Evolution of bright colours in animals: worlds of prohibition and oblivion.

Because the ability to hide in plain sight provides a major selective advantage to both prey and predator species, the emergence of the striking colouration of some animal species (such as many coral reef fish) represents an evolutionary conundrum that remains unsolved to date. Here I propose a framework by which conspicuous colours can emerge when the selective pressures for camouflage are relaxed (1) because camouflage is not essential under specific prey/predator conditions or (2) due to the impossibility of reducing the signal-to-background noise in the environment. The first case is found among non-predator-species that possess effective defences against predators (hence a "Carefree World"), such as the strong macaws' beaks and the flight abilities of hummingbirds. The second case is found in diurnal mobile fish of coral reef communities, which swim in clear waters against highly contrasting and unpredictable background (hence an "Hyper-Visible World"). In those contexts the selective pressures that usually come secondary to camouflage (such as sexual, warning, species recognition or territorial display) are free to drive the evolution of brilliant and diverse colouration. This theoretical framework can also be useful for studying the conditions that allow for conspicuousness in other sensory contexts (acoustic, chemical, electrical, etc.).