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How did warning coloration evolve in animals?

Some animal species use bright color patterns to keep predators away – a phenomenon known as “aposematism.” Scientists have long pondered how aposematic animals can survive long enough for this warning signal coloration to evolve before predators learn to avoid them. 

Now, a team of scientists from Carleton University in Canada and Seoul National University in South Korea has found that, during evolution, aposematism emerged through intermediate steps. Initially, coloration was only visible when an animal was fleeing or intentionally displaying color patterns that are normally hidden.

Evolutionary adaptations to avoid being tracked by predators have led to a considerable variation in the diversity of animal color patterns. While some species developed camouflage coloration, enabling them to blend into the background in order to avoid detection, others evolved to exhibit bright colors as conspicuous warning signals that advertise defense mechanisms such as venom, toxicity, or aggression.

The researchers performed a large-scale phylogenetic analysis of over 1,400 amphibian species with known warning coloration along nine different evolutionary models. They discovered that the evolutionary transition from camouflage coloration to aposematism was rarely direct and most likely emerged through a series of intermediary steps in which warning coloration was first hidden and only selectively visible.

According to the scientists, predators encountering such hidden warning signals probably continued to treat permanently aposematic mutants with caution, a phenomenon providing selective pressure for warning coloration to become a permanent adaptation. 

“Macroevolutionary studies on animal coloration should take into account these underappreciated hidden signals, which are both common and widespread across the animal kingdom, to advance our understanding of the evolution of antipredator defenses,” wrote the researchers.

“Indeed, many animal taxa such as snakes, fishes, and a variety of arthropods include species that are cryptic, aposematic, and have hidden conspicuous signals. We therefore encourage follow-up studies in other taxa to evaluate the generality of the steppingstone hypothesis as a route to aposematism.”

The study is published in the journal Science.

By Andrei Ionescu, Staff Writer

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