敏銳的嗅覺將幫助梟鸚在黑暗中找到食物,。（圖片提供:Don Merton）
誰都曉得鷹具有銳利的視覺,，而貓頭鷹則因敏銳的聽覺被人們所知，但是鳥類卻很少因?yàn)樾嵊X為自己攬得好名聲,。如今,，隨著針對大量鳥類的嗅覺基因進(jìn)行的首個(gè)分析結(jié)果的出臺，這一切都將發(fā)生改變,。研究發(fā)現(xiàn),，鳥類的鼻子可能比人們想象得更靈敏,。
人們對鳥類行為的興趣使得研究人員較多關(guān)注它們?nèi)A麗的交配儀式、音調(diào)優(yōu)美的歌聲以及其他天賦,，但鳥類的嗅覺卻在很大程度上被科學(xué)家忽視了,。僅有的少量研究表明，嗅覺在鳥類行為中扮演了一個(gè)角色,，但對其背后的生物學(xué)機(jī)制知之甚少,。
在一項(xiàng)新的研究中，由德國馬普學(xué)會鳥類研究所的分子生態(tài)學(xué)家Silke Steiger和她的研究生Bart Kempenaers領(lǐng)導(dǎo)的一個(gè)研究小組,，對鳥類系譜圖的7個(gè)主要分支中的9種鳥的嗅覺基因進(jìn)行了研究,。研究人員的工作主要集中于尋找與編碼嗅覺受體——負(fù)責(zé)感知?dú)馕?mdash;—有關(guān)的基因,。研究人員通常假設(shè),，動物具有的受體越多則它們的嗅覺能力越強(qiáng)。例如,，小鼠擁有將近1000個(gè)運(yùn)轉(zhuǎn)的嗅覺受體基因,，而人類則大約攜帶了400個(gè)這樣的基因。
根據(jù)這一邏輯,，在Steiger所分析的鳥類中,，嗅覺最靈敏的是梟鸚——一種罕見的在夜間活動的新西蘭鸚鵡。研究小組發(fā)現(xiàn)梟鸚具有667個(gè)功能性嗅覺受體基因,。另一種在夜間活動的新西蘭鳥類——褐鷸鴕——大約攜帶了600種功能性受體基因,。Steiger相信，敏銳的嗅覺將幫助這些鳥類在夜晚找到食物,。粉紅鳳頭鸚鵡——一種生活在澳大利亞的鸚鵡,，其嗅覺功能并未經(jīng)過研究——在這些鳥類中排名墊底，據(jù)估計(jì),，它只有107個(gè)運(yùn)轉(zhuǎn)的嗅覺受體基因,。研究人員在7月15日的英國《皇家學(xué)會學(xué)報(bào)B》網(wǎng)絡(luò)版上報(bào)告了這一研究成果。Steiger表示：“鳥類的嗅覺水平可能與人類相當(dāng),，甚至要更強(qiáng)一些,。”但是她強(qiáng)調(diào)，基因數(shù)量僅僅是一個(gè)粗略的指標(biāo),。要想搞清鳥類的嗅覺功能,，還需要進(jìn)行更多的遺傳學(xué)和行為學(xué)研究。
美國哈佛大學(xué)的進(jìn)化生物學(xué)家Scott Edwards表示：“這項(xiàng)研究是一個(gè)分子證據(jù),，表明鳥類的嗅覺受體真的能夠發(fā)揮作用。”加利福尼亞大學(xué)戴維斯分校的感知生態(tài)學(xué)家Gabrielle Nevitt強(qiáng)調(diào),，這一發(fā)現(xiàn)填補(bǔ)了正在充實(shí)的行為學(xué)研究的證據(jù),，證明了許多鳥類利用它們的嗅覺尋找食物、躲避天敵以及選擇配偶。（生物谷Bioon.com）
生物谷推薦原始出處：
Proceedings of the Royal Society B,，10.1098/rspb.2008.0607,，Silke S. Steiger, Bart Kempenaers
Avian olfactory receptor gene repertoires: evidence for a well-developed sense of smell in birds?
1Department of Behavioural Ecology and Evolutionary Genetics, Max-Planck Institute for Ornithology, PO Box 1564, 82319 Starnberg, Germany
2 Cawthron Institute, Private Bag 2, Nelson 7042, New Zealand
摘要
Among vertebrates, the sense of smell is mediated by olfactory receptors (ORs) expressed in sensory neurons within the olfactory epithelium. Comparative genomic studies suggest that the olfactory acuity of mammalian species correlates positively with both the total number and the proportion of functional OR genes encoded in their genomes. In contrast to mammals, avian olfaction is poorly understood, with birds widely regarded as relying primarily on visual and auditory inputs. Here, we show that in nine bird species from seven orders (blue tit, Cyanistes caeruleus; black coucal, Centropus grillii; brown kiwi, Apteryx australis; canary, Serinus canaria; galah, Eolophus roseicapillus; red jungle fowl, Gallus gallus; kakapo, Strigops habroptilus; mallard, Anas platyrhynchos; snow petrel, Pagodroma nivea), the majority of amplified OR sequences are predicted to be from potentially functional genes. This finding is somewhat surprising as one previous report suggested that the majority of OR genes in an avian (red jungle fowl) genomic sequence are non-functional pseudogenes. We also show that it is not the estimated proportion of potentially functional OR genes, but rather the estimated total number of OR genes that correlates positively with relative olfactory bulb size, an anatomical correlate of olfactory capability. We further demonstrate that all the nine bird genomes examined encode OR genes belonging to a large gene clade, termed γ-c, the expansion of which appears to be a shared characteristic of class Aves. In summary, our findings suggest that olfaction in birds may be a more important sense than generally believed.
