Histological structure of the facial skin in the bald uakari (Cacajao calvus), compared to other non-red Neotropical primates

In social species, such as primates, facial appearances transmit a variety of social signals. Although it is suggested that the intense red colour of the face of the bald uakari monkey might be an indicator of health, this hypothesis still has not been verified. This study describes the histological structure of the skin of the face in the bald uakari, compared with other non-red neotropical primates, to better understand the maintenance of its colour. The facial skin of the bald uakari monkey is characterized by a thinner epidermis, absence of melanin pigments and a high density of vascular capillaries that spread below the epidermis. These vascular capillaries are larger and more tortuous than in other neotropical primates. The skin of the face of the bald uakari monkey allows a direct external assessment of haematological status, suggesting that the colour of the face would be an honest indicator of health, but could also signal sexual or behavioural states.

在群居物种中，例如灵长类动物，面部特征传递着各种社会信号。尽管有观点认为无毛卷尾猴面部鲜明的红色可能标志着健康状态，但这一假设尚未得到证实。本研究旨在描述无毛卷尾猴面部皮肤的病理学结构，并将其与其他非红色新热带地区灵长类动物进行对比，以更深入地理解其颜色的维持机制。无毛卷尾猴的面部皮肤以表皮较薄、缺乏黑色素色素以及富含血管毛细血管为特征，这些血管毛细血管的分布延伸至表皮之下。相较于其他新热带地区灵长类动物，这些血管毛细血管更为粗大和扭曲。无毛卷尾猴的面部皮肤允许直接对外部血液状态进行评估，暗示面部颜色可能是健康的真实指示器，但也可能传递性或行为状态的信息。