Data from: Visual modelling suggests a weak relationship between the evolution of ultraviolet vision and plumage colouration in birds

Birds have sophisticated colour vision mediated by four cones types that cover a wide visual spectrum including ultraviolet (UV) wavelengths. Many birds have modest UV-sensitivity provided by violet-sensitive (VS) cones with sensitivity maxima between 400-425 nm. However, some birds have evolved higher UV-sensitivity and a larger visual spectrum given by UV-sensitive (UVS) cones maximally sensitive at 360-370 nm. The reasons for VS-UVS transitions and their relationship to visual ecology remain unclear. It has been hypothesized that the evolution of UVS-cone vision is linked to plumage colours so that visual sensitivity and feather colouration are “matched”. This leads to the specific prediction that UVS-cone vision enhance the discrimination of plumage colours of UVS-birds while such an advantage is absent or less pronounced for VS-bird colouration. We test this hypothesis using knowledge of the complex distribution of UVS-cones among birds combined with mathematical modelling of colour discrimination during different viewing conditions. We find no support for the hypothesis, which, combined with previous studies suggests only a weak relationship between UVS-cone vision and plumage colour evolution. Instead we suggest that UVS-cone vision generally favours colour discrimination, which creates a non-specific selection pressure for the evolution of UVS-cones.

鸟类拥有复杂的色觉，该视觉由四种覆盖包括紫外线（ultraviolet, UV）波段在内的宽光谱视锥细胞（cone）介导。许多鸟类依靠敏感度峰值介于400~425 nm的紫罗兰敏感（violet-sensitive, VS）视锥细胞，实现中等程度的紫外线敏感度。然而，部分鸟类演化出了更高的紫外线敏感度与更宽的视觉光谱，这一特性由敏感度峰值位于360~370 nm的紫外线敏感（ultraviolet-sensitive, UVS）视锥细胞所赋予。VS与UVS表型转换的成因及其与视觉生态的关联仍不明确。有假说提出，UVS视锥细胞视觉的演化与羽色相关联，使得视觉敏感度与羽毛着色实现“匹配”。由此可得到一项特定预测：UVS视锥细胞视觉能够提升UVS鸟类的羽色辨别能力，而该优势在VS鸟类的羽色识别中并不存在，或仅表现较弱。我们借助鸟类UVS视锥细胞的复杂分布数据，结合不同观测条件下的色觉辨别数学模型，对该假说进行了检验。我们未发现支持该假说的证据，结合既往研究来看，这表明UVS视锥细胞视觉与羽色演化之间仅存在微弱关联。与之相反，我们提出UVS视锥细胞视觉整体上有利于色觉辨别，这为UVS视锥细胞的演化带来了非特异性的选择压力。