The love pad: UWM lab tests fr When it’s time to mate, female eastern gray tree frogs venture at night toward the pond, where they are bombarded by a chorus of hundreds of male frogs singing with pulsed “chirps” that differ in pitch, duration, volume and repetition. The collective serenade goes on for hours, though individual males take breaks. “Male calling has been described as the most energetically challenging behavior of any vertebrate,” said Gerlinde Höbel, “and the competition is stiff. Males pay attention to what other males are doing, and they push themselves as far as they can.” With so much variation to choose from, how does a female decide which she’ll respond to? The question would be impossible to study in a natural setting because of the sheer volume calls and their traits, said Höbel, an associate professor of biological sciences at UWM. Instead, Höbel and her students bring frogs they’ve caught to an environment specifically designed for tree frog romance in the lab. Inside what looks like a large walk-in freezer in Lapham Hall is a simulated setting, dubbed the “frog arena.” Here, Höbel and her lab members are teasing apart what the different types of vocalizations might mean and using the arena to investigate an assortment of questions about frog communication, including female preferences to calls.
Researchers, including doctoral students Olivia Feagles (from left, holding an amphibian friend) and Kane S inside their “frog arena.” (UWM Photo/Troye Fox)
The stakes couldn’t be higher: Most females will mate only once in their lives, while many males will not find a mate at all. So answers to mating behavior questions have evolutionary implications, Höbel said. It’s the females who often drive sexual selection, a preference by one sex for certain characteristics in those of the other sex, she said. “Much of the amazing mating diversity we see in nature – like songs, plumage color and dances – are the outcome of sexual selection by female choice. Sexual selection is one of the main drivers of biological diversity.” Traits and tribulations
Artificial ‘frog arena’ tests how females choose a mate
10 • IN FOCUS • October, 2021
Conditions inside the frog arena can be controlled to mimic the pond. The temperature is kept at 68 degrees, and a nightlight provides just enough light. The walls are covered in acoustic foam, which prevents the sound distortions that occur indoors. In a circular clearing on the floor, the researchers have placed small speakers around the circumference. In the
