School of Life Sciences, East China Normal University, Shanghai 200062, China.
Mol Biol Evol. 2010 Nov;27(11):2642-50. doi: 10.1093/molbev/msq152. Epub 2010 Jun 17.
Taste perception is an important component of an animal's fitness. The identification of vertebrate taste receptor genes in the last decade has enabled molecular genetic studies of the evolution of taste perception in the context of the ecology and dietary preferences of organisms. Although such analyses have been conducted in a number of species for bitter taste receptors, a similar analysis of sweet taste receptors is lacking. Here, we survey the sole sweet taste-specific receptor gene Tas1r2 in 42 bat species that represent all major lineages of the order Chiroptera, one of the most diverse groups of mammals in terms of diet. We found that Tas1r2 is under strong purifying selection in the majority of the bats studied, with no significant difference in the strength of the selection between insect eaters and fruit eaters. However, Tas1r2 is a pseudogene in all three vampire bat species and the functional relaxation likely started in their common ancestor, probably due to the exclusive feeding of vampire bats on blood and their reliance on infrared sensors rather than taste perception to locate blood sources. Our survey of available genome sequences, together with previous reports, revealed additional losses of Tas1r2 in horse, cat, chicken, zebra finch, and western clawed frog, indicating that sweet perception is not as conserved as previously thought. Nonetheless, we found no common dietary pattern among the Tas1r2-lacking vertebrates, suggesting different causes for the losses of Tas1r2 in different species. The complexity of the ecological factors that impact the evolution of Tas1r2 calls for a better understanding of the physiological roles of sweet perception in different species.
味觉感知是动物适应能力的一个重要组成部分。在过去的十年中，脊椎动物味觉受体基因的鉴定使得我们能够在生态和生物的饮食偏好的背景下，从分子遗传学的角度研究味觉感知的进化。虽然已经在许多物种中对苦味受体进行了这样的分析，但缺乏对甜味受体的类似分析。在这里，我们调查了 42 种蝙蝠物种中的唯一甜味特异性受体基因 Tas1r2，这些蝙蝠代表了翼手目（Chiroptera）这一在饮食方面是哺乳动物中最多样化的目之一的所有主要谱系。我们发现，Tas1r2 在大多数研究的蝙蝠中受到强烈的纯化选择，食虫动物和食果动物之间的选择强度没有显著差异。然而，Tas1r2 在所有三种吸血蝙蝠物种中都是假基因，功能放松很可能在它们的共同祖先中就开始了，这可能是由于吸血蝙蝠专门以血液为食，并且依赖于红外线传感器而不是味觉感知来定位血液来源。我们对可用基因组序列的调查，以及以前的报告，揭示了在马、猫、鸡、斑马雀和西部爪蟾中 Tas1r2 的额外缺失，这表明甜味感知并不像以前认为的那样保守。尽管如此，我们在没有 Tas1r2 的脊椎动物中没有发现共同的饮食模式，这表明不同物种中 Tas1r2 的缺失有不同的原因。影响 Tas1r2 进化的生态因素的复杂性要求我们更好地理解不同物种中甜味感知的生理作用。
