Key Laboratory of Zoonosis of Liaoning Province, College of Animal Science and Veterinary Medicine, Shenyang Agricultural University, Shenyang, China.
School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
Mol Biol Evol. 2018 May 1;35(5):1130-1134. doi: 10.1093/molbev/msy019.
The visual ability and associated photic niche of early mammals is debated. The theory that ancestral mammals were nocturnal is supported by diverse adaptations. However, others argue that photopigment repertoires of early mammals are more consistent with a crepuscular niche, and support for this also comes from inferred spectral tuning of middle/long wavelength-sensitive (M/LWS) opsin sequences. Functional studies have suggested that the M/LWS pigment in the ancestor of Mammalia was either red- or green-sensitive; however, these were based on outdated phylogenies with key lineages omitted. By performing the most detailed study to date of middle/long-wave mammalian color vision, we provide the first experimental evidence that the M/LWS pigment of amniotes underwent a 9-nm spectral shift towards shorter wavelengths in the Mammalia ancestor, exceeding predictions from known critical sites. Our results suggest early mammals were yellow-sensitive, possibly representing an adaptive trade-off for both crepuscular (twilight) and nocturnal (moonlight) niches.
早期哺乳动物的视觉能力和相关的光生态位存在争议。认为祖先进化的哺乳动物是夜行性动物的理论得到了多种适应性的支持。然而，也有人认为早期哺乳动物的视色素谱更符合黄昏生态位，从中推断出中/长波长敏感（M/LWS）视蛋白序列的光谱调谐也支持这一观点。功能研究表明，哺乳类动物祖先的 M/LWS 色素是红色或绿色敏感的；然而，这些研究是基于过时的系统发育，其中关键的谱系被省略了。通过对中/长波哺乳动物颜色视觉进行迄今为止最详细的研究，我们提供了第一个实验证据，证明在哺乳动物祖先中，羊膜动物的 M/LWS 色素向较短波长方向发生了 9nm 的光谱位移，超出了已知关键位点的预测。我们的研究结果表明，早期哺乳动物对黄色敏感，这可能是对黄昏（曙光）和夜间（月光）生态位的一种适应性权衡。
