Study in Schönbrunn

Why the Titicaca giant frog does push-ups

(Bild: APA/Tiergarten Schönbrunn/Rupert Kainradl)

The appearance of the highly endangered Titicaca giant frogs is rather bizarre with their particularly wrinkled skin. The animals' behavior also seems strange, as they sometimes appear to do "push-ups" under water. A study has now revealed why they do this.

The Titicaca giant frog (also known as the Titicaca frog or Titicaca lake frog) is the largest frog in the world that lives exclusively in water and breathes almost exclusively through its oversized skin. In collaboration with Brown University, Schönbrunn Zoo has now been able to show in a study that the amphibians frequently perform "underwater push-ups" under particularly low-oxygen conditions.

Movement probably supports skin respiration
The animals probably adopted this method to support skin respiration. "The folds in the frog's skin increase its surface area. The 'push-ups' move the folds, allowing oxygen to be absorbed from the surrounding water," the researchers report in the journal "Behavioral Processes".

(Bild: APA/AFP/Aizar Raldes)

The Titicaca giant frog lives in water depths of up to one hundred meters and is threatened with extinction.

(Bild: Wikipedia/Zoo Praha/Petr Hamernik (CC BY-SA 4.0))

This is particularly advantageous in the frogs' natural habitat, Lake Titicaca in the west of South America. "Due to the altitude and the resulting low air pressure, conditions there are often low in oxygen," says zoo director Stephan Hering-Hagenbeck.

The researchers used nitrogen gas to simulate the low-oxygen environment of frogs in the wild in experimental tanks at Vienna Zoo. According to the press release, the gas partially displaces the oxygen dissolved in the water. They initially observed that the frogs reduced their activity. As soon as the oxygen content of the cool water dropped even further, the animals began to do their "push-ups".

Behavior improves gas exchange in the water
"The 'push-up behavior' possibly improves the gas exchange between the frog's skin and the water, as the oxygen-poor boundary layer around the skin folds is interrupted. This behavior thus represents an exciting adaptation of the animals to quickly cover their oxygen requirements," says Doris Preininger, a research associate at Schönbrunn Zoo who was involved in the study.

Animal is threatened with extinction
The Titicaca giant frog is only found in Lake Titicaca - the largest lake in South America, which belongs to Bolivia and Peru. It can reach a head-to-torso length of up to 20 centimetres, lives in water depths of up to one hundred meters and is threatened with extinction. At Schönbrunn Zoo, the Titicaca frog is bred quite successfully - also for research purposes.