Sexier frogs in the city

Male tungara frogs living in urban environments are more attractive to females than those living in forests because they have more complex vocal calls, suggests a study published online this week in Nature Ecology & Evolution. The findings also suggest that frogs in urban areas favour more conspicuous calls because they have fewer predators in than those in natural habitats.

The expansion of manmade environments in the natural world can cause problems for animal communication, with noise and light pollution interfering with visual and auditory signals.

Wouter Halfwerk and colleagues investigate how city life has altered the signalling behaviour of male tungara frogs. The authors recorded the characteristic ‘chuck’ calls of frogs living in both urban areas and forests near the Panama Canal. They found that urban males call more often and with greater call complexity than their forest counterparts. The authors played back the urban and forest calls to female tungara frogs in the lab, finding that three-quarters of the females were more attracted to the more complex urban calls.

Moving both tungara urban frogs into forest habitats and forest tungara frogs into urban habitats, the authors found that urban frogs could actively reduce the complexity of their calls in the new environment. However, forest frogs did not increase their call complexity in urban habitats. The authors suggest that evolution has selected for greater call flexibility in the urban world, where fewer eavesdropping predators were found compared to the forest, and so the risks of being overheard are lower.