How the Tree Frog Has Redefined Our View of Biology

The world’s most charismatic amphibian is upending the conventional wisdom about evolution

A beloved symbol of biodiversity, the red-eyed tree frog, shown here in Panama, has evolved a flexible strategy for survival. (Christian Ziegler)
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They walk down a road into a nursery for native plants, cross a ditch on a footbridge and arrive at Experimental Pond. It was built of concrete to specifications provided by Warkentin and Stan Rand, a revered frog researcher at STRI, who died in 2005.

On the pond’s far side is the group’s research area, bounded by a ditch on one side and a stream, then rainforest, on the other. There’s a metal-roofed shed with open sides, surrounded by dozens of 100-gallon cattle tanks used in experiments. They look like buckets set out to catch an array of extremely large leaks. Vonesh talks about the plumbing system with more enthusiasm than seems possible. “We can fill a cattle tank in three or four minutes!” he exclaims.

All that fast filling means the researchers can do quick experiments other aquatic ecologists can only dream of. Today they’re dismantling an experiment on predation. Four days ago, 47 tadpoles were put in each of 25 tanks along with one Belostomatid, a kind of water bug that eats tadpoles. Today, they’ll count the tadpoles to find out how many the Belostomatids ate.

A giant blue morpho butterfly flits by, its iridescent wings a shocking splash of electric blue against the lush green forest. “They come by, like, the same place at the same time of day,” Warkentin says.

“I swear I see that one every morning,” Vonesh says.

“It’s the 9:15 morpho,” Warkentin says.

Warkentin explains the experiment they’re finishing today. “We know that predators kill prey, obviously, and they also scare prey,” she says. When new-hatched tadpoles fall into a pond, water bugs are one of the threats they face. The tadpoles’ plasticity might help them avoid being eaten—if they can detect the bugs and somehow respond.

Ecologists have developed mathematical equations describing how much prey a predator should be able to eat, and elegant graphs show how populations rise and fall as one eats the other. But what really happens in nature? Does size matter? How many 1-day-old tadpoles does a fully grown water bug eat? How many older, fatter tadpoles? “Obviously, we think small things are easier to catch and eat and stick in your mouth,” Vonesh says. “But we really haven’t incorporated that into even these sort of basic models.”

To figure out how many tadpoles got eaten, the undergraduates, graduate students, professors and a postdoctoral fellow have to get every last tadpole out of each tank to be counted. Vonesh picks up a clear plastic drink cup from the ground by his feet. Inside is a water bug that was feasting on tadpoles. “He’s a big guy,” he says. He reaches into a tank with the net, pulling out tadpoles one or two at a time and putting them in a shallow plastic tub.

“You ready?” asks Randall Jimenez, a graduate student at National University of Costa Rica.


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