By 2050, nearly 70 percent of the world's population will live in urban environments, according to the United Nations. But as cities spread, wild animals will also have to adapt. In Nature Ecology and Evolution, researchers working at the Smithsonian Tropical Research Institute (STRI) report that male tuna frogs in Panama City make mating exhibitions more attractive than frogs living in nearby tropical forests.
"The tuna frogs sounds a bit like pinball machines", commented Wouter Halfwerk, associate professor at the Vrije Amsterdam University, and visited a researcher at STRI. "For their simple tuning sound, they can add additional elements like audio, gara, to make complex calls: tun gara gara, hence its name.
Some call the tuna tuna the acoustic equivalents of peacocks. They are not colorful at all, but like the male peacocks that have elegant tails to attract females, tuna frogs add extra sounds to their call to find a friend. "
But female frogs are not the only ones watching men's love songs. Predatory bats and parasitic flies use the same calls to find their dinner. So frogs do not add extra garas when they know that carnivores are present.
In Panama City, Tuna's frogs live in various urban environments: from ditches and puddles in neighborhoods near tropical forests to drainage between downtown skyscrapers. How does the frogs compare with the forest groves when they call to attract the females?
In their first attempt, the Halfwerk team recorded footage of male tungaras in 22 towns and villages and recorded the number of women, predators and parasites that approached infrared infrared cameras.
In the city, fewer women answered the calls. Perhaps fewer women were available or the men had to work harder to get their attention. In addition, the so-called prints do not attract bats and only a few flies, suggesting that carnivores are a minor threat to the city.
To find out if towners customize their calls, they recorded up to one hundred calls in the same places and found out that urban men call higher rates using more complex and eye-catching calls than frogs in the forest. Forty women chose between horns who played the call of an urban man or one of the forests. Three out of four women preferred calls to townspeople.
Finally, they wondered how quickly the frogs adapted their calls. When they took the forest frogs to the city and the frogs from the city to the forest, they discovered that the urban men in the forest immediately switched to easier calls, corresponding to the men of the forest while the forest is men in the city. They do not make more complex calls immediately.
The deciding factor for these changes in men's call seems to be a greater competition for women and fewer predators and parasites in the city.
"Just as we change our social relationships in cities, animals change their relationships and behaviors in the radically changing biological communities that we create around the world" commented Rachel Page, STRI's staff researcher and kautor.
The co-authors include Gettysburg College, Purdue University, University of New York, Abu Dhabi and University of Texas. The funds for this study were provided by a Marie Curie Fellowship, a Veni Fellowship, the Ecology Foundation for the Royal Danish Academy of Fine Arts and Dutch Science and the National Science Foundation in the United States.
Reference: Halfwerk W, Blaas M, Kramer L., Hijner N, Trillo PA, Bernal XE, Page RA, Goutte S, Ryan MJ, Ellers J. 2018. Adaptive changes in sexual signaling in response to urbanization. Nature Ecology & Evolution. Doi: 10,1038 / s41559-018-0751-8