Biologists turned into puppeteers

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Biologists Wagner Chaves and Emilia Moreno record in silence the aggressive songs of the strawberry poison dart frog Oophaga pumilio

The two researchers choose a spot in a small clearing in the forest. A woman sets up the small stage, positions the puppet and holds its strings. The man accompanying her holds the microphone up, ready to hit the record button. He presses play, and a frog call comes out from a tiny speaker and a male strawberry poison dart frog turns around, puzzled. What will the frog do? Will he call back? Will he fight?

Kermit is not the only frog puppet in the biologist’s world. Herpetologists – biologists who study amphibians and reptiles- are interested in how male frogs defend their territories from other males. Scientists want to understand what it takes to be a winner in these territorial matches. For that, they set up experiments to observe the males’ aggressive behavior. For years, the experiments consisted simply of playing recorded frog calls from a speaker on the forest floor a few feet from a male frog. But a new trend among biologists involves using puppets to study behavior in different species. For frogs, using puppets for behavioral experiments has evolved from Play-Doh figurines to ever-more-complicated models with electronic parts and perfectly matching coloration. However, these dummy frogs have been static, incapable to move back and forth or look “alive.” That is, until now.

Back in the forest, biologists Emilia Moreno and Wagner Chaves sit quietly on the rainforest floor at Costa Rica’s La Selva Biological Station. They are looking for calling males of the strawberry poison dart frog. “We need an enthusiastic male,” says Wagner, “otherwise he will stop calling halfway.” The strawberry poison dart frog is a toxic little fella that lives around fallen leaves, logs and small plants. The frogs choose a spot, and from there they call all day to attract females to their territories. This “love song” for the females also serves as a “Keep Out” sign for other males. However, some feisty males venture to other males’ territories, where the resident male carefully guards a group of females. If the resident male is bigger than the intruder, things can get physical; but if he is small he won’t take risks. At least that’s what Emilia and Wagner expect.

The scientists met about six months ago, while Wagner was doing research on the diet of strawberry poison dart frogs during a tropical biology course at La Selva. Emilia is an entomology research associate at the Pontificia Universidad Catolica de Quito in Ecuador. She studies insects, and when Wagner told her about his project, she recalls, “Since frogs eat bugs, I thought I could help identifying what the ‘pumis’ eat.” She refers affectionately to the frogs with a shorthand for their scientific name, Oophaga pumilio.

Wagner is a seasoned herpetologist who studied amphibians and reptiles throughout his bachelor’s degree in Biology and as a research associate at the Veragua Rainforest Research Center in Costa Rica. Wagner started taking Emilia on walks to show her the frogs around La Selva. “After chasing the frogs around, I couldn’t help but fall in love with those big black eyes,” says Emilia–who also has big black eyes, looking through purple cat-eye glasses. If it wasn’t for the fact Wagner has hazel eyes, one might think she was talking about him and not the frogs.

Together, Wagner and Emilia decided to study whether being a big and well-fed male frog affects the decision to fight back or retreat when an intruder appears.

Oophaga pumilio has been extensively studied, and these tiny frogs’ natural history–their calls, their choices of mates, where they lay their eggs, where they take the tadpoles– is already well known. Emilia and Wagner want to know how males behave when an intruder moves into their territories. Their creative approach to studying the question involves a “dummy pumi,” a puppet frog of sorts with blue legs and red body to resemble the real pumi. Wagner explains that males guard several females in their territory and they don’t want an intruder taking his females away.

Hypothetically, a territorial male is able to determine whether a challenger is bigger than him or not. If the resident male is bigger than the intruder, he will attack the dummy. If he is small, he won’t take risks. Emilia and Wagner’s dummy pumi is a “multimodal signal,” meaning that in addition to the male frog call, they are implementing a visual signal, the intruder. These frogs are active during the day, displaying bright colors due to their poisonous nature. It makes sense to have an intruder that not only sounds like a real frog but it also looks like one.

For the first experimental trial of the day, Emilia sets the dummy on a wooden platform that resembles a fallen log; on the back of the platform sits a small speaker that will broadcast the frog call. Using a pulley system she can move the dummy back and forth and left to right. While she moves the puppet closer to the resident male, she blows air through a tiny hose that connects with the fake frog’s vocal pouch—made of a red-colored condom. Meanwhile, Wagner locates the male and places a long microphone toward the male, so he can record the responses to the intruder. Everything occurs very quietly and they signal to each other when to start and what to do; it’s like Emilia and Wagner have their own secret language now.

During the experimental trial, a peccary, a pig-like tropical creature, comes closer. It seems to look at them and understand they are in the middle of obtaining a data point. It circles around and leaves in silence. The frog comes closer to inspect the puppet; he calls a couple of times but doesn’t seem to care much. “Sometimes they respond very aggressively and sometimes they don’t,” says Wagner. “A few days ago, a very aggressive male jumped on top of the dummy, trying to pin its head down! We were very excited.”

It is the last day of field work and the last chance to get more data. Soon after, Emilia will return to her homeland in South America. Their goodbye will be bittersweet since now they are more than colleagues, more than friends. “The Alliance”–the word they have chosen to define themselves as a team–“separates but it doesn’t end,” she says, smiling at Wagner. Even from a distance, they will analyze the recordings to see the responses of the males. They hope the results support their predictions, but until the analysis is done they cannot know for sure. Emilia says, “Veamos que dicen los sapitos,” which roughly translates as: “Let’s see what the froggies have to say.”

Johana Goyes-Vallejos is a doctoral student in the Ecology and Evolutionary Biology Department at the University of Connecticut. Johana is interested in Evolutionary Behavioral Ecology with a particular interest in amphibians and reptiles. As part of her dissertation she is studying the vocal communication and parental care of the smooth guardian frog of Borneo.
By: Johana Goyes-Vallejos
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