評論
打印
To find out, they cloned T1R1-T1R3 receptors from a variety of songbirds and tested their responses to sugar. All the receptors they tested—from birds with sugar-rich and sugar-poor diets alike—interacted strongly with sugar molecules. This confirmed that, as with hummingbirds, songbirds regained perception of sweetness via mutations of the gene for T1R1 and T1R3. By contrast, umami receptors cloned from the Tyranni, a sister group to the Passeri, did not interact with sugars, though they did so strongly with amino acids typical of meat. The mutations in the songbird lineage must thus have happened after the Passeri and Tyranni lines diverged, but before the Passeri themselves began proliferating into their current variety.
為了找到答案，他們從各種鳴禽中克隆了T1R1-T1R3受體，并測試了它們對糖的反應。他們測試的所有受體——來自高糖和低糖飲食的鳥類——都與糖分子發生了強烈的相互作用。該研究證實，鳴禽和蜂鳥一樣，通過T1R1和T1R3基因的突變重新獲得了對甜味的感知。相比之下，從霸鹟亞目(雀形目的姐妹群)克隆的鮮味受體不與糖相互作用，雖然他們對肉類中典型的氨基酸有著強烈的反應。因此，鳴禽譜系的突變一定發生在雀形目和霸鹟亞目品種的分化之后，而又在雀形目本身開始繁殖成目前的品種之前。
Intriguingly, when Dr Toda and Dr Baldwin looked at the molecular modifications which allowed the T1R1-T1R3 receptors of hummingbirds and Passeri to detect sweetness, they found them to be completely different. Both, though, involved numerous changes to the underlying DNA, suggesting a strong evolutionary pressure to optimise them. This pressure was probably a consequence of competition to fill the new ecological niches opened up by an ability to recognise sweet things as both edible and nutritious. And it was that which resulted in the Passeri's current diversity. How all this ties up with the mellifluous songs sung by many members of the group is unclear. It may just be a coincidence. But if so, for those who enjoy bird song, it is a fortunate one.
有趣的是，戶田博士和鮑德溫博士研究了使蜂鳥和雀形目的T1R1-T1R3受體感知甜味的分子修飾，結果發現它們是完全不同的。然而，這兩種方法都涉及到基礎DNA的大量變化，這表明有強大的進化壓力來優化它們。這種壓力很可能是人類為了填補新的生態位而展開競爭的結果，這種生態位是人類識別甜味食物既可食用又有營養的能力所開啟的。這也導致了雀形目的多樣性。這一切與該群體許多成員所唱的優美歌曲有何聯系尚不清楚，可能只是一個巧合。但如果是這樣，對于那些喜歡鳥鳴的人來說，這是幸運的。
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