Athletic frogs: Go bold or go home

U. TEXAS-AUSTIN (US) — The most toxic, brightly colored members of the poison frog family also may be the best athletes.

The poison dart frogs of the Amazon jungle, so-named because some tribes use their skin secretions to poison their darts, are well known for their bitter taste and beautiful colors. The spectacular hues of these forest frogs serve to broadcast their built-in chemical weapons: skin secretions containing nasty toxins called alkaloids.

Like the red, yellow, and black bands on a coral snake or the yellow stripes on a wasp, their contrasting color patterns warn would-be predators to stay away, says Juan Santos of the National Evolutionary Synthesis Center in Durham, North Carolina, who is lead author of a new study in the journal Proceedings of the National Academy of Sciences.

As it turns out, the most boldly colored and bad-tasting species are also the most physically fit.

In forests in Colombia, Ecuador, Venezuela, and Panamá, Santos subjected nearly 500 poison frogs—representing more than 50 species—to a frog fitness test. He measured their oxygen uptake during exercise using a rotating plastic tube, turning the tube like a hamster wheel to make the frogs walk.

Santos estimated the frogs’ metabolic rates while at rest, and again after four minutes of exercise. The result? The most dazzling and deadly species had higher aerobic capacity than their drab, nontoxic cousins.

“They’re better able to extract oxygen from each breath and transport it to their muscles, just like well-trained athletes,” says Santos, a former graduate student at the University of Texas at Austin.

Poisonous species owe their athletic prowess to their unusual foraging habits, explains co-author David Cannatella of the University of Texas at Austin. Unlike snakes and other poisonous animals that make their own venom, poison frogs get their toxins from their food.

“They acquire their alkaloid chemicals by eating ants and mites,” Cannatella says.

Because of their picky diet, poisonous frogs have to forage far and wide for food.

“Nontoxic species basically stay in one place and don’t move very much and eat any insect that comes close to them,” Santos says. “But the bright, poisonous frogs are very picky about what they eat.”

“It’s not like a buffet where they can get everything they need to eat in one place,” Cannatella adds. “Ants and mites are patchy, so the frogs have to move around more to find enough to eat.”

This combination of toxic skin and bold colors—a syndrome known as aposematism—evolved in tandem with specialized diet and physical fitness multiple times across the poison frog family tree, the authors explain.

In some cases the frogs’ physical fitness may have evolved before their unusual diet, making it possible to forage for harder-to-find food. But Santos says the specific sequence of events was likely different for different branches of the tree.

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