在顯微鏡下,，研究人員觀察到了戲劇性的一幕：一種叫Pristionchus的蛔蟲會咬住另一種線蟲,，并咬出一個開口,，然后吞噬流出的物質(zhì),。
而這場"戰(zhàn)爭"的受害者秀麗隱桿線蟲（Caenorhabditis elegans）并沒有表現(xiàn)出抵御能力,。盡管秀麗隱桿線蟲可能是Pristionchus的一個近親,，但可惜的是，它并沒有同樣堅固的"牙齒",。生物學(xué)家關(guān)注的并不是這種蛔蟲令人印象深刻的捕食技巧,，而是它們口器的形成機(jī)制。
研究人員發(fā)現(xiàn)了這種寄生蟲嘴巴發(fā)育背后的控制機(jī)制：如果該寄生蟲在細(xì)菌充足的環(huán)境下生長,，也就是說環(huán)境中營養(yǎng)素很豐富,，那么它們只會形成非常小的牙齒和窄小的口腔。但如果幼蟲處在一個缺乏食物且高群體強(qiáng)度的環(huán)境下,，則會形成一個寬的嘴巴和堅固的牙齒狀髓石,。
形成寬口和窄口的線蟲并沒有表現(xiàn)出遺傳差異，研究人員表示,，環(huán)境因素支配著它們的口器形成,。
如果幼蟲在發(fā)育階段食物短缺，那么幾乎所有的寄生蟲都會形成寬的,，并武裝有堅固牙齒的嘴巴,。研究表明，該寄生蟲的一種信息素同樣會觸發(fā)這種結(jié)果,?？偟膩碚f，生長環(huán)境食物短缺和群體過剩,，致使這種蛔蟲的一個特殊信號通路被激活,，最終導(dǎo)致堅固牙齒的形成，從而發(fā)生侵略性行為,。研究人員表示他們已經(jīng)識別了控制這種機(jī)制的信號通路,。
Prisionchus堅固的嘴型結(jié)構(gòu)是否使其更適宜于捕獲其他寄生蟲或消耗真菌吸取養(yǎng)分，目前科學(xué)家還只是推斷,，但這項研究表明了自然界生物進(jìn)化的一個重要方式,。(生物谷Bioon.net)
生物谷推薦原文出處：
Nature doi:10.1038/nature09164
Co-option of the hormone-signalling module dafachronic acid–DAF-12 in nematode evolution
Gilberto Bento1, Akira Ogawa1 & Ralf J. Sommer1
Department for Evolutionary Biology, Max-Planck-Institute for Developmental Biology, Spemannstrasse 37; D-72076 Tübingen, Germany
Morphological novelties are lineage-specific traits that serve new functions1, 2. Developmental polyphenisms have been proposed to be facilitators of phenotypic evolution, but little is known about the interplay between the associated genetic and environmental factors3, 4, 5, 6, 7, 8, 9, 10, 11. Here, we study two alternative morphologies in the mouth of the nematode Pristionchus pacificus and the formation of teeth-like structures that are associated with bacteriovorous feeding and predatory behaviour on fungi and other worms12, 13, 14, 15, 16. These teeth-like denticles represent an evolutionary novelty, which is restricted to some members of the nematode family Diplogastridae but is absent from Caenorhabditis elegans and related nematodes14. We show that the mouth dimorphism is a polyphenism that is controlled by starvation and the co-option of an endocrine switch mechanism. Mutations in the nuclear hormone receptor DAF-12 and application of its ligand, the sterol hormone dafachronic acid, strongly influence this switch mechanism. The dafachronic acid–DAF-12 module has been shown to control the formation of arrested dauer larvae in both C. elegans and P. pacificus, as well as related life-history decisions in distantly related nematodes17, 18, 19, 20. The comparison of dauer formation and mouth morphology switch reveals that different thresholds of dafachronic acid signalling provide specificity. This study shows how hormonal signalling acts by coupling environmental change and genetic regulation and identifies dafachronic acid as a key hormone in nematode evolution.
