Supplementary Material for: Spectrocolourimetry Visualized Differences in Sexual Skin Colouration in Macaques

The females of some catarrhines develop conspicuous sexual skin transformations in their hind limbs. Among macaques (one of the radiated and adapted catarrhine groups with diversified sexual skin transformations), differences in sexual skin colouration between the Japanese macaque Macaca fuscata and the rhesus macaque M. mulatta have not been quantitatively analysed. In this study, the sexual skin colouration of these macaques was spectrocolourimetrically measured in the non-mating season (NMS) and the mating season (MS) and represented in a CIELAB space with the variables L*, a* and b*. The variables L*, a* and b* represent positions on the light-dark, red/magenta-green, and yellow-blue axes, respectively. In the Japanese macaques the average ± SD of L*, a* and b* was 53.61 ± 3.31, 11.51 ± 4.57 and 6.66 ± 2.25 in the NMS and 46.60 ± 2.78, 19.97 ± 2.99 and 8.80 ± 1.34 in the MS, respectively, while in the rhesus macaques the average ± SD of L*, a* and b* was 60.09 ± 3.96, 5.99 ± 4.59 and 5.83 ± 2.37 in the NMS and 52.70 ± 6.54, 13.62 ± 6.86 and 8.07 ± 1.43 in the MS, respectively. The sexual skin of the Japanese macaques was consistently much redder (larger a*) and darker (smaller L*) than that of the rhesus macaques. The smaller L* suggested a greater dermal melanin content in the Japanese macaques. These closely related macaque species have similar but distinct sexual skin colourations. Spectrocolourimetry is thus useful to suggest the histophysiological background of the colouration.

部分狭鼻猴类（catarrhines）的雌性个体在后肢会出现显著的性皮肤形态变化。猕猴属（macaques）作为辐射演化且适应性强的狭鼻猴类类群之一，其性皮肤形态呈现多样化特征，但目前针对日本猕猴（Macaca fuscata）与恒河猴（M. mulatta）之间的性皮肤色彩差异，尚未开展定量分析。本研究采用分光比色法（spectrocolourimetry），对这两种猕猴在非交配季（NMS）与交配季（MS）的性皮肤色彩进行检测，并以CIELAB色彩空间的L*、a*、b*三个参数进行表征。其中L*、a*、b*分别对应明暗轴、红/品红-绿轴以及黄-蓝轴上的色彩坐标。日本猕猴在非交配季的L*、a*、b*均值±标准差（SD）分别为53.61±3.31、11.51±4.57、6.66±2.25，交配季则分别为46.60±2.78、19.97±2.99、8.80±1.34；恒河猴在非交配季的L*、a*、b*均值±标准差分别为60.09±3.96、5.99±4.59、5.83±2.37，交配季则分别为52.70±6.54、13.62±6.86、8.07±1.43。日本猕猴的性皮肤始终比恒河猴更偏红色（a*值更高）且色调更深（L*值更低）。L*值更低提示日本猕猴的皮肤黑色素含量更高。这两种亲缘关系紧密的猕猴，其性皮肤色彩既存在共性，又具有显著差异。因此，分光比色法可为揭示性皮肤色彩的组织生理学背景提供有效研究手段。