以分子技術探測昆蟲與其擬寄生者間複雜的食物網連結

文獻出處：J HRCEK,SE MILLER, DLJ QUICKE & MA SMITH. 2011. Molecular detection of trophic links in a complex insect host–parasitoid food web. Molecular Ecology Resources. doi: 10.1111/j.1755-0998.2011.03016.x

摘要
過去要揭露昆蟲宿主和其擬寄生物間的關係幾乎只能透過耗時的飼養，而分子方法則只有將對種專一的引子(primers)用在單純的農業害蟲與其擬寄生者系統上。本文報告一種藉由分子偵測巴布亞新幾內亞熱帶雨林內複雜"幼蟲-擬寄生者"食物網的普遍方式。作者對宿主、擬寄生者以及他們的組織殘餘物進行DNA條碼定序，再和當地物種龐大的資料庫進行比對。作者能比對出87% 的宿主序列和36%的擬寄生者序列到物種階層，而其餘則幾乎全部都能判斷到亞科或科的程度。作者運用宿主和擬寄生物雙方的DNA序列分析確認了93個迄今未發現的營養關係，由涉及鱗翅目廣泛科級的37個宿主物種和46個來自膜翅目和雙翅目的擬寄生者物種。由於以幼蟲時期的形態來鑑定宿主物種相單困難，幼蟲也會在飼育過程中死亡，而分子探測對此提供了相當實用的方法。作者甚至偵測到一個極為專一的擬寄生案例，該擬寄生者之宿主桑舞蛾屬(Choreutis)兩個物種在幼蟲形態與生態上沒有任何分別。藉由本研究介紹的方法能夠更加瞭解擬寄生物的宿主專一性，開啓快速調查食物網結構的新可能性，並且能探索尚未預測到的物種交互作用。

Abstract
Previously, host–parasitoid links have been unveiled almost exclusively by time-intensive rearing, while molecular methods were used only in simple agricultural host–parasitoid systems in the form of species-specific primers. Here, we present a general method for the molecular detection of these links applied to a complex caterpillar–parasitoid food web from tropical rainforest of Papua New Guinea. We DNA barcoded hosts, parasitoids and their tissue remnants and matched the sequences to our extensive library of local species. We were thus able to match 87% of host sequences and 36% of parasitoid sequences to species and infer subfamily or family in almost all cases. Our analysis affirmed 93 hitherto unknown trophic links between 37 host species from a wide range of Lepidoptera families and 46 parasitoid species from Hymenoptera and Diptera by identifying DNA sequences for both the host and the parasitoid involved in the interaction. Molecular detection proved especially useful in cases where distinguishing host species in caterpillar stage was difficult morphologically, or when the caterpillar died during rearing. We have even detected a case of extreme parasitoid specialization in a pair of Choreutis species that do not differ in caterpillar morphology and ecology. Using the molecular approach outlined here leads to better understanding of parasitoid host specificity, opens new possibilities for rapid surveys of food web structure and allows inference of species associations not already anticipated.

Keywords: cytochrome oxidase I, Diptera, Hymenoptera, immature stages, Lepidoptera, Papua New Guinea