研究顯示，蛇已經(jīng)進(jìn)化了一種對(duì)致命神經(jīng)毒素的顯著抗性,，而且世界各地蛇的這種抗性都相類(lèi)似,。這一發(fā)現(xiàn)，大大地增加了適應(yīng)遺傳基礎(chǔ)的了解,，是了解適應(yīng)局限性和進(jìn)化程度的模型,。
研究人員發(fā)現(xiàn)，在北美,、中美,、南美及亞洲，那里的蛇能以分泌致命神經(jīng)毒素的兩棲動(dòng)物為食,，這種神經(jīng)毒素就是河豚毒素（tetrodotoxin ,，TTX）。這些蛇的一個(gè)關(guān)鍵鈉通道基因存在有類(lèi)似的突變,，這使蛇對(duì)TTX高度耐受,。突變可以避免TTX阻斷肌肉鈉通道，否則就麻痹蛇的神經(jīng)和肌肉組織,，使蛇不能移動(dòng),。
一個(gè)關(guān)鍵的發(fā)現(xiàn)就是：適應(yīng)性進(jìn)化受參與進(jìn)化反應(yīng)基因的功能特性所限制。雖然有許多可改善適應(yīng)性的可能突變，在這種抗河豚毒素案例中,，許多突變是有代價(jià)的,，因?yàn)橥蛔兏淖兞嘶虻恼９δ堋Ｋ?，在觀(guān)察獨(dú)立適應(yīng)河豚毒素的多個(gè)物種時(shí),，會(huì)看到一個(gè)非常相似且有限的突變。
這一研究結(jié)果發(fā)表在期刊Proceedings of the National Academy of Sciences上,。
生物體如何通過(guò)適應(yīng)進(jìn)化來(lái)應(yīng)對(duì)環(huán)境改變了,？這種適應(yīng)進(jìn)化包含有什么樣的遺傳機(jī)制？這些適應(yīng)性反應(yīng)存在什么限制,？自然界中許多生物都是我們了解這些的模型,。最好的例子就是寄生蟲(chóng)如何獲得耐藥性。
為深入了解,，需要對(duì)更多品種的蛇進(jìn)行研究，并將這些研究推及大量的其他物種,，包括捕食蠑螈毒卵的昆蟲(chóng),。這將拓寬對(duì)適應(yīng)性出現(xiàn)的理解。（生物谷bioon.com）
doi:10.1073/pnas.1113468109
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PMID:
Constraint shapes convergence in tetrodotoxin-resistant sodium channels of snakes
C. R. Feldman, E. D. Brodie, E. D. Brodie, M. E. Pfrender
Natural selection often produces convergent changes in unrelated lineages, but the degree to which such adaptations occur via predictable genetic paths is unknown. If only a limited subset of possible mutations is fixed in independent lineages, then it is clear that constraint in the production or function of molecular variants is an important determinant of adaptation. We demonstrate remarkably constrained convergence during the evolution of resistance to the lethal poison, tetrodotoxin, in six snake species representing three distinct lineages from around the globe. Resistance-conferring amino acid substitutions in a voltage-gated sodium channel, Nav1.4, are clustered in only two regions of the protein, and a majority of the replacements are confined to the same three positions. The observed changes represent only a small fraction of the experimentally validated mutations known to increase Nav1.4 resistance to tetrodotoxin. These results suggest that constraints resulting from functional tradeoffs between ion channel function and toxin resistance led to predictable patterns of evolutionary convergence at the molecular level. Our data are consistent with theoretical predictions and recent microcosm work that suggest a predictable path is followed during an adaptive walk along a mutational landscape, and that natural selection may be frequently constrained to produce similar genetic outcomes even when operating on independent lineages.
