The Colourful World of Platyrrhine Monkeys: Skin Colour Variation and Its Potential Role in Communication

Abstract

Understanding the evolution of human communication has been a longstanding goal of anthropologists and has spurred many lines of research. Studying our closest living relatives, the non-human primates (NHPs), provides an opportunity to better understand human communication, by placing it in a comparative context. Among NHPs, use of colour signals is common and widely distributed across the Order. Catarrhines have trichromatic colour vision and exposed skin colouration plays an important role in their interactions. In platyrrhines, exposed skin is less common, but some genera have widely exposed body regions, suggesting that skin colouration might also be used for communication. Intriguingly, platyrrhines have polymorphic colour vision, in which some individuals are dichromats while others are trichromats. This polymorphism may affect signal perception by conspecifics and shape some aspects of communication. However, we currently lack studies measuring colour (hue, saturation, chroma) variation in their skin. In this thesis, I provide several studies that seek to explore the potential for colour signals in platyrrhines. I provide the first analysis of the distribution and evolution of facial skin exposure and colour in platyrrhines in Chapter 2. I then report in Chapter 3 variation in facial skin colour of golden lion tamarins (Leontopithecus rosalia) in the context of breeding status, reproductive condition, and age. In Chapter 4, I investigate if female genital skin colour of two species of wild tamarins [saddleback (Leontocebus weddelli) and emperor tamarins (Saguinus imperator)] vary between developmental classes. Finally, I study the hypertrophied and pendulous clitoris of female black-handed spider monkeys (Ateles geoffroyi) and investigate if its colour and shape varies within and between individuals. My results suggest that among platyrrhines there is extensive variation in skin exposure and colouration and that colour seems to be linked to breeding status, reproductive condition and age in some species, and colour variation occurs within and between individuals. These results show potential for convergence in some functions of bare-skin signaling in catarrhine primates. My Doctoral Thesis makes contributions to the understanding of primate communication by adding new comparative data to illuminate the selective pressures shaping the sensory and communication systems across our order.