Some frogs contain enough poison to kill 10 grown men. You might think that would make them able to withstand whatever Mother Nature decides to throw at them, but you’d be wrong. It turns out that those amphibian species that use chemicals as their main defensive trait are actually the most vulnerable to extinction.
Animals use all sorts of different tactics to avoid being eaten, such as subtle camouflage or fearsome spines. But some groups of amphibians have taken the method of producing deadly poisons under their skin and run with it. It’s been suggested that the ability to produce such poisons has helped these amphibians to split into more and more species, as they’re able to move into environments that their less deadly cousins can’t survive in. But it seems, paradoxically, that it also makes the species more at risk of dying out completely.
In the study, researchers looked at how the rates of speciation – that is how quickly one species will evolve into other species – and extinction varied across amphibians with different defensive tactics. They found that while the development of bright, conspicuous coloration was associated with an increase in speciation, if those amphibians in question also produced the corresponding poisons, their extinction rate also went up. If the frogs were simply mimicking the more deadly varieties by copying their coloration but without producing the associated deadly chemicals, then their extinction rate remained unchanged.
The researchers, from the University of Liverpool, don’t yet have the data to determine why this quirk might be, though they do have a number of possibilities. It could be that while the frogs are capable of rapid speciation, the environments the animals have become adapted to are so niche and resource-poor, they can’t support large numbers of each individual type, thus increasing susceptibility to extinction. Or perhaps the development of chemicals causes a shift towards those species having slower life histories, which again would make them more sensitive to extinction.
“There are a number of plausible reasons why the use of chemical defence might lead to higher extinction rates,” explains Dr. Kevin Arbuckle, who co-authored the study published in the Proceedings of the National Academy of Science. “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.”
This finding, while confirming the previous suggestions that evolving conspicuous coloration increases speciation, shows that, as always, things are never that simple. The researchers hope that this information could help the conservation of endangered species by allowing a degree of predictability of which animals are most at risk.
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