青剛櫟葉綠體DNA變異的空間分佈模式

Abstract

本研究以葉綠體DNA trnT-trnL、trnV-trnM及petG-trnP三個基因間片段（intergenic spacer）含trnV intron的序列分析青剛櫟Cyclobalanopsis glauca的族群遺傳結構及親緣地理關係。青剛櫟樣本共採自32個族群，台灣25，沖繩島中部及南部各1，廣東、香港及日本京都、九州、鹿兒島各1，共分析了140株。定序的結果總長度為1961-1983 bp，包含15個多型性位點（polymorphic sites），其中12個來自點突變（point mutation），3個來自插入（insertion），共組成13個單套型（haplotype），其中兩型（A和B）普遍存在東亞地區，故可推知在上次冰河期時，台灣的青剛櫟族群在此三段cpDNA基因間片段中，至少容納了兩個祖先型。有趣的是，所有獨特的變異都只出現在台灣島內。台灣島內整體的遺傳分化指數相當高（Gst＝0.612）。中央山脈是青剛櫟在台灣島內無法做東西向基因交流的重要屏障，在中央山脈的西部族群中，分散在北、中、南的三個族群（陽明山、霧社和浸水營）有最高的單套型歧異度，但族群內的單套型都是姊妹型（sister haplotype），也就是都來自同一個祖先型，因此可能都是上次冰河期後族群拓殖到時才衍生出來的，這個推論和西部沒有空間自相關的分析結果一致；中央山脈東側，兩個關係遙遠的血系（lineage）（D和F）呈現顯著的空間遺傳結構，NST—GST的估計值為負值（-0.090），表示在中央山脈東側的小尺度空間內族群存在親緣地理結構，結合已發表的孢粉學紀錄，推測此兩型可能是由台灣南方衍生後再向北拓殖。「星狀」結構的基因樹是族群擴張的結果（Page and Holmes，1998），而中性假說測試也呈現族群是從經歷瓶頸效應後正處於族群重新恢復的階段。因此，我們推論台灣的東南方可能是青剛櫟潛在的避難所。

This study examined the spatial pattern of chloroplast DNA (cpDNA) variation in Cyclobalanopsis glauca (Thunb. ex Murray) Oerst. (Fagaceae) in 140 trees from Taiwan (25 populations), Japan (3), Ryukyus (2), Hong Kong (1), and China Mainland (1). By sequencing three cpDNA intergenic spacer fragments using universal primers (trnT-trnL, trnV-trnM, which including trnV intron, and petG-trnP), we found a total of 1980 bp and 15 polymorphic sites. Among them, 12 sites were caused by point mutation, and three resulted from insertion. This gives rise to a total of 13 cpDNA haplotypes. The level of differentiation among the populations studied is relatively high (GST = 0.612). Two ancestral haplotypes (A and B) are widely distributed in East Asia. Interestingly, all the rare cpDNA variations are found only in Taiwan but not in other areas. The Central Mountain Ridge (CMR) of Taiwan creates an unsurpassed barrier to the east-west gene flow of C. glauca. Among the populations on the west of CMR, only three separated populations, Yangmingshan, Wushe, and Chinshuiying, have high haplotype diversity; each consisting of sister haplotypes all mutated from the same ancestral haplotype. Thus, they probably have originated from de novo mutation after the last glacier. This inference agrees with the observation that no spatial autocorrelation existed on the west side. On the east of the CMR, two unrelated dominant lineages (haplotypes D and F) showed significant spatial genetic structure. Estimate of NST-GST was -0.090 and differed significantly from zero. Thus at the local scale, the phylogeographic component of the genetic structure is significant on the east of the CMR. Accompanied with published palynological record of the last glacier, this study suggests the possibility that these two types were colonized northward from the southeastern part of Taiwan. Star-like genealogy is characterized with all the haplotypes coalesce rapidly and actually a general outcome of population expansions (Page and Holmes, 1998). Neutrality test also suggested a demographic expansion recovered from a bottleneck. We, therefore, inferred that the southeastern part of Taiwan might be a potential refugium for C. glauca.