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科技板塊
The origin of songbirds
鳴禽的起源
The sweet taste of success
成功的甜蜜滋味
Songbirds can detect sugar. That may explain their ubiquity
鳴禽可以探測到糖，這或許可以解釋它們無處不在的原因
Imagine a world without bird song. Yet this might have come about if it had not been for a genetic change that happened some 30m years ago, at the beginning of the evolution of the Passeri, to give songbirds their proper name.
想象一個沒有鳥兒歌唱的世界。然而，如果不是大約3000萬年前雀形目進化初期發生的基因變化給了鳴禽真正的名字，可能這個世界就真的沒有鳥兒歌唱。
Birds evolved from carnivorous dinosaurs called theropods. Meat eaters need not detect sugar in the way that, say, fruit eaters do, and genetic analyses of modern birds suggest their theropod ancestor had lost the ability to taste sweetness. Today, however, many birds have sugar-rich diets of nectar or fruit, so perceiving things as sweet is a useful attribute. And research just published in Science by Toda Yasuka of Tokyo University and Maude Baldwin of the Max Planck Institute for Ornithology in Seewiesen, Germany, suggests songbirds can indeed perceive sweetness. This reevolved ability may have been instrumental in their success. Since almost half the bird species now alive are Passeri, that is no small matter.
鳥類是從食肉恐龍進化而來的。肉食者不需要像水果食者那樣檢測糖分，對現代鳥類的基因分析表明，它們的獸腳亞目祖先已經失去了品嘗甜味的能力。然而，今天，許多鳥類以富含糖分的花蜜或水果為食，所以“感知事物是甜的”是一個有用的屬性。東京大學的戶田康嘉和德國許威森的Max Planck鳥類研究所的莫德·鮑爾溫剛剛在《科學》雜志上發表了一項研究，表明鳴禽確實能夠感知甜味。這種再進化的能力可能對它們的成功起到了重要作用。因為現在幾乎一半的鳥類都是雀形目，這不是一件小事。
Vertebrates' taste-receptor genes normally include three that encode proteins called T1R1, T1R2 and T1R3. The taste receptors themselves are formed from pairs of these proteins. Receptors for sweetness are a combination of T1R2 and T1R3. Birds, however, lack the gene for T1R2. Presumably, it was lost by their theropod ancestors, which did not need it. Dr Toda's and Dr Baldwin's experiments have shown how this loss was reversed.
脊椎動物的味覺受體基因通常包括三個編碼T1R1、T1R2和T1R3的蛋白質。味覺感受器本身就是由這些成對的蛋白質組成的。甜味受體是T1R2和T1R3的組合。然而，鳥類缺乏T1R2基因。據推測，它是獸腳亞目動物的祖先遺失的，它們并不需要它。戶田博士和鮑德溫博士的實驗顯示了這種損失是如何逆轉的。
The pair's first study, published in 2014, was on hummingbirds, which feed on nectar from flowers. It found that hummingbirds regained the ability to taste sugars via mutations in the genes for T1R1 and T1R3. The receptor formed by combining T1R1 and T1R3 normally detects umami, a savoury flavour typical of meat. In hummingbirds, these mutations allow this receptor to detect sugars, too. Dr Toda and Dr Baldwin therefore wondered whether that was also the case for songbirds.
他們的第一個研究發表于2014年，研究對象是以花蜜為食的蜂鳥。研究發現，蜂鳥通過T1R1和T1R3基因的突變重新獲得了嘗糖的能力。由T1R1和T1R3組合而成的受體通常能檢測鮮味，即肉的一種典型的咸味。在蜂鳥身上，這些突變也讓這種受體能夠檢測糖。戶田博士和鮑德溫博士因此想知道鳴禽的情況是否也是如此。
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