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Predator Defenses Backfired: Poisonous Frogs Face Higher Risk Of Extinction, Researchers Say

Oct 20, 2015 05:57 PM EDT
Blue Poison-Dart Frog
Some amphibians, such as the blue poison-dart frog (pictured here), that use chemical defenses against predation are actually at a higher risk of extinction.
(Photo : Wikimedia Commons )

Sometimes, being the most poisonous in the bunch isn't the best defense, it seems. In order to escape predation, many species have evolved to use special defenses that include camouflaging themselves, mimicking other species or using chemicals. For some amphibians that use toxins to protect themselves, the self-defense plan has backfired. Researchers from the University of Liverpool recently discovered that this predatory defense puts animals such as the iconic poison-dart frogs at a higher risk of extinction.

For their study, a team of researchers examined how the rate of amphibian extinction and speciation (the formation of new species) varied based on the use of different defensive measures. While those animals that produced poisonous chemicals as a predatory defense had a high rate of speciation, populations also exhibited a greater rate of extinction, researchers concluded. Ultimately, this leads to a net reduction in species diversification -- a combination of both speciation and extinction rates -- which the species was trying to avoid by using predatory defenses in the first place, according to a news release.

On the other hand, researchers found that amphibians that changed the color of their skin to hide or those that mimicked their predators to confuse them were using much safer methods of self-defense. The animals that used these techniques were able to both increase and expand (sometimes called "radiating") their range, and increase the number of species to avoid an increasing rate of extinction, the release noted.

"There are a number of plausible reasons why the use of chemical defense might lead to higher extinction rates," Dr. Kevin Arbuckle, lead author of the study from the University of Liverpool's Institute of Integrative Biology study, explained in a statement. "For example, it could be that there is trade off which leaves prey vulnerable to other kinds of enemies, such as infectious diseases, but we don't yet understand what drives the relationship."

The long-held evolutionary hypothesis, "escape-and-radiate," predicts that animals will develop defenses that allow them to escape the threats of predation. The idea is that this diversification leads to speciation. However, researchers noted that this theory does not factor in extinction rates. Further research is also needed to explain how and why chemical defenses, such potentially lethal toxins released from the skin of poison-dart frogs, are related to increased extinction rates. 

"We've shown that this hypothesis, which is widely cited and used, requires some revision because of its failure to account for the effects of extinction rates. We propose that 'escape-and-radiate' should be seen as just one part of a more general hypothesis for the macroevolutionary effects of antipredator defense that includes both speciation and extinction," Arbuckle added. 

Their study, recently published in the journal Proceedings of the National Academy of Sciences, sheds light on how developing such predatory defenses can ultimately affect a species' survival. This could help conservationists better protect endangered species in the future.  

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