蘇鐵綺灰蝶的來源檢測與綺灰蝶屬食性演化之研究

Abstract

因食物或園藝造景之用而引入的外來植物，雖然不一定會直接危害原生物種的生存，但可能間接地影響到利用這些植物的昆蟲，進而改變其演化過程。以蘇鐵綺灰蝶(Chilades pandava)為例：自1990年以來，台灣地區引入大量的蘇鐵屬(Cycas)植物作為庭園造景之用，直接或間接地造成蘇鐵綺灰蝶的族群快速擴張，現今已分佈全台。本論文的第一部分以蘇鐵綺灰蝶的事件來討論外來園藝植物對原生昆蟲族群之遺傳結構的影響，並追溯大發生族群的來源。 綺灰蝶屬的成員為體型最小的蝴蝶之一，分佈範圍可從非洲西部橫跨到亞洲東部，並且除了一般專食豆科及芸香科植物的蝶種外，亦包含有較罕見的專食蘇鐵科植物的成員。由於綺灰蝶屬的分佈範圍和食草的利用關係並不常見於其它屬的蝴蝶中，因此懷疑綺灰蝶屬是否為單系群(monophyly)。本論文將在第二部分討論綺灰蝶屬成員的親緣關係，以暸解此屬的食草利用格局。 第一部份將世界各地共810隻蘇鐵綺灰蝶樣本，進行粒線體COII序列分析，得有29個基因型，其中台灣各地大發生的族群所擁有的主要基因型C僅分佈在台灣。此結果支持台灣各地大發生的族群來自島內族群擴張，並非人為引進蘇鐵時所夾帶的外來族群；在第二部分，為了建構綺灰蝶屬內的成員以及食性利用之間的關係，共採用13種綺灰蝶屬的成員以及42種近緣的蝴蝶作為分析(3437bp, 82 taxa)，發現目前歸類為綺灰蝶屬的蝴蝶並非單系群。但若將處理為同物異名的晶灰蝶屬(Freyeria)獨立出來，則綺灰蝶屬為單系群。儘管綺灰蝶屬仍包括利用裸子及被子植物的種類，但是利用蘇鐵為食的成員自成一群，顯示以蘇鐵為食的行為為單一的寄主轉移事件。 此論文的結果架構出台灣地區蘇鐵綺灰蝶之擴散來源，同時指出外來園藝植物之引進使得蘇鐵綺灰蝶的角色轉變為園藝害蟲，並可能加害原生種台東蘇鐵的生存，建議長期監控園藝蘇鐵的貿易方能保護原生蘇鐵之生存。而根據分子親緣關係樹，我們將晶灰蝶屬自綺灰蝶屬中獨立出來，不僅指出綺灰蝶屬可能為非洲起源的類群，並且提供灰蝶親緣關係最複雜的類群之一―藍灰蝶組(Eliot’s Polyommatus section)重建其屬級分類的可能性。

Foreign plants are usually introduced for food or aesthetic reasons. Most of these plants are non-invasive, but can alter the evolutionary trajectory of the associated native insects or inadvertently spread potential pests. A hitherto poorly documented example is the rapid expansion of Chilades pandava, a Cycas-feeding butterfly. Since about 1990, large numbers of the Sago Palm Cycas revoluta were introduced into Taiwan. Invading or introduced with this hostplant, Ch. pandava has rapidly spread to all major parts of Taiwan and to other places worldwide. In order to trace the source of outbreaks, I set this issue as the first part of this dissertation (Part I). In part II, the members in the genus Chilades include some of the smallest butterflies in the world. As for some other small butterflies classified in the same lycaenid tribe, Polyommatini, they are widely distributed, ranging from West Africa to East Asia. Larval hostplant associations are unusually wide for a single butterfly genus, including both gymnosperms and angiosperms, questioning the monophyly of Chilades butterflies and the hostplant associations among this genus butterflies. In part I, total 810 specimens were sampled covering 50 Taiwanese localities and other regions using mitochondrial COII sequences. Only 29 haplotypes were found, however, the haplotype C which dominates outbreak populations from western Taiwan was endemic to the island. This is consistent with the hypothesis of a local range expansion of Ch. pandava, rather than an introduction. In addition, the Taiwanese Central Mountain Ridge may constitute a primary biogeographic barrier restricting gene flow between eastern and western populations. In part II, to reconstruct the relationships of the genus Chilades and map patterns of hostplant use onto this inferred tree, mitochondrial COI, COII and nuclear EF-1α sequences (3437 bp, total 82 taxa) were used. The topologies show that Chilades is polyphyletic containing two separated clades, and that gymnosperm specialists (feeding on cycads) are monophyletic and represent a single host shift from angiosperms (Fabaceae). The study of tracing the source of outbreaks populations not only flags an important new invasive insect that needs to be monitored and controlled within the horticultural trade and for in situ cycad conservation, but also provides a clearly documented case of the transformation of a native tropical butterfly into a pest via introduced horticultural plants. In the aspect of genus status, once butterflies belonging to the genus Freyeria (which is usually treated as synonym of Chilades, but is here resurrected, including Freyeria putli, F. minuscula, F. trochylus, and F. yunnanensis comb. nov.) are excluded, the genus Chilades becomes monophyletic, but still comprising both angiosperm and gymnosperm (cycad) feeders. In this part, I infer the correct phylogenetic placement of both Chilades and Freyeria, African origins for Chilades, and also an aspect to reconstructing the genera relationships among Eliot’s Polyommatus section.