Reexamination of the Pattern of Geographical Disjunction of Chamaecyparis (Cupressaceae) in North America and East Asia

重新審視扁柏屬植物北美與東亞之間斷分布

廖培鈞(Pei-Chun Liao) ； 林讚標(Tsan-Piao Lin) ； 黃士穎(Shih-Ying Hwang)

《Botanical Studies》 51卷4期 (2010/10) Pp. 511-520

摘要

全世界的扁柏屬植物共有六個分類群，分布在北美及東亞地區。根據以往以葉綠體DNA進行的親緣關係研究指出現存的扁柏屬植物經歷過兩次的獨立起源，並分別從北美遷移至東亞。然而藉由形態及核DNA建構的親緣樹卻呈現不一致的結果。本研究中，我們重新定序了葉綠體matK基因序列，並從基因資料庫(NCBI)下載其他序列重新建構扁柏屬的親緣關係，並擬重新確認扁柏屬植物的生物地理模式。以matK重建之基因樹與先前依據葉綠體DNA所得結果一致，但不同於以rbcL和ITS重建之基因樹。rbcL基因缺乏足夠的變異資訊位點，故可能造成譜系檢選與其他葉綠體DNA不一致；而ITS的結果與前人研究相悖，顯示ITS可能受到多重拷貝造成的非同源性及網狀演化（基因重組或漸滲雜交）影響，而降低親緣關係推論之可信度。同質化分檢測(PHT)亦證實葉綠體DNA與核DNA可能經歷不一致的演化歷程，故不建議將序列合併分析。根據葉綠體DNA序列所得之親緣假說（matK型基因樹），以DIVA進行之儉約法分析併以化石紀錄及地質證據，推論現存的扁柏屬植物經歷過兩次獨立的遷移事件，最有可能的起源地位於北美洲，經由白令陸橋抵達東亞的日本及台灣。此推論支持前人以葉綠體DNA為基礎所作之生物地理推論。而以核DNA建構之基因樹則可能受雙親遺傳等交錯的演化關係影響，故以核DNA進行生物地理探討時需格外謹慎。

關鍵字

扁柏屬 ； 間斷分布 ； 親緣關係 ； matK

並列摘要

The genus Chamaecyparis (Cupressaceae) is comprised of six taxa native to East Asia and North America. Two independent lineages from eastern North America to East Asia and from western North America to East Asia have been identified from phylogenetic analyses based on variation in plastid DNA (ptDNA). However, the trees inferred from a nuclear ribosomal internal transcribed spacer (nrITS), the NEEDLY intron 2, and combined data from genetic and morphological characters of other studies are incongruent with the tree inferred from ptDNA. In this study, we sequenced the plastid matK gene as well as other sequences acquired from GenBank including the matK, rbcL, and nrITS sequences to reconstruct the phylogenetic trees of Chamaecyparis. The phylogenetic topology inferred from matK was congruent with the previous inference obtained using other ptDNA markers while the rbcL and ITS trees were congruent with previously inferred trees using the combined data and ITS sequences, respectively. Relatively less-(rbcL) and more-informative sites (ITS) may lead to different lineage sorting and incongruent phylogenetic topologies, which were evidenced by rejection of evolutionary homogeneity between ptDNA and ITS sequences in the partition homogeneity test. The phylogenetic tree reconstructed using matK and other ptDNA strongly supports the geographically disjunct distribution of Chamaecyparis in North America and East Asia. A dispersal-vicariance analysis, and geologic and fossil evidence indicated that at least two independent dispersal events occurred from North America to East Asia, which support the previous biogeographic inference by ptDNA. The use of biparental inherited markers for biogeographic inferences should be done with caution.

並列關鍵字

Chamaecyparis ； Geographical disjunction ； Phylogenetic relationships ； matK