台灣冷杉族群遺傳變異之研究

Abstract

台灣冷杉為台灣特有之冰河孑遺針葉樹種，其分佈範圍主要介於海拔2400∼3800 m，北緯約23°N ∼ 24.8°N，屬於本島之亞高山地帶主要林相。北自南湖大山，南至卑南主山，大致呈連續性分佈。海拔分布範圍邊界與玉山箭竹、玉山圓柏、鐵杉林形成動態推移。本身具有週期性的繁衍特質，並且在此生育地，面臨不等間隔的火燒干擾。本研究利用ISSR指紋分析方法，探討台灣冷杉族群之遺傳變異。結果顯示，其多數鄰近山系分布的族群，彼此間遺傳關係較為相近，由歸群分析與主座標分析結果顯示，以南湖大山與審馬陣山、關山與向陽山及合歡山、雪山、干卓萬山與奇萊山三個群組之遺傳及地理關係最為明顯，僅大霸尖山與其他族群的遺傳關係不具地理分布相關性。且其族群間已有明顯的遺傳分化現象（Gst為0.3237）；並且有明顯的族群間基因流（Nm為1.0445）。其族群分化可能肇因於山岳地形與距離對於族群的區隔，而基因流的發生應為藉風力運送的花粉與種子所驅動之，但對於族群分化與基因流同時造成不等程度的貢獻。至於基因流的方向與遺傳分化少數不具地理相關性的結果雖無實質證據或結果，但可能為受到季風與因地形所造成的對流所影響。族群遺傳分析結果整體而言顯示具有相當高的遺傳變異，而其變異主要集中於族群內。至於遺傳歧異度較高的族群主要集中中央山脈北端審馬陣山至中段干卓萬山之間，以審馬陣山及合歡山族群遺傳歧異度最高。整體歧異度指數（H）為0.3641。利用4CL基因序列之種系發生分析結果，對於探討族群間種系發生關係而言，無法完全反映台灣冷杉族群的親源遠近，且對於兩代之間因序列變異所造成的演化樹分支亦無法呈現具體關係。以胚乳樣本進行族群的演化關係探討上，其演化樹無法呈現良好的解析結果。至於以4CL與NAD5基因序列探討台灣冷杉與GenBank松科其他物種間的關係，大致吻合前人的分析結果，對於屬間的種系發生關係有清楚的解析，但兩序列分別以貝貽推論分析（BI）或最大儉約分析（MP）所得演化樹，對於冷杉屬內演化關係無法清楚的釐清。而本研究所採用的BI與MP分析方法，對於不同的分類層級的分析結果均指出，BI分析對於演化樹末梢分支的解析能力較強，且對於分支節點給予較高的支持度，對於運用屬以下的演化關係分析應用應該是適合的分析方法。然而，在NAD5的分析結果中，卻顯示出在演化樹根部的弱解析結果。族群遺傳分析結果建議台灣冷杉族群保育生物學的Hotspot應為審馬陣山及合歡山等族群，對於維護這些族群生育地的完整性，以及與其他族群間的連續性，應是主要重點。而在全球環境變遷議題下，氣候的異常可能對於亞高山帶的台灣冷杉形成生存壓力，有必要建立長期族群遺傳資料，提供保育策略的參考。而本研究中除族群遺傳分析所得相關結果，可作為瞭解其遺傳結構的參數外，因生物演化歷史才是造就生物歧異度的最終因素。因此，在演化樹上具較長演化歷史的族群其相對具有演化上的重要性，如畢祿山、雪山、玉山、向陽山等族群，在物種保育策略中同時可以列為重點考量。

Taiwan Fir is a glacial relic conifer species endemic to Taiwan. It is distributed from 2400 m to 3800 m in altitude and from 230 N to 24.80 N in latitude. Its distribution is more or less continuous from Nanhudashan in the north to Beinanchushan in the south. Its neighboring species usually include species of Yushania, Juniperus, and Tsuga. The reproduction of the species is generally in cycles and its habitats experience forest fire periodically. The genetic variation of the species was investigated in the present study using ISSR fingerprinting method. The result indicated that most of the neighboring mountain systems have closer genetic relationships. Cluster analysis and principal coordinates analysis revealed close relationships between neighboring Nanhudashan and Shiunmagiunshan; Guanshan and Shianyanshan; and Hohuanshan, Shieshan, Ganzuowanshan and Chilaishan. The genetic differentiation among populations is significant (Gst = 0.3237) and there is gene flow among populations (Nm = 1.0445). The population differentiation may be resulted from specific mountain landscape and isolation by distance. The gene flow is resulted from wind transportation of pollens and seeds. The population genetic analysis revealed that the species has high genetic variation, with the variation source mainly within populations. The northern and central portions of the Central Mountain Range from Shiunmagiunshan to Ganzuowanshan have high genetic diversity, with Shiunmagiunshan and Hohuanshan the highest diversity. The total diversity index (H) of the species was 0.3641. The result of phylogenetic study using 4CL sequence data was unable to reveal the relationship among populations. The 4CL sequences of endosperm samples were also unable to resolve the relationship among populations. The result using 4CL and NAD5 sequences of Taiwan Fir and other species of Pinaceae from GenBank indicated that the relationship among species generally is congruent with the result of a previous study. The study resolved the relationship among genera. However, both Bayesian Inference and Maximum parsimony analyses failed to clarify the relationship among species of the genus Abies. The comparison between methods of BI and MP indicated that BI has good resolution near terminal of evolution tree and generally has higher support for each clade. However, in the NAD5 analysis using BI it has weak resolution near the root of the tree. Population genetic analysis indicated that the Hotspot of the conservation biology of Taiwan Fir is located around Shiunmagiunshan and Hohuanshan. The conservation of these populations is critically important. The global climatic change may be a stress for Taiwan Fir and it is suggested that long term population genetic data should be established for conservation consideration. Some parameters of the genetic structure of Taiwan Fir have been provided in the present study. The most important factor in determining genetic diversity is the evolution history of the species concerned. Populations that experienced longer evolutionary history generally have greater genetic diversity and are more important in conservation. Therefore, populations of Beelushan, Shieshan, Yushan, and Shianyanshan should also be emphasized in conservation policy.