梅山口鐵線蕨(Adiantum meishanianum)是目前只發現在高雄市梅山村的臺灣特有種蕨類,由於其分佈範圍侷限,加上前人研究發現其為三倍體並產生不孕的孢子,因此被認為是一雜交種,根據前人形態觀察及初步分子資料顯示可能的親本應為鞭葉鐵線蕨(A. caudatum)、馬來鐵線蕨(A. malesianum)及半月形鐵線蕨(A. philippense)。本研究針對上述物種在全臺灣採樣不同族群,使用倍體性、生殖模式及分子親緣分析梅山口鐵線蕨之可能雜交起源。倍體性分析顯示鞭葉鐵線蕨有二、三倍體族群,馬來鐵線蕨均為四倍體、半月形鐵線蕨則可發現二、三倍體族群,唯二倍體族群目前只發現在梅山口生育地附近以及高雄扇平。分子親緣分析使用核基因-隱花色素基因2 (Cryptochrome gene2 , CRY2)的第一內插子片段與兩段葉綠體基因標記:rps16-matK基因間隔區(IGS)及matK基因以檢測其雜交親本。結果顯示,梅山口鐵線蕨的葉綠體序列與馬來鐵線蕨相同,在核基因部分則是分別與馬來鐵線蕨及半月形鐵線蕨相同。結合倍體數、生殖模式及分子親緣分析的結果可知四倍體馬來鐵線蕨為梅山口鐵線蕨之母本,而半月形鐵線蕨中的二倍體為其父本。此結果同時也暗示了梅山口鐵線蕨之所以稀有,也許是由於二倍體的半月形鐵線蕨族群於臺灣侷限分布的緣故。
Adiantum meishanianum is an endemic species distributed only in Meishan village, Kaohsiung, Taiwan. Adiantum meishanianum has been regarded as a hybrid origin. Previous studies suggest that A. caudatum, A.malesianum and A. philippense are its putative parents. Its sporangium contains only abortive spores implying its triploidy. The aim of the study is therefore to determine the hybrid origin of A. meishanianum by examining cytological status, reproductive strategy and reconstructed molecular phylogeny among these species. In A. caudautum we identified diploid and triploid populations around Taiwan. In A. malesianum we discovered only tetraploid populations. Both diploid and triploid populations were found in A. philippense, whereas the diploid population can only be discovered near the locality of A. meishnainaum and ShanPing, Kaohsiung. Based on the phylogeny reconstructed through one nuclear marker - Cryptochrome gene 2 intron1 (CRY2 intron1) and two chloroplast markers - rps16-matK intergenic spacer (IGS) and matK gene, I found that the chloroplast sequences of A. meishanianum were identical to those of A. malesianum. In addition, the two nuclear CRY2 intron1 alleles of A. meishanianum were resemble to A. philippense and A. malesianum, respectively. The results indicate that the maternal species is the tetraploid A. malesianum and the paternal species is the diploid A. philippense. The rarity of A. meishanianum may be resulted from the limited distribution of the diploid populations of A. philippense thus the hybridization events did not occur regularly.
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