The little devil frog’s fearlessness in the face of hungry predators could be down to his toxicity. The little devil, Oophaga sylvatica, is a member of the dendrobatid group of poisonous frogs. His bright colours warn predators that he is unsafe to eat, which Juan Santos of the University of British Columbia in Vancouver, Canada, believes has allowed the evolution of more flamboyant mating calls.
Santos and his colleagues examined the calls, colourings and toxicity of 170 species of frog, including the little devil. They found a strong relationship between the volume of a frog’s call and its aposematism – markings that warn of its toxicity. In general, the more toxic a frog, the brighter and more noticeable it is – and the louder and more rapidly it sings (Proceedings of the Royal Society B ). Non-toxic frogs are camouflaged and call from less exposed perches, says Santos.
“Females can have a significant effect on the selection of the most noisy males, given that predators will avoid these aposematic individuals,” says Santos.
The male’s calls can travel over long distances, in an attempt to attract a mate. But it’s not just about attracting a female frog’s attention – it’s about letting her know how desirable he is.
“Calling is a very demanding activity and only healthy individuals have the capacity to produce continuous bouts of acoustic signals,” says Santos. The larger the animal, the lower the tone of the call, meaning that they also provide information about the size of the singer. And they also help the female to locate the male – crucial when travelling through the jungle in search of a frog only around 3 centimetres in size.