How did animals develop warning colours?

Many amphibians show their potential predators in bright red, orange or yellow: I’m poisonous, don’t eat me! But how could such warning colors have evolved evolutionarily? Why were these notable individuals not killed directly by predators who did not yet know the warning message of the colors? A study is now shedding light on possible mechanisms. Thus, warning colors may have evolved secretly at first, only appearing when an otherwise camouflaged animal displayed them on purpose. Only when the predators recognized the colors as a deterrent were individuals in permanent warning clothing able to assert themselves.

In the course of evolution, animals have evolved a variety of strategies to protect themselves from predators. Some almost blend in with their surroundings, imitating the color of the earth, leaves, or tree bark. Others, on the other hand, can be seen from afar with their attractive patterns and bright colours. But predators intuitively know this means a warning: the animals in question may be poisonous, defensive, or at least inedible. However, how the warning coloration strategy, also known as aposematism, could have developed evolutionarily is considered a scientific paradox. At a time when the meaning of color was not yet understood by predators, the first individuals to evolve flashy colors through random mutation were especially at risk of being eaten. Thus, the trait cannot assert itself evolutionarily.

Clarifying the paradox

A team led by Carl Loeffler Henry of Carleton University in Ottawa, Canada, found a plausible solution to this paradox. “Our study underscores the importance of hidden color cues in the evolutionary processes that lead to diverse coloration in amphibians to deter predators,” the researchers said. Whereas previous studies on the evolution of warning colorations typically divided analyzed species into only two groups—camouflage or warning colors—Loeffler-Henry and colleagues also looked at the variants between them.

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“Some species are camouflaged when at rest, but have bright colored markings on hidden parts of the body that only appear in certain situations, such as when fleeing or when they are in a defensive position,” explains the research team. For example, many frogs are inconspicuously colored on the upper side, while their abdomen has all or part of the warning colouring. “These flexible signaling strategies could represent intermediate stages, and thus play a central role in the evolutionary processes that produce different defense mechanisms against predators.”

Intermediate development

To test this hypothesis, Loeffler-Henry and his team conducted phylogenetic analyzes of a total of more than 1,400 species of amphibians. They divided these into five groups: in addition to species that are camouflaged and conspicuously coloured, they also considered those whose abdomens had warning colours, in whole or in part, and species that produced camouflaged and conspicuous individuals. They also have information on the toxicity of 315 species, so they can also include the extent to which warning colors actually indicate danger and in cases where they are just a hoax. Using nine different evolutionary models, the research team calculated the most likely pathway through which sepsis evolved and the role of toxicity in that.

The result: “Our analyzes show that the evolutionary transition from camouflage to valence does not usually occur directly, but involves an intermediate stage, namely the camouflaged species that voluntarily exhibit conspicuous colouration,” say the researchers. About 91 percent of species with facultative warning coloration have chemical defenses. This indicates that their warning coloration is an honest signal of their defense rather than a hoax. Predators thus learn to interpret bright colors as an indication of danger, even before individuals who have abandoned their camouflage entirely in favor of warning colors prevail. Because brightly colored individuals are eaten less often later on, selection pressure can develop that leads to completion. full.

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Be aware of hidden signs

“Macroevolutionary studies of animal coloration should take into account these subtle and underestimated cues scattered throughout the animal kingdom to improve our understanding of the evolution of predator defenses,” the authors wrote. “Indeed, in many groups of animals, such as snakes, fish, and a variety of arthropods, there are species that carry clear signals in hidden locations. We therefore encourage follow-up studies in other taxa to assess the generality of the intermediate step hypothesis as a route to poisoning.”

Source: Karl Loeffler-Henry (Carleton University, Ottawa, Canada) et al., Science, Available Here. doi: 10.1126/science.ade5156

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