Sticky and Fast: Jumping and Landing of the Cuban Tree Frog (Osteopilus septentrionalis)
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When landing from a jump or fall, humans and other mammals, such as cats and monkeys, modulate the timing and degree of activation of limb muscles in mid-air in response to fall height. Recent work revealed the presence of this behavior in Cane toads (Bufo marinus), the first non-mammalian animal in which it has been identified. These toads exhibited tuning of the timing and intensity of pre-landing recruitment in elbow antagonists in accordance with hop distance. Specifically, longer hops led to more intense and later activation of pre-landing muscle activity. To investigate the conservation of this behavior among other anurans, I studied landing in Osteopilus septentrionalis, commonly known as the Cuban tree frog. In particular, I addressed if these animals were capable of altering forelimb muscle activation patterns in preparation for landing in response to hop distance. I also examined if any differences exist between preparations for landing on horizontal versus vertical surfaces. Using high-speed video, I tracked the limb positions during jumps onto surfaces of different orientation. I also implanted fine-wire electrodes into two forelimb muscles, the deltoideus scapularis, which acts at the shoulder, and the coracoradialis, which acts at the elbow, in four jumping tree frogs. Electromyographical recordings measuring the timing and intensity of the muscle activation were characterized from the onset of movement through landing. These tree frogs demonstrated different forelimb kinematics and muscle activation patterns between jumps to vertical versus horizontal surfaces. Furthermore, when hopping onto a horizontal surface, these animals exhibited tuning in the intensity and timing of their pre-landing muscle recruitment in these two muscles. However, when jumping to a vertical surface tuning was not present.
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