24 May 2019
Urban male frogs flirt better than rural peers
Published online 12 December 2018
Male túngara frogs are free to sing their hearts out in the cities, and the females love it.
Male túngara frogs (Physalaemus pustulosus) — amphibians native to Central America — adjust their mating calls to urban environments to become more attractive, reports a new study.
During the rainy season, male frogs gather in puddles after sunset to call and attract potential partners. Unlike most other frog species, túngara frogs are able to vary their mating calls. Besides their basic love song tune, they can add extra vocal elements, called chucks, which sound like video game beeps from the 1990s to us, that lure in female frogs. These more elaborate calls, however, also catch the attention of unwanted eavesdroppers, such as frog-eating bats and parasitic midges.
A research team, including a scientist affiliated to the University of New York at Abu Dhabi, recorded 98 male frogs in 11 urban and 11 forest sites around the Panama Canal, and observed that city frogs call more often and introduce more chucks. This could be explained by different selection pressures inside cities, such as higher competition over females, but lower risks of predation and parasitism.
The researchers also found that three quarters of the female frogs studied, regardless of their origin, preferred the complex urban calls over the simpler rural ones, and that urban males are very flexible in adjusting their call complexity. They transferred some of these amphibians from cities to forests, and vice versa, under controlled conditions. In both cases, the frogs tended to change their call frequency, likely as a response to the difference in noise and light levels. However, while urban males reduced the number of chucks per call in the forest environment, forest dwellers did not adjust their love songs to the new conditions.
“Urban males can match the performance of forest frogs in the forest, and outcompete them in the city,” says the study’s lead author Wouter Halfwerk of Vrije Universiteit in The Netherlands. “Over long periods of time, if urban areas are replacing more and more natural areas, at some point you would expect forest males to disappear altogether.”
In the future, Halfwerk is planning to conduct molecular analyses and breeding experiments to understand whether the observed differences are genetic and heritable.
Cities are becoming a hotbed for studying how wildlife is adapting to life alongside humans, and how they use cities to their advantage. This study’s results indicate that frogs that are more flexible and less risk averse prosper well in cities, but are other species of frogs easily adaptable to the urban environment? Or are these urban túngara frogs somehow lucky? “Only comparable studies of other species can begin to answer these questions,” says herpetologist Carl Gerhardt of the University of Missouri in the U.S., who was not involved in the study.
Halfwerk W. et al. Adaptive changes in sexual signalling in response to urbanization. Nat. Ecol. Evol. https://doi.org/10.1038/s41559-018-0751-8 (2018).