Poisonous Problems: Chemical Defenses Come With Evolutionary Cost

The chemical weaponry of this beautiful little dart frog come at a high evolutionary cost. Photo by Dirk Ercken Poison dart frogs are some of the most stunning species on Earth. But their vivid colors aren't for aesthetics: they're meant as a warning to potential predators. For while these frogs are visually stimulating, they are also armed with potent toxins. The poisons in their skin are so powerful that local tribes have been known to create deadly darts simply by rubbing them on the frogs' backs — hence the name. One might expect that the evolution of such a successful defense would allow these frogs to diversify faster than their relatives and outcompete their kin for resources and habitats — and, according to a study published in the early edition of Proceedings of the National Academy of Sciences this week, their toxins do give them a speciation advantage. But, their defenses don't come cheap: poisonous frog species also go extinct at a faster rate. "Amphibians are facing global population declines and extinctions," explained Kevin Arbuckle, a herpetologist and evolutionary biologist at the University of Liverpool. "I thought it might be useful to figure out whether defense can influence their chances of diversifying or going extinct." Arbuckle was interested in testing a hypothesis proposed fifty years ago, known as "escape and radiate". The hypothesis predicts that the development of a new way of avoiding being eaten — such as a defensive toxin or camouflage — should allow an animal lineage to diversify faster than others. Thus, one would predict that lineages with such antipredator adaptations would have more species than those without.