Melin Amanda D, Wells Konstans, Moritz Gillian L, Kistler Logan, Orkin Joseph D, Timm Robert M, Bernard Henry, Lakim Maklarin B, Perry George H, Kawamura Shoji, Dominy Nathaniel J
Department of Anthropology, Dartmouth College, Hanover, NH Department of Anthropology and Archaeology, and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB
Environmental Futures Research Institute, Griffith University, Brisbane, QLD, Australia.
Mol Biol Evol. 2016 Apr;33(4):1029-41. doi: 10.1093/molbev/msv346. Epub 2016 Jan 6.
Debate on the adaptive origins of primates has long focused on the functional ecology of the primate visual system. For example, it is hypothesized that variable expression of short- (SWS1) and middle-to-long-wavelength sensitive (M/LWS) opsins, which confer color vision, can be used to infer ancestral activity patterns and therefore selective ecological pressures. A problem with this approach is that opsin gene variation is incompletely known in the grandorder Euarchonta, that is, the orders Scandentia (treeshrews), Dermoptera (colugos), and Primates. The ancestral state of primate color vision is therefore uncertain. Here, we report on the genes (OPN1SW and OPN1LW) that encode SWS1 and M/LWS opsins in seven species of treeshrew, including the sole nocturnal scandentian Ptilocercus lowii. In addition, we examined the opsin genes of the Central American woolly opossum (Caluromys derbianus), an enduring ecological analogue in the debate on primate origins. Our results indicate: 1) retention of ultraviolet (UV) visual sensitivity in C. derbianus and a shift from UV to blue spectral sensitivities at the base of Euarchonta; 2) ancient pseudogenization of OPN1SW in the ancestors of P. lowii, but a signature of purifying selection in those of C. derbianus; and, 3) the absence of OPN1LW polymorphism among diurnal treeshrews. These findings suggest functional variation in the color vision of nocturnal mammals and a distinctive visual ecology of early primates, perhaps one that demanded greater spatial resolution under light levels that could support cone-mediated color discrimination.
关于灵长类动物适应性起源的争论长期以来一直聚焦于灵长类视觉系统的功能生态学。例如，据推测，赋予色觉的短波（SWS1）和中长波敏感（M/LWS）视蛋白的可变表达可用于推断祖先的活动模式，进而推断选择性生态压力。这种方法存在的一个问题是，在总目真灵长大目中，即树鼩目（树鼩）、皮翼目（鼯猴）和灵长目，视蛋白基因变异情况尚不完全清楚。因此，灵长类动物色觉的祖先状态尚不确定。在此，我们报告了七种树鼩中编码SWS1和M/LWS视蛋白的基因（OPN1SW和OPN1LW），其中包括唯一的夜行性树鼩——笔尾树鼩。此外，我们还研究了中美绵毛负鼠（Caluromys derbianus）的视蛋白基因，它是灵长类起源争论中一个持久的生态类似物。我们的结果表明：1）中美绵毛负鼠保留了紫外视觉敏感性，而在真灵长总目基部从紫外光谱敏感性转变为蓝光光谱敏感性；2）笔尾树鼩祖先中OPN1SW发生了古老的假基因化，但中美绵毛负鼠的祖先中有纯化选择的特征；3）日行性树鼩中不存在OPN1LW多态性。这些发现表明夜行性哺乳动物色觉存在功能变异，以及早期灵长类动物独特的视觉生态学，或许这种视觉生态学要求在能够支持视锥介导的颜色辨别光水平下具有更高的空间分辨率。
