Poison frogs across Central and South America display some of the most stunning colors in the animal kingdom. Some species are cobalt or indigo; others are yellow, golden, strawberry pink, or bright stop-sign red and striped down the back.
While these hues are splendid to marvel at, the color actually serves as a warning sign to potential predators: Eat me and I will poison you.
The way that these creatures and other animals evolved to be just colorful enough to signal their toxic defense — but not so colorful that they become vulnerable to predators — has long been a grey area for scientists.
Now a new study published in the journal Science might explain the phenomenon.
“We know that evolution can explain the traits that we see, but learning the mechanics of how we get from one place to another really gives a deeper understanding of nature,” says Karl Loeffler-Henry, a researcher at Carleton University and one of the lead authors of this study.
A Common Survival Tactic
Being brilliantly colorful to signal to predators that you’re toxic, deadly or simply “not a snack” is a phenomenon called aposematism.
It is widespread among gaudy amphibians, reptiles, insects and other critters.
This characteristic has also evolved independently across various lineages of animals with chemical defenses. So, it’s clearly a handy party trick in the annals of evolutionary survival.
But evolutionary scientists have long puzzled over how animals could evolve to be so scintillating without tipping themselves off to predators in the first place.
Paradox of the Vulnerable Prey
Evolution happens when a random genetic mutation makes certain animals within a species more likely to survive and reproduce.
Presumably, a variation like this bright color pattern would have posed a dilemma for the first individuals where the mutation occurred.
That’s because, initially, predators would not have known that bright colors signal toxicity, and therefore would have eaten — and then become ill — these easily-spotted few members of a species with the colorful mutation.
In theory, this should make it virtually impossible for the aposematic pioneers to pass on their genes to their offspring, allowing for the mutation to take hold in the population.
“You have this kind of paradoxical catch-22, wherein the prey needs to be sampled by the predator in order for predators to be educated about associating the color with the toxic defense,” says Loeffler-Henry. “But when predators sample those individuals, it’s necessarily lethal to the individual.”
Data From 1,100 Colorful Species
To get to the bottom of this paradox, Loeffler-Henry’s team pored over data from the family trees of 1,100 species of frogs, newts and salamanders, and categorized them into one of five groups.
On one end of the spectrum are the creatures with raging blues, yellows and reds that differentiate them from the rest. This group, the conspicuous bunch, includes icons like the various different colored poison dart frogs.
On the other end of the spectrum: amphibians that blend in perfectly with their surroundings.
Painted in muted greens, browns and grays, they camouflage into their habitats in a cryptic way. Think of the Vietnamese mossy frog (Theloderma corticale), which looks like it’s actually covered in moss.
Between these poles, the scientists place amphibian species with camouflaged tops and colorful bottoms in various degrees — some with bright bellies, others with colorful under-limbs, some with a little of both. These tend to display their dramatic halves only when trying to defend themselves from predators.
The Hong Kong warty newt (Paramesotriton hongkongensis) belongs to this category because it’s brown on the top and spotted orange on the bottom. So does the black-and-yellow walking toad (Melanophryniscus stelzneri), which is black on its back and mottled bright red on its belly.
Modeling the Different Possibilities
Loeffler-Henry’s team used nine different computer models to test the potential evolutionary routes that frogs, newts and salamanders in the conspicuous aposematic group might have taken to evolve this way.
In the end, the researchers realized that they all kind of followed a similar pattern.
The aposematic amphibians almost always evolve from species in the middle of that spectrum, those whose colors are shrouded unless in danger.
“We found that the transition from camouflage to aposematism is seldom direct,” says Loeffler-Henry.
Rather, the intermediary hidden-signals phase seems to have facilitated the transition in most instances.
Different Environmental Advantages
Of course, this doesn’t mean all species are going to evolve to be super toxic and super colorful.
Depending on the environment, there are unique benefits that come with being either a camouflaged species or one which uses hidden signals — or one that is fully bright and aposematic.
Many toxic amphibians are still camouflaging too, Loeffler-Henry points out.
Read More: 6 Animals With Unusual Evolutionary Traits
There have also been other theories proposed to resolve this paradox of the brightly colored amphibians.
One of them proposes that predators might be initially wary to attack novel prey.
Another suggests that predators might be able to share with each other, through social learning, the knowledge that bright colors signal danger.
But this new theory presents a mechanism that is likely to play a role in the evolution of anti-predator defense in various prey groups and a wide range of different predators, says Alice Exnerová, a zoology professor at Charles University in Prague, who was not involved in the new study.
Application Beyond Amphibians
“It is well possible that this process [of having hidden colors] might have played an important role in the evolution of warning coloration in other animal groups besides the amphibians,” says Exnerová.
For example, there are fish, moths, mantids and grasshoppers with hidden warning color patterns that place them in the middle of the conspicuous-camouflage spectrum.
To test how widespread this evolutionary trick is among the animal kingdom, more research looking into animals like these could reveal a rainbow of results.