City frogs have sexier calls than country frogs, study finds
Living in a forest might sound romantic, but city life makes males more attractive to the opposite sex – at least if you are a túngara frog.
Researchers have discovered that urban males of the species have more attractive calls than their rural peers.
The scientists say this is down to greater competition for mates, meaning the frogs need to unleash their sexiest sounds to win over a female. P| redators and parasites are also rarer in urban areas, so the frogs do not have to fret about attracting the wrong sort of attention.
“There is no constraint, they can go wild,” said Prof Wouter Halfwerk, coauthor of the study from Vrije University in Amsterdam.
Writing in the journal Nature Ecology and Evolution, Halfwerk and colleagues report on their findings from studying 11 rural and 11 urban areas along the Panama canal during the rainy season.
They recorded the calls of male túngara frogs, which begin as a sort of a whine before vibrations called chucks are added, producing a noise that would not be out of place in a game of Space Invaders. “The larynx is bigger than their brain,” said Halfwerk.
The team found that urban frogs call more, and with more complex vocalisations, than those in forest locations.
When they broadcast a generic computer-generated frog call in both environments, they found fewer female frogs were attracted to it in the city. The researchers believe there are simply fewer females living in the urban areas, although they said it was not clear why. Male frogs were found to have similar numbers of rivals regardless of location, meaning there was more competition for females.
“It is harder for males to get mates in the city and so that is why they even have to work harder than their forest counterparts to get the females,” said Halfwerk.
Further work with 20 forest and 20 urban females revealed both preferred to hop toward a speaker playing the elaborate call of an urban male than a forest frog’s simpler effort, even if both were recorded with the same background noise. In other words, the urban call was sexier. .
Halfwerk said the divergence suggests frogs that have wound up in the city might have a different larynx, hormone levels or even a neural difference that allows them to make more complex calls.
The team now plan to do genetic studies and a large-scale breeding project to see whether the differences are passed on down through generations.
Stuart West, a professor of evolutionary biology at the University of Oxford who was not involved in the study, called the research elegant. “Human activity is having a huge impact on the environments that animals live in,” he said. “This study shows that it can even influence what males have to do to attract mates.”