After testing hundreds of frogs representing dozens of species on an amphibian version of a treadmill, researchers have determined that colorful, highly poisonous frogs have the greatest aerobic capacities.

Earlier studies had suggested a link between poison and metabolism in frogs, but involved just a handful species.

Of course, unless you’ve always dreamed of putting frogs on treadmills, or plan to bet on frog races, the results might seem a bit academic. But they raise a fascinating natural history question: Why are colorful, poisonous frogs the fittest?

University of Texas, Austin, biologists Juan Santos and David Cannatella, who described their frog experiments March 28 in the Proceedings of the National Academy of Sciences, have a few ideas.

In frogs, especially bright colors generally signify toxicity, informing predators of their prospective meal’s unpalatability. But whereas most poisonous animals produce venom naturally, the frogs distill it from their food.

To find the right insects, they forage far and wide, rather than waiting for whatever fare passes by. Evolution would seem to have produced aerobic adaptations that help poisonous frogs roam, then amplified coloration as a defensive signal.

It’s also possible that bright coloration evolved first, providing some sort of advantage — predator defense, perhaps, or help finding mates — that allowed those frogs to range farther than their drab brethren. That in turn could have allowed them to specialize in eating uncommon, toxin-enabling insects.

Both evolutionary paths are likely represented among poisonous frogs, wrote Santos and Cannatella. To study these questions in further detail, new methodologies would help — including, perhaps, analyses on frog coloration as seen through their predators’ eyes, rather than our own.

Image: Poison dart frog (Tambako the Jaguar/Flickr)

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Citation: “Phenotypic integration emerges from aposematism and scale in poison frogs.” By Juan C. Santos and David C. Cannatella. Proceedings of the National Academy of Sciences, published online before print, March 28, 2011.