We have a habit of seeing nature in snapshots. We marvel at the adaptation of a species–see Ed Yong today on the maneuverability of cheetahs, for example–and don’t give much though about how it came to be. These snapshots can become downright confusing when we survey the diversity of many different species. Each species may have a radically different solution to the same problem. If one solution is so impressive, how could another one evolve, too?
The cure for this puzzlement is to get away from the snapshots. A species is a blurry, speckled thing. It’s made up of populations spread across a range, and each population is made up of many individuals, each with its own somewhat distinct set of genes. Those genes flow around the range, from individual to individual, mixed into new combinations, some spreading far and wide, some vanishing after a generation.
The picture I’ve reproduced above is a wonderful epitome of that blurriness. It shows frogs that live in Costa Rica at various spots along the Pacific Coast. Some frogs, like the green one at the northern end of the coast, develop colors that help them fade into surrounding vegetation. It’s an impressive way to hide from predators, matching one’s skin to the color of plants.
Other frogs, like the bright red one at the southern end of this picture, are not shy at all. They use brilliant colors, rather than masking ones, in order to ward of predators. These frogs produce poisons in their skin, which can sicken or kill an attacker. By developing a bright color that pops out from the surroundings, frogs can make it easy for birds and other predators to learn to link their appearance to a nasty experience. As a result, the predators stay away.
Same problem–two solutions. Which brings up the question, why would some frogs hide from predators while others tried to get their attention?
And here’s what’s so fascinating about this picture. Those frogs you see are all part of the same species, the granular poison frog, Oophaga granulifera.
In the journal Evolution, Beatriz Willink of the University of Costa Rica and her colleagues take a look at this species’s spectrum from camo green to strawberry red. The frogs don’t just vary in color. They also vary in the way they behave. The green frogs are shy compared to the red ones. Willink and her colleagues found that the green males sang less than half the time that the red male frogs did, for example. The green frogs also spent less time looking for food. In skin and brain alike, the green frogs survive by hiding, while the red frogs fend off death by showing off.
The frogs freely mate with their neighbors, which means that genes from one end of the species range can flow towards the other. And yet those flowing genes have not smeared the species into a single kind of frog. Across just 25 miles or so, they can span the distance from camouflage to conspicuousness.
As effective as those two strategies may be, Willink and her colleagues found that in between the extremes, the frogs were intermediate. Some were yellowish-green, while others were orange. But the intermediates didn’t smoothly grade from one end of the spectrum to the other. They had fascinating jumbles of traits.
There are two ways for frogs to contrast with their surroundings, for example: in brightness and in color. The intermediate frogs had a low brightness contrast, like the green frogs, but a high color contrast, like the red frogs. And instead of having an intermediate level of boldness, they were almost as bold as the red frogs, too.
All the frogs in this species have to cope with predators, and they’re evolving different ways to do so–not just through camouflage or conspicuousness, but in combinations of the two. Willink and her colleagues argue that the low brightness contrast of intermediate frogs is a good way to avoid notice from birds, because their brains seize on changing brightness contrast to notice prey. If that fails, and a bird comes closer to investigate, a frog can still boost its odds of surviving with high color contrast, which is how birds learn to stay away from poisonous prey.
For some reason scientists have yet to work out, the balance of strategies that works best is different at the northern and southern ends of the frog’s range. Ian Wang of the University of California, Davis, has found that the yellow and green populations of frogs evolved from the red one. In other words, they abandoned the showy colors of their ancestors. It’s possible that geography explains why they did so. Northern frogs may face a bigger threat from snakes, for example, which rely on smell instead of vision to recognize dangerous prey.
Wang also found that the green frogs are actually more toxic than the red ones. Rather than waste effort on showy red pigments, perhaps the northern frogs evolved to put their energies into making poison.
Whatever the answer turns out to be, this picture already makes one thing clear: there’s more than one way to be a granular poison frog.
Go Further
Animals
- Octopuses have a lot of secrets. Can you guess 8 of them?
- Animals
- Feature
Octopuses have a lot of secrets. Can you guess 8 of them? - This biologist and her rescue dog help protect bears in the AndesThis biologist and her rescue dog help protect bears in the Andes
- An octopus invited this writer into her tank—and her secret worldAn octopus invited this writer into her tank—and her secret world
- Peace-loving bonobos are more aggressive than we thoughtPeace-loving bonobos are more aggressive than we thought
Environment
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
- Food systems: supporting the triangle of food security, Video Story
- Paid Content
Food systems: supporting the triangle of food security - Will we ever solve the mystery of the Mima mounds?Will we ever solve the mystery of the Mima mounds?
- Are synthetic diamonds really better for the planet?Are synthetic diamonds really better for the planet?
- This year's cherry blossom peak bloom was a warning signThis year's cherry blossom peak bloom was a warning sign
History & Culture
- Strange clues in a Maya temple reveal a fiery political dramaStrange clues in a Maya temple reveal a fiery political drama
- How technology is revealing secrets in these ancient scrollsHow technology is revealing secrets in these ancient scrolls
- Pilgrimages aren’t just spiritual anymore. They’re a workout.Pilgrimages aren’t just spiritual anymore. They’re a workout.
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- This ancient cure was just revived in a lab. Does it work?This ancient cure was just revived in a lab. Does it work?
- See how ancient Indigenous artists left their markSee how ancient Indigenous artists left their mark
Science
- Jupiter’s volcanic moon Io has been erupting for billions of yearsJupiter’s volcanic moon Io has been erupting for billions of years
- This 80-foot-long sea monster was the killer whale of its timeThis 80-foot-long sea monster was the killer whale of its time
- Every 80 years, this star appears in the sky—and it’s almost timeEvery 80 years, this star appears in the sky—and it’s almost time
- How do you create your own ‘Blue Zone’? Here are 6 tipsHow do you create your own ‘Blue Zone’? Here are 6 tips
- Why outdoor adventure is important for women as they ageWhy outdoor adventure is important for women as they age
Travel
- This royal city lies in the shadow of Kuala LumpurThis royal city lies in the shadow of Kuala Lumpur
- This author tells the story of crypto-trading Mongolian nomadsThis author tells the story of crypto-trading Mongolian nomads
- Slow-roasted meats and fluffy dumplings in the Czech capitalSlow-roasted meats and fluffy dumplings in the Czech capital