Why don't all poison dart frogs look the same?
(Image credit: Flickr user William Wan)
Nothing says "STAY AWAY!" to a predator like a tasty-looking creature that's a little too flashy. Bright colors and crazy patterns are nature's skull and crossbones, a warning to the carnivorous to look elsewhere for meals. Toxic animals usually have uniform markings: Each member of a species looks the same. Monarch butterflies bear the same patterns; puffer fish all puff up in the same way. But there's one animal that ignores this advice completely: the poison dart frog. These deadly amphibians have developed endless combinations of shades and markings, making it a challenge for hungry birds and snakes to keep track of their patterns. If the idea of being visibly toxic is to be as obvious as possible, why would a single species of frog maintain such an extensive wardrobe? That's the question that had Mathieu Chouteau sweating in the Peruvian Amazon as fastened 1,800 clay frogs to rainforest leaves.
(Image credit: Flickr user MoleSon²)
Back in 2009, Chouteau, a biologist from the University of Montreal, became obsessed with this evolutionary puzzle. "For the longest time, I've been fascinated by the phenomenon of local adaptation," he says. But because the varieties of poison dart frog patterns are so many and, more importantly, occur so geographically close to one another, they struck Chouteau as particularly odd. He wondered whether different types of local predators were somehow responsible for the variations.
(Image credit: Flickr user Geoff Gallice)
With the help of a patient girlfriend, fellow biologist Melanie McClure, he was able to test his theory. For an entire month, Chouteau and McClure spent four to six hours a day molding and hand painting nearly 2,000 clay frogs. Before long, it looked like an invasive species had taken over the couple's home. In his experiment, Chouteau focused on two patterns. Some of his frogs were painted to look like a group from the Peruvian highlands: black and splashed with bright green blotches. The other mimicked the pattern on a group of lowland frogs living six miles away: black with yellow stripes.
(Image credit: Flickr user Geoff Gallice)
In the field, the variety is even more astonishing. Some poison dart frogs are striped with bands of black and gold, like the business end of a bumblebee. Some are spotted. Some are speckled. Some are neon yellow all over. But all of them are easy to spot, glittering like gems on leaves and branches. They're also dangerous. Each frog is packed with toxic alkaloids that wreak havoc on cell communication and lead to fibrillation, arrhythmia, cardiac failure, or death. A few varieties are so poisonous that indigenous tribesmen use them to give their blowgun darts extra stopping power.
As soon as the paint on Chouteau's models had dried, he packed up his decoy frogs and headed to the Amazon for the next painstaking task: Using toothpicks, he pinned the clay hors d'ouvres to low-hanging leaves in both highland and lowland locations, It took days.
(Image credit: Flickr user Jacob Kirkland)
When Chouteau returned to check on his frogs, he found that some of the models had been marred by beaks, talons, and fangs. He continued to check in for the next three days. In that time, some frogs had been ripped clean in half or disappeared altogether. But many remained intact. It all depended on which frogs were in which locations. In each zone, the predators -mostly birds, snakes, and spiders- had gone after the foreign-looking frogs almost four times more than the ones that sported familiar patterns. The trend became clear: Local predators steered clear of local frogs, but they were willing to taste the ones they didn't recognize. Chouteau's work showed that the frog's color variety wasn't some great evolutionary plan. The frogs that local predators learned to avoid -the ones that ended up populating and flourishing in a particular area- weren't smarter, faster, or better-looking. They were just lucky enough to be wearing the right spots in the right spot.
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