Characteristics of sun bear chest marks and their patterns of individual variation

Here I survey, collate and synthesize contrasting coloration in 5000 species of terrestrial mammals focusing on black and white pelage. After briefly reviewing alternative functional hypotheses for coloration in mammals, I examine nine colour patterns and combinations on different areas of the body and for each mammalian taxon to try to identify the most likely evolutionary drivers of contrasting coloration. Aposematism and perhaps conspecific signalling are the most consistent explanations for black and white pelage in mammals; background matching may explain white pelage. Evidence for contrasting coloration is being involved in crypsis through pattern blending, disruptive coloration or serving other functions, such as signalling dominance, lures, reducing eye glare or in temperature regulation has barely moved beyond anecdotal stages of investigation. Sexual dichromatism is limited in this taxon and its basis is unclear. Astonishingly, the functional significance of pelage coloration in most large charismatic black and white mammals that were new to science 150 years ago still remains a mystery. Show more

Colour patterns (e.g. irregular, spotted or barred forms) are widespread in the animal kingdom, yet their potential role as signals of quality has been mostly neglected. However, a review of the published literature reveals that pattern itself (irrespective of its size or colour intensity) is a promising signal of individual quality across species of many different taxa. We propose at least four main pathways whereby patterns may reliably reflect individual quality: (i) as conventional signals of status, (ii) as indices of developmental homeostasis, (iii) by amplifying cues of somatic integrity and (iv) by amplifying individual investment in maintenance activities. Methodological constraints have traditionally hampered research on the signalling potential of colour patterns. To overcome this, we report a series of tools (e.g. colour adjacency and pattern regularity analyses, Fourier and granularity approaches, fractal geometry, geometric morphometrics) that allow objective quantification of pattern variability. We discuss how information provided by these methods should consider the visual system of the model species and behavioural responses to pattern metrics, in order to allow biologically meaningful conclusions. Finally, we propose future challenges in this research area that will require a multidisciplinary approach, bringing together inputs from genetics, physiology, behavioural ecology and evolutionary-developmental biology. Show more