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Female frogs prefer city slickers

Anyone who has tried to whisper sweet nothings into their lover’s ear while standing on a noisy street corner can understand the plight of the túngara frog. A tiny amphibian about the size of a U.S. quarter, the male Physalaemus pustulosus has had to make its call more complex to woo mates when they move from the forest to the city. Now, researchers have found that female túngara frogs from both the country and the city prefer these mouthy city slickers.

Biologists have long studied túngara frog courtship, demonstrating that visual signals and calls by themselves are unattractive to females but together are a winning combination, and that a female’s decision to mate depends on the context. Now, researchers have recorded the calls of male frogs living in cities, small towns, and forests across Panama. As they played the calls back, they counted the females, frog-eating bats, and frog-biting insects lured in by each call. Then they transplanted forest-dwelling frogs to the city and city dwellers to the forest to see how females there reacted to their calls. Finally, in the lab, they tested female preference for each call.

Males living in cities and towns called more frequently and had more complex calls—with louder “chucks” interspersed in the whine—than forest frogs, the team reports today in Nature Ecology & Evolution. When they were moved into the country, they simplified their calls; but when their country cousins were brought to the big city, they couldn’t make the switch, and kept singing simply. When the researchers played back the calls to females, the females preferred more complex calls, even if the female herself was from the country, they reported.

Thus, the city frogs not only upped their game, but they were also able to adjust to being in the country again. Because the more complex calls attract more predators and pests, it’s likely that country frogs never added the loud “chucks” to their repertoire, the researchers note. But given that urban areas have fewer bats and insects, the city frogs suffer no penalty for jazzing up their love songs.