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Reticulate hybridization of Alpinia (Zingiberaceae) in Taiwan and Phylogeography of A. shimadai complex
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。
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.
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