ARC Centre of Excellence in Vision Science, Research School of Biology, ANU College of Medicine, Biology and Environment, The Australian National University, Canberra, Australia.
PLoS One. 2010 Dec 6;5(12):e14231. doi: 10.1371/journal.pone.0014231.
Color vision in marsupials has recently emerged as a particularly interesting case among mammals. It appears that there are both dichromats and trichromats among closely related species. In contrast to primates, marsupials seem to have evolved a different type of trichromacy that is not linked to the X-chromosome. Based on microspectrophotometry and retinal whole-mount immunohistochemistry, four trichromatic marsupial species have been described: quokka, quenda, honey possum, and fat-tailed dunnart. It has, however, been impossible to identify the photopigment of the third cone type, and genetically, all evidence so far suggests that all marsupials are dichromatic. The tammar wallaby is the only Australian marsupial to date for which there is no evidence of a third cone type. To clarify whether the wallaby is indeed a dichromat or trichromatic like other Australian marsupials, we analyzed the number of cone types in the "dichromatic" wallaby and the "trichromatic" dunnart. Employing identical immunohistochemical protocols, we confirmed that the wallaby has only two cone types, whereas 20-25% of cones remained unlabeled by S- and LM-opsin antibodies in the dunnart retina. In addition, we found no evidence to support the hypothesis that the rod photopigment (rod opsin) is expressed in cones which would have explained the absence of a third cone opsin gene. Our study is the first comprehensive and quantitative account of color vision in Australian marsupials where we now know that an unexpected diversity of different color vision systems appears to have evolved.
有袋动物的色觉最近成为哺乳动物中一个特别有趣的案例。在亲缘关系密切的物种中，既有二色视者，也有三色视者。与灵长类动物不同，有袋动物似乎进化出了一种与 X 染色体无关的不同类型的三色视。基于微分光光度法和视网膜全层免疫组织化学，已经描述了四种三色有袋动物物种：短尾矮袋鼠、袋熊、蜜袋鼯和胖尾袋貂。然而，一直无法确定第三类视锥细胞的光色素，而且从遗传学角度来看，迄今为止所有的证据都表明所有有袋动物都是二色视者。塔马尔沙袋鼠是唯一一种没有第三类视锥细胞证据的澳大利亚有袋动物。为了澄清沙袋鼠是否确实像其他澳大利亚有袋动物一样是二色视者或三色视者，我们分析了“二色视”沙袋鼠和“三色视”袋貂的视锥细胞类型数量。我们采用相同的免疫组织化学方案，证实沙袋鼠只有两种视锥细胞类型，而在袋貂视网膜中，20-25%的视锥细胞未被 S-和 LM-opsin 抗体标记。此外，我们没有发现任何证据支持视杆光色素（视杆视蛋白）在视锥细胞中表达的假设，这将解释为什么没有第三种视锥细胞视蛋白基因。我们的研究是首次对澳大利亚有袋动物色觉进行全面和定量的描述，现在我们知道，一种意想不到的不同色觉系统多样性似乎已经进化出来了。
