Thistle-down velvet ants in the Desert Mimicry Ring and the evolution of white coloration: Müllerian mimicry, camouflage, and thermal ecology

Adaptive coloration among animals is one of the most recognizable outcomes of natural selection. Here we investigate evolutionary drivers of white coloration in velvet ants (Hymenoptera: Mutillidae), which has previously been considered camouflage with the fruit of creosote bush. Our analyses indicate instead that velvet ants evolved white coloration millions of years before creosote bush was widespread in North America’s hot deserts. Furthermore, velvet ants and the creosote fruit exhibit different spectral reflectance patterns, which appear distinct to potential insectivorous predators. While the white coloration in velvet ants likely did not evolve as camouflage, we find that white-colored species remain cooler than their red/orange relatives, and therefore we infer the white coloration likely evolved in response to Neogene desertification. This study shows the importance of cross-disciplinary investigation and the importance of testing multiple hypotheses when investigating evolutionary drivers of adaptive coloration.