unidirectional and reciprocal hybridizations were observed. In total, nine of fifteen possible species pairings (60%) have been recognized. Based on comparative studies from different categories of hybrid structure, ecogeographic barriers, pollinator fidelity, and cross-incompatibility were inferred as three sequential critical reproductive barriers for species maintenance. However, the contribution of each barrier varied among species pairings. As an endemic taxon, differentiation of Alpinia shimadai complex was thought to concertedly coincide with the geological history of Taiwan. Chloroplast sequences of two non-coding regions from 226 samples were analyzed. A significant structure with haplotype composition between west and east side of the Central Mountain Ridge (CMR) was identified, a result consistent with the differentiation at morphological trait of bracteole. Accordingly, two lineages of A. pricei and A. shimadai, within A. shimadai complex were evidently distinguished. Higher genetic diversity detected in A. pricei suggested a longer demographic history and/or more complicated evolution process. The colonization of the recent common ancestor in Taiwan was estimated during Pleistocene. Standing of the CMR and iterative advance and retreat of glacial cycles facilitated speciation, migration, and survival of these plants resided in subtropical forests. Mountainous regions in southeastern Taiwan and the Alishan Mountain Ridge were inferred as potential refugia for A. pricei and A. shimadai, respectively. Combining results from the above, systematics of Taiwanese Alpinia has been well framed. Six indigenous species with defined diagnostic characters were identified. Moreover, the breakdown of reproductive barriers among different species pairings contributed the diverse hybridization and thus resulted in great morphological and genetic variations found in field.