How poisonous amphibians evolve bright colours to warn predators off

The mystery of how animals evolve bright colors to warn predators of toxic or disgusting tastes seems to have been solved, at least for amphibians.

Some animals have conspicuous colors or patterns to warn predators that they taste awful or are poisonous. This approach protects most of them because they stop attacking the .

But when mutations spread throughout a population, evolution occurs. It is difficult to understand why mutations that make animals brightly colored are beneficial and widespread. Because the first few animals with that trait are much more likely to be caught by predators.

“There’s this paradoxical catch 22: A predator needs to sample an individual to know that bright colors are associated with chemical defense, but sampling the individual kills the individual.” Therefore, we can prevent the spread of its adaptation,” says Karl Loeffler-Henry of Carleton University in Ottawa, Canada.

Animals with hard shells, such as beetles, are more likely to survive an attack even if a predator spits them out in disgust, and this may explain how warning colors evolve in insects. However, this is not the case for soft-bodied amphibians.

However, some amphibians, such as toads, have brightly colored body parts that are normally hidden. Such animals remain camouflaged most of the time, but may exhibit bright colors when threatened or fleeing predators.

Loeffler-Henry and his colleagues wondered if this could explain the paradox. Animals that are normally masked in color are less vulnerable to predators and can spread in populations. As the trait spread, predators learned its meaning, paving the way for the evolution of animals with bright colors on prominent body parts.

To test this idea, the researchers analyzed genealogies of 1,100 species of frogs, newts and salamanders. By comparing living animals, they determined whether their direct ancestors had prominent colors, normally hidden colors, or no obvious colors at all. . They found that amphibians with prominent colors almost always evolved from amphibians whose colors were normally hidden.

“For amphibians, this seems to be the main route,” says Loeffler-Henry. “I think it solves the amphibian paradox.”

“This study provides strong evidence,” said David Kikuchi of Oregon State University. “This will really change the scope of the process we think of when considering the evolution of warning signals.”

Kikuchi says the most compelling finding is that usually hidden signals often develop into prominent ones, but rarely the other way around. But confirming these ideas will require studying how predators respond to signals that are normally hidden, he says.

Loeffler-Henry also hopes that studies like his will be done in groups such as fish, snakes and insects to see if this evolutionary process is general beyond amphibians.