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Abstract：
In the last decades, researchers have been able to determine the molecular basis of some phenotypes, to test for evidence of natural selection upon them, and to demonstrate that the same genes or genetic pathways can be associated with convergent traits. Colour traits are often subject to natural selection because even small changes in these traits can have a large effect on fitness via camouflage, sexual selection or other mechanisms. The melanocortin-1 receptor locus (MC1R) is frequently associated with intraspecific coat colour variation in vertebrates, but it has been far harder to demonstrate that this locus is involved in adaptive interspecific colour differences. Here, we investigate the contribution of the MC1R gene to the colour diversity found in toucans (Ramphastidae). We found divergent selection on MC1R in the clade represented by the genus Ramphastos and that this coincided with the evolution of darker plumage in members of this genus. Using phylogenetically corrected correlations, we show significant and specific relationships between the rate of nonsynonymous change in MC1R (dN) and plumage darkness across Ramphastidae, and also between the rate of functionally significant amino acid changes in MC1R and plumage darkness. Furthermore, three of the seven amino acid changes in MC1R that occurred in the ancestral Ramphastos branch are associated with melanism in other birds. Taken together, our results suggest that the dark colour of Ramphastos toucans was related to nonsynonymous substitutions in MC1R that may have been subject to positive selection or to a relaxation of selective pressure. These results also demonstrate a quantitative relationship between gene and phenotype evolution, representing an example of how MC1R molecular evolution may affect macroevolution of plumage phenotypes.
摘要：
在过去的几十年里，研究人员已经能够确定一些表型的分子基础，为了测试自然选择的证据，并证明相同的基因或遗传途径可以与趋同性状相关。颜色特征通常会受到自然选择的影响，因为即使这些特征的微小变化也会通过伪装对健身产生很大影响，性选择或其他机制。黑皮质素-1受体基因座（MC1R）通常与脊椎动物的种内外壳颜色变化有关，但是很难证明该基因座与适应性种间颜色差异有关。这里,我们研究了MC1R基因对巨嘴鸟（Ramphastidae）中颜色多样性的贡献。我们在以Ramphastos属为代表的进化枝中发现了MC1R的不同选择，这与该属成员中较暗的羽毛的进化相吻合。使用系统发育校正的相关性，我们显示了MC1R（dN）的非同义变化率与整个Ramphastidae的羽毛黑暗之间的显着和特定的关系，以及MC1R中功能显着氨基酸变化的速率和羽毛黑暗之间。此外，在祖先Ramphastos分支中发生的MC1R中的七个氨基酸变化中的三个与其他鸟类的黑色素有关。一起来看,我们的结果表明,Ramphastos巨嘴鸟的深色与MC1R中的非同义替换有关,这些替换可能受到了正向选择或选择性压力的放松.这些结果还证明了基因和表型进化之间的定量关系，代表MC1R分子进化如何影响羽毛表型的宏观进化的一个例子。
