Quantifying colour patterns on the black carapace of the fiddler crab Uca capricornis

Fiddler crabs are often spectacularly coloured and capable of dramatic colour changes. While the adaptive significance of variation resulting from short- or long-term colour changes is generally well known, the phenotypic diversity in colour pattern between individuals is often neglected. To fully understand the development and function of colour pattern variation, it is necessary to first describe its morphological basis and the naturally occurring diversity. - NB Colour pattern refers to the configuration of any coloured areas on the black carapace, regardless of their spectral composition. \n\nDuring this experiment 276 fiddler crabs of the species Uca capricornis were photographed - 117 females and 159 males. Using these pictures and a host of software programs, images were constructed that illustrate the probable colour patterns of various groups of crabs, including males and females in general, and males and females with various size classes; 18mm (no photographed females were >18mm). These images are the equivalent of an average crab's colour pattern. \n\nTo more clearly illustrate the variation in colour pattern between the groups, similar images were constructed using the standard deviation of crabs coloured at each coordinate (1mm x 1mm square).

招潮蟹（Fiddler crab）通常体色艳丽，且可发生剧烈的体色变化。尽管学界已普遍明确短期或长期体色变化所带来的体色差异的适应意义，但个体间体色模式的表型多样性却常被忽视。为全面解析体色模式变异的发生机制与功能，首先需阐明其形态学基础与自然存在的多样性。——注：体色模式指黑色头胸甲上所有有色区域的排布形式，不考虑其光谱组成。

本实验共拍摄了276头角眼招潮蟹（Uca capricornis）标本，其中雌性117头，雄性159头。研究人员基于这批照片与多款软件工具，构建了可展示不同类群招潮蟹代表性体色模式的图像，涵盖通用雌雄个体，以及不同体长组的雌雄个体；体长分组包含18mm组（本次拍摄的雌性个体体长均不超过18mm）。此类图像代表对应类群招潮蟹的平均体色模式。

为更清晰地呈现不同类群间的体色模式差异，研究人员以每1mm×1mm坐标方格内个体体色的标准差为依据，构建了同类对比图像。