玉山金絲桃之族群遺傳研究

Abstract

玉山金絲桃（Hypericum nagasawae Hayata）與能高金絲桃（H. nokoense Ohwi）皆為台灣特有種，由於二者形態相似，常造成鑑定上之混淆。本研究以accD – psaI、trnE – trnT、rpl16 intron、trnV – trnM（包含trnV intron）4個葉綠體DNA非轉錄區段進行分析，結果支持Robson (1996) 之處理，將此類群區分為兩種，其中玉山金絲桃廣泛分佈於海拔2,300 m 以上山區，能高金絲桃侷限分佈在花蓮秀林鄉之石灰岩地質地區。

另針對玉山金絲桃共採集10個族群150個樣本，以葉綠體DNA accD – psaI 及 trnE – trnT兩基因間片段探討族群遺傳結構，結果共得到10種單套型，其中4個主要單套型佔了所有樣本的90%，各侷限分佈於特定區域，族群間具有高度分化且基因交流有限（mean FST = 0.744, Nm = 0.09）。北大武山之單套型皆為該族群特有，且與其它單套型差距最遠，顯示受到長期地理隔離之影響，若不計北大武族群，則各族群間之遺傳距離與地理距離呈中度正相關。根據巢狀支序分析（NCA）推論過去在間冰期時曾發生育地碎裂化，使各區域僅保留少數甚至一種單套型，隨後因冰期氣溫下降，族群分佈至較低海拔而使各族群間有所接觸，發生有限之基因交流。

綜合與前人研究之高山類群比較，台灣高山草本植物之遺傳多樣性中心在中央山脈北段，且許多類群皆有雪山地區與南湖大山特有之單套型，其分佈模式可能受到過去冰期及冰河作用而產生遺傳漂變。然而綜合中性假說測試與BEAST軟體分析其族群變動顯示，最近的一次冰期對於玉山金絲桃之族群大小未造成明顯影響。Hypericum nagasawae Hayata and H. nokoense Ohwi are both endemic species in Taiwan. It is difficult to determine these two species since the closely morphological similarity between them. In this study, 4 chloroplast DNA non-coding regions, accD – psaI intergenic spacer, trnE – trnT IGS, rpl16 intron, and trnV – trnM (trnV intron included) IGS, were used to analyze their relationship. The results of molecular analysis are consistent with the taxonomic treatment of Robson (1996). Geographically, H. nagasawae is widely distributed in mountainous regions above 2,300 m in Taiwan, while H. nokoense is restrictively distributed in limestone regions in Shiu-Lin Township, Hualien.

In order to uncover the population genetic structure of H. nagasawae, a total of 150 samples were collected from 10 populations, and two chloroplast DNA intergenic spacers, accD – psaI and trnE – trnT, were analyzed. 10 haplotypes were detected with 4 main haplotypes limitedly distributed in specific regions. Genetic differentiation among populations was generally high (mean FST = 0.744, Nm = 0.09).

Both haplotypes in Mt Peitawu are endemic with the farthest genetic distance from other haplotypes. It suggested that the populations between Mt Peitawu and other regions have a long-term geographical isolation. The genetical distance and geographical distance (Isolation by distance test) have a moderate positive correlation when the population of Mt Peitawu was excluded. According to the result of Nested Clade Analysis, past fragmentation followed by range expansion had occurred.

By integrating the present result and previous studies for other alpine plants, Northern Central Ridge was the genetic diversity center of alpine herbs of Taiwan. Glaciation might have played an important role contributed to the distribution pattern of haplotypes. According to neutral theory test (Tajima’s D, Fu& Li’s test) and BEAST software, however, last Glacial Age did not significantly influence population size.