The role of visual perception in the hopping locomotion of rhinella marina.
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Hopping is a saltatory form of locomotion utilized by a diverse range of species across the animal kingdom. The Cane Toad, Rhinella marina, is a common model used to examine this movement, due to its ability to sustain continuous hopping over significant durations of distance and time. This locomotion requires immense muscular coordination, and is mainly achieved through anticipatory forelimb contractions prior to a landing, known as muscle tuning. Tuned reactions enable the toad to both dissipate landing forces through eccentric muscle contractions, as well as reduce the time necessary to prepare for its next hop. Forelimb tuning is a complex process with multiple mechanisms at play, including both visual and non-visual perceptive components. This research aims to understand what role visual perception plays in hopping. This was accomplished by observing hopping mechanics in Cane Toads with vision, and then with it eliminated. Five Cane Toads were marked at the elbow, wrist, midway on the humerus, and along the longitudinal axis of the back. Each toad was recorded performing 15 hops on two HiSpec Lite cameras (500fps). They were then anesthetized, and their optic nerves severed. Upon recovery, the Cane Toads performed another 15 hops. The three-dimensional position of each marker was digitized using DLTdataviewer2, a point-tracking MatLab script. Using custom MatLab scripting, elbow extension/flexion angle, humeral protraction/retraction angle, and humeral elevation/depression angle were calculated for each frame of each hop video. These angles were analyzed via mixed generalized linear models. General trends included that blind toads seemed to typically be more flexed, retracted, and depressed than sighted toads, who were consequently more extended, protracted and depressed. These results indicate that vision plays a role as more of a “fine tuning” mechanism.
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