Abstract
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.).
Highlights
The ability to hide in plain sight is a major selective pressure for both prey and predatory species[1,2]
Traits that increase an individual’s capability to camouflage with its surrounding environment have likely been under strong selection pressure since vision emerged, having guided, to a great extent, the evolution of visual displays in the animal world. It is in this context that the eyecatching colouration of fish inhabiting coral reefs and other tropical bodies of water has puzzled scientists since the formulation of the natural selection theory[3,4,5,6,7,8,9,10,11]
Alfred Russel Wallace, co-proponent of the natural selection theory, was the first to put forth a hypothesis that attributed camouflage properties for those bright colour patterns, whereby “brilliantly-coloured fishes from warm seas are many of them well concealed when surrounded by the brilliant sea-weeds, corals, sea-anemones, and other marine animals, which make the sea-bottom sometimes resemble a fantastic flower-garden”[3]
Summary
The ability to hide in plain sight is a major selective pressure for both prey and predatory species[1,2]. One of the main selective pressures on colour vision of predators and prey is directed to enhance the perception of contrast between object and background[6,20] and, in order to cancel this out, the aim of camouflage is to induce exactly the opposite In coral reefs, this signal/noise ratio cannot be reduced by diurnal mobile fish under virtually whatever colour pattern that could be chosen to cover their body. On the other hand, a fish spends most of its time in one location, natural selection can favour pigmentation and morphologies that match that predictable substrate (be it a coral species, type of rock or sand colouration) This “Hyper-visible world” hypothesis presents a specific and falsifiable (sensu Popper23) prediction: other traits being equal, roaming fish with any degree of visual prominence will endure equivalent predatory pressure (or success) in coral reefs, but not when swimming against a predictable and homogenous background. Grant information The author declares that no grants were involved in supporting this work
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