School of Life Sciences, University of Nottingham, Nottingham, NG7 2RD, UK.
Heredity (Edinb). 2019 Aug;123(2):162-175. doi: 10.1038/s41437-019-0189-z. Epub 2019 Feb 26.
Biologists have long tried to describe and name the different phenotypes that make up the shell polymorphism of the land snail Cepaea nemoralis. Traditionally, the view is that the ground colour of the shell is one of a few major colour classes, either yellow, pink or brown, but in practise it is frequently difficult to distinguish the colours, and define different shades of the same colour. To understand whether colour variation is in reality continuous, and to investigate how the variation may be perceived by an avian predator, we applied psychophysical models of colour vision to shell reflectance measures. We found that both achromatic and chromatic variation are indiscrete in Cepaea nemoralis, being continuously distributed over many perceptual units. Nonetheless, clustering analysis based on the density of the distribution did reveal three groups, roughly corresponding to human-perceived yellow, pink and brown shells. We also found large-scale geographic variation in the frequency of these groups across Europe, and some covariance between shell colour and banding patterns. Although further studies are necessary, the observation of continuous variation in colour is intriguing because the traditional theory is that the underlying supergene that determines colour has evolved to prevent phenotypes from "dissolving" into continuous trait distributions. The findings thus have significance for understanding the Cepaea polymorphism, and the nature of the selection that acts upon it, as well as more generally highlighting the need to measure colour objectively in other systems.
生物学家长期以来一直试图描述和命名构成陆地蜗牛 Cepaea nemoralis 壳多态性的不同表型。传统上，观点认为壳的底色是少数几种主要颜色类别之一，要么是黄色、粉色或棕色，但实际上，颜色往往难以区分，并且难以定义同一颜色的不同色调。为了了解颜色变化是否实际上是连续的，并研究这种变化可能如何被鸟类捕食者感知，我们应用颜色视觉的心理物理学模型来测量壳的反射率。我们发现 Cepaea nemoralis 中的非彩色和彩色变化都是不连续的，而是在许多感知单位中连续分布。尽管如此，基于分布密度的聚类分析确实揭示了三个组，大致对应于人类感知的黄色、粉色和棕色壳。我们还发现，这些组在整个欧洲的频率存在大规模的地理变异，并且壳颜色和带图案之间存在一些协方差。尽管还需要进一步的研究，但对颜色连续变化的观察是有趣的，因为传统理论认为决定颜色的基础超基因已经进化到防止表型“溶解”到连续的特征分布中。因此，这些发现对理解 Cepaea 多态性以及对其起作用的选择性质具有重要意义，并且更普遍地强调了在其他系统中客观测量颜色的必要性。
