SIUE professor contributes to international research study on toad behavior

During a two-year study, SIUE professor Richard Essner and a team of researchers from Ohio, Missouri and Europe gained insight into the behavior into one of the world’s leading invasive species.

Dr. Richard Essner places a Cane toad into jumping position for filming in Science Building West. By placing digitized landmarks on toad joints, Essner can better understand how knee angles change during hopping motions. (Photo by Joe Lacdan)

Since its introduction to Australia in 1935, the Cane toad has spread from the northeastern coast of Queensland to Western Australia. It has also invaded areas of Florida and the Philippines after it was introduced by humans.

Essner’s study, called “Conquering the world in leaps and bounds: hopping locomotion in toads is actually bounding,” revealed new data on the hopping behavior of the Cane toad, the American toad and the Fowler’s toad. Instead of single, powerful leaps, Essner said the toads go through a series of short hops that not only allowed these species to travel a farther, more efficient distance, but also conserve energy.

The research has drawn international interest and was recently published in the journal Functional Ecology and reported in Science News. The hopping behavior was one of many terrestrial adaptions cane toads used to thrive and spread in new environments.

“It’s given me some insight into why they are so successful as an invasive species,” said Essner, an associate professor.

The research team used data collected by Dr. Lewis Halsey of the University of Roehampton (U.K.). Halsey measured field behaviors ranging from single jumps to multiple jumps with an accelerometer. Meanwhile at SIUE, Essner filmed Cane Toads with a high speed camera in his laboratory in Science Building West and at Ohio University during his sabbatical. After analyzing the film, Essner noticed that during hops the toads did not stop but continued to hop in a continuous motion. These smaller hops essentially are a similar motion to running and are called “bounding gaits.”

“Some of the literature that had been published about toads had indicated when they do these multiple hops, but that they are actually discrete jumps,” Essner said. “So they’ll jump, land, come to a complete stop, really quickly but they would fold up their legs completely and jump again. What we were seeing was more of a continuous gait, where they would extend their legs prior to contact, and use the momentum from their first jump to then drive the second jump.”

This bounding motion allowed Cane toads to travel greater distances and may have helped contribute to their ability spread in a new environment, Essner said. The toads’ locomotion is similar to a mammal but these species of toads have more efficient metabolisms than mammals.

Cane toads, which are native to tropical areas in Central and South America were introduced to Australia and Florida to control insect pests. But their numbers ballooned over the course of several decades.

Essner said the data from the study could help predict the behavior of other species of frogs that may also be considered invasive. Essner said the study led him to research a new aspect area of research–working with Dr. Halsey to study different locomotion types of toads and measure how much energy is used. Essner said he hopes to use accelerometers in the future to study locomotion in a number of different species.

“Hopefully we’ll get some insights into how jumping and landing evolved,” Essner said.

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