Scientists visualize high-speed swallow response in toads

Wednesday, November 16, 2022

In findings published in Integrative Organismal Biology, scientists from the Florida Museum of Natural History have described the mechanism by which the cane toad (Rhinella marina) swallows its food, a feat that has long eluded scientists for all anuran (frog and toad) species.

Because of the rapidity with which frogs and toads capture and engulf their prey, the physical process by which they bring the food from their environment to their stomachs was almost impossible to study until the invention of high-speed cameras in the 20th century. Even then, scientists could only study events that took place outside the animals’ bodies, such as the way the tongue unrolls to grab an insect.

The researchers solved this problem by surgically attaching tiny metal beads to various structures inside the bodies of live toads: the pectoral girdle, tongue, and hyoid apparatus. They then placed three test animals in clear boxes and recorded themusing a high-speed X-ray technique called X-ray Reconstruction of Moving Morphology as they ate a series of crickets. This allowed them to visualize the process in three dimensions.

Findings showed that the entire bottom surface of the toads’ mouths moved backwards down the throat, tongue and all. The tongue is attached to a complex cartilaginous structure called the hyoid, which seems to help the frog remove the insect from its tongue by pressing the tongue against the roof of the mouth. The toad’s tongue is quite sticky. The physical infrastructure needed to do this is so extensive that it bumps against the frog’s heart.

“We know a lot about how frogs extend their tongues and how it sticks to their prey, but prior to this study, essentially everything that happens after they close their mouths was a mystery,” said lead author Rachel Keeffe, who had been working toward her doctorate at the University of Florida at the time of the study.

The scientists chose the cane toad because of its large size, which made the study easier to perform. They believe these results can be extrapolated to other toads and frogs, but further studies must be performed to be certain.

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