Red coloration and the evolution of aposematism in arboreal sciurids

An animal's coloration is associated with a variety of processes and is therefore subjected to multiple selective pressures. Mammals, especially, are typically inconspicuously colored, or cryptic, to avoid detection by predators. Alternatively, an animal may use conspicuous coloration to advertise the presence of an anti-predator defense. The association between signal and defense is called aposematism. Conspicuous black and white coloration has recently been associated with a range of defenses in mammals, including body size (Howell et al. 2021), however red coloration as a potentially aposematic signal has yet to be investigated in mammals. Squirrels, like most mammals, are unable to perceive red for use as a social signal. Here we use a comparative framework to test whether redness could be a means of background matching, serve a thermoregulatory function or be an honest warning of anti-predator defenses across a global distribution of tree squirrels which vary in size from 16g to 2....