以質體基因組重建太平洋構樹的傳播

構樹〔Broussonetia papyrifera (L.) L’Hér. ex Vent., paper mulberry〕為雌雄異株之喬木，纖維強韌可作為造紙用途，在南島語族的文化當中，是製作樹皮布的重要材料，因此隨著南島語族的遷徙而傳播出原生地範圍。近年來，隨著更多的考古學、語言學、古DNA基因體學等證據逐漸發表，南島語族最早的原鄉可追溯至臺灣。然而各家學者爭論不休的是南島語族為何冒險遷徙，是因為農業發展，造成人口上升後被迫向外遷徙的農業/語言擴張假說；還是為了貿易而展開長距離的遷徙？鑒於構樹在太平洋地區完全由人為傳播，且為無性繁殖，加之其為原生於大陸東南與臺灣，因此可從構樹的親緣地理學，推論南島語族的遷徙，並檢測南島語族遷徙的動力是否符合農業/語言擴張假說。本研究利用次世代定序的基因略讀策略與標靶基因獲取 (Bait capture)，取得構樹完整的質體基因組序列，並藉由重建最大似然性的親緣關係及基因單倍型網絡圖，推敲太平洋構樹的傳播路徑。據分析，構樹自臺灣被攜出後，經過蘇拉威西向東傳至巴布亞新幾內亞，再經由東加、斐濟與薩摩亞，最後到達夏威夷與復活節島。藉由分析質體基因組，發現太平洋群島的構樹可分為三群：近大洋洲、遠大洋洲的東、西半部。親緣關係分析結果中，夏威夷的構樹具有三群結構，推測為三次不同引入歷史造成，分別為夏威夷最原始的構樹，與馬克薩斯群島親緣關係接近；與東加、斐濟、薩摩亞相近的近代引入構樹；以及可能由夏威夷當時外來勞動力所引入的構樹，其基因單倍型為cp41。而夏威夷cp41與中國cp28與cp32關係接近，依據親緣關係分析，推測為自中國大陸東南沿海一帶引入。依據構樹質體基因組的親緣關係分析，再次印證了出臺灣說，亦支持迫使南島語族向外遷徙的動力為農業擴張假說。

關鍵字

南島語族遷徙；出臺灣說；農業擴張假說；共生物種；構樹；次世代定序；質體基因組

並列摘要

Paper mulberry [Broussonetia papyrifera (L.) L’Hér. ex Vent.], a dioecious tree native to East Asia, is a cultural necessity of Austronesian-speaking peoples (Austronesians) for making barkcloth (tapa). By studying the phylogeography of the Pacific paper mulberries, the migration path of the Austronesians can be deduced. Recent linguistic, archaeological, and paleogenomic studies support Taiwan as the Austronesian ancestral homeland, though the ultimate causes of Austronesian migration remain debated. The Farming/Language Dispersal Hypothesis posits that population growth triggered by the adoption of agricultural lifestyle had led to increased competition for land and thus forcing outward migration. Alternatively, some argued that maritime trade had motivated Austronesians’ epic migration. Paper mulberry, clonally propagated for making barkcloth, provide an ideal commensal species for testing hypotheses of Austronesian expansion and migrations. This study employed the strategies of genome skimming and bait-capture of the Next-generation sequencing technique to assemble complete plastome sequences of paper mulberry and reconstruct routes of paper mulberry’s transportation in the Pacific based on maximum likelihood tree, dated phylogeny, and haplotype networks. Our analyses revealed that the Pacific paper mulberry was originated in Taiwan and transported into Pacific islands via Sulawesi, New Guinea, Fiji, Tonga, and Samoa, with Hawaii and Rapa Nui as the final destination. Our data also show three independent origins of the Hawaiian paper mulberry, including the ancient introduction by Polynesian voyagers from Marquesas, recent reintroduction from Tonga, Fiji, and Samoa for the revival of barkcloth culture, and likely a recent introduction from southeastern China likely associated with recent immigrants. Our data is highly congruent with the routes of Austronesian migration proposed by the “Out of Taiwan” hypothesis and supports that paper mulberry has been propagated since the ancient time in the Pacific, further attesting the Farming/Language Dispersal Hypothesis.

並列關鍵字

paper mulberry ； Austronesians migration ； Farming/Language Dispersal Hypothesis ； NGS ； Plastome

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以質體基因組重建太平洋構樹的傳播

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