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.

鸟类拥有复杂的色彩视觉系统，该系统由四种视锥细胞介导，可覆盖包括紫外（ultraviolet, UV）波段在内的宽视觉光谱。多数鸟类拥有由紫敏（violet-sensitive, VS）视锥细胞介导的适度紫外敏感度，这类视锥细胞的敏感峰值位于400~425 nm区间。然而，部分鸟类演化出了更高的紫外敏感度与更宽的视觉光谱，这由紫外敏（ultraviolet-sensitive, UVS）视锥细胞介导，该类细胞的敏感峰值位于360~370 nm区间。视锥细胞类型从VS到UVS的转变原因，及其与视觉生态学的关联，目前仍不明确。已有假说提出，UVS视锥视觉的演化与鸟类羽色相关，使得视觉敏感度与羽毛着色实现“匹配”。这一假说衍生出具体预测：UVS视锥视觉可提升UVS型鸟类的羽色辨别能力，而这一优势在VS型鸟类的羽色辨别中并不存在，或仅表现微弱。本研究借助鸟类UVS视锥细胞的复杂分布数据，结合不同观测条件下的色彩辨别数学模型，对该假说进行了检验。本研究未发现支持该假说的证据，结合既往研究结果来看，这表明UVS视锥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视锥视觉总体上有利于色彩辨别，这为UVS视锥细胞的演化带来了非特异性选择压力。