臺灣地區牛樟族群遺傳結構及更新世晚期族群變動事件

The population genetic structure and the late Pleistocene demographic events of Cinnamomum kanehirae Hay. (Lauraceae) in Taiwan

郭大璋(Dai-Chang Kuo)

指導教授 ： 何國傑

國立臺灣大學/生命科學院/植物科學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.10182

摘要

曾經在台灣佔有優勢的特有種牛樟，由於過渡的砍伐，目前已成為希有的闊葉樹種。所用之牛樟植株樣本採集於隸屬台灣林業試驗所六龜分所之營養係採穗園，共分為19個族群、113個個體樣本。利用粒腺體DNA與核基因分析族群內和族群間的遺傳變異，並且討論牛樟的親緣地理。本研究包括二大部份，第一部份為利用粒腺體DNA非編碼區的序列，討論牛樟的親緣地理，並與葉綠體DNA的結果進行比較。第二部份利用核基因研究牛樟族群的分佈，討論最後一次冰盛期（last glacial maximum，LGM）牛樟族群的遷移。
以粒腺體DNA分析而言，整個臺灣島上的牛樟，其π、及θ皆為 0，表示出牛樟族群並沒有親緣地理結構的出現。在粒線體DNA與葉綠體DNA多型性之間的關連性上，有著不顯著的連鎖不平衡。而兩個基因組的其中一個或兩個都發生週期性的突變的清況可能性不大，可能的原因是發生父系傳遞，也有可能是兩個獨立的遺傳事件。
所有族群核基因Chalcone synthase (Chs)的內含子（intron）序列nucleotide diversity (π)平均為0.00716，最小值為0.00372（東南地區SE的錦屏CP族群），最值大為0.00865（西部中心WC的阿里山ALS族群）；Haplotype diversity (Hd)平均為0.841，最小值為0.515（東南地區SE的錦屏CP族群），最值大為1.000（西南地區SW的溪南山HNS族群）。在牛樟族群的分區上，利用SAMOVA估算，將傳統區分的西北地區、西部中心與東南地區的族群，區分在一起形成一個大的群體區域（NW-WC-SE），及一個小的群體區域（SW）。總體而言，牛樟的族群數量的歷史遠比過去認為的還要複雜，已有證據證明族群規模擴張的歷史及最近正面臨瓶頸效應（Table 3.3, Figure 3.4）。而一再發生的基因流、過去空間規模的擴張以及近期發生的瓶頸效應，這一連串事件互相作用的清況下，造成現今牛樟複雜的遺傳結構。
牛樟生長在海拔200~2000公尺之間，而這個範圍內農業過度開發，破壞原始森林的自然棲地。因此，牛樟族群規模的減少，主要是由於人類過度開發所導致的結果。牛樟的保育策略必須以棲地的復原及保存殘存的多樣性為目標，在復育的同時，須考慮到在增加個體到本地原有族群中，而做為這些個體來源的族群需要有最相近的遺傳關連性，以產生有高遺傳變異度的較大族群，避免族群內發生遺傳上的同系繁殖。

關鍵字

牛樟 ； 親緣地理 ； 粒腺體DNA ； Chalcone synthase ； 冰盛期

並列摘要

The once dominant endemic broadleaf tree species in Taiwan, Cinnamomum kanehirae Hay. has become a rare and endangered species due to overcutting. The aim of this study is to characterize the mitochondrial and nuclear DNA sequences, and establish the valuable DNA sequences, genetic diversity, and phylogeography of C. kanehirae. The completion of the study, we should have (1) genetic divergence structure and phylogeographic model of C. kanehirae by mitochondrial DNA non-coding sseuence, and compare with the results of chloroplast DNA data; (2) population syructure and demographic history of C. kanehirae, and migration after last glacial maximum.
To mitochondrial DNA results, the π and θ are all zero, revealed no phylogeographic structure in C. kanehirae. The linkage of the DNA polymorphism between mitochondria and chloroplast, there is not significant linkage disqulilbrium. The two genomes of one or two occurred the possibility of periodic mutation were very low. The possible reasons were paternal inheritance, or two independent genetic events.
Among all of the populations examined nucleotide diversity (π) of the intron of Chalcone synthase (Chs) averaged 0.00716 and ranged from 0.00372 (population CP in the SE region) to 0.00865 (population ALS in the WC region). Haplotype diversity (Hd) averaged 0.841 and ranged from 0.515 (population CP in the SE region) to 1.000 (population HNS in the SW region). Using SAMOVA software to group the population of C. kanehirae, the northwest (NW), west central (WC), and southeast (SE) of the traditional distinctions were grouped into a larger area, and the traditional distinction southwest (SW) is a small area. Consequently, the contemporary genetic structure of C. kanehirae is the outcome of complex interactions among the recurrent gene flow, past spatial range expansion, and a very recent bottleneck.
Elevations where C. kanehirae grows ranges 200~2000 m, and overdevelopment for farming vegetables, tea, and fruit crops has destroyed the natural habitats of primeval forests, including habitats of C. kanehirae. Therefore, loss of the population size of C. kanehirae was mainly caused by human over-exploitation. In consequence, it is essential that this valuable species be conserved through habitat restoration, which can advance the restoration of the effective population size of C. kanehirae. Further field survey to locate plants and grafts for ex situ conservation are another requirement to conserve this species. Management strategies should also consider reinforcing local populations with individuals originating from populations showing the closest genetic relatedness to produce larger population with higher genetic variability. In summary, conservation strategies must therefore aim for habitat restoration and remnant diversity preservation, and avoid the occurrence of genetic inbreeding in populations of C. kanehirae.

並列關鍵字

Cinnamomum kanehirae Hay. ； phylogeography ； mitochondrial DNA ； Chalcone synthase ； last glacial maximum

參考文獻

呂勝由。1996。台灣稀有及瀕危植物之分級—彩色圖鑑(I)。行政院農業委員會。台北市。

黃松根、何坤益、吳國伍、沈勇強、劉文玉。1996。牛樟天然林組成與結構之調查。台灣林業科學11(4):349-360。

Lin TP. 1993. Cinnamomum kanehirae Hay. and Cinnamomum micranthum (Hay.) Hay. Bulletin of Taiwan Forestry Research Institute 8: 11-20.

朱麗萍 2006牛樟、冇樟及樟樹之族群遺傳變異及相關種屬之親緣關係研究。國立臺灣大學森林繫環境資源研究所博士論文。

林讚標 1993 牛樟與冇樟。林業試驗所研究報告季刊，8(1):11-20。