MONROY, Jenna/A; Northern Arizona University: Hypoglossal feedback as a function of prey location in Dyscophus guineti
Like other microhylid frogs, Dyscophus guineti uses a muscular hydrostatic mechanism to elongate and aim its tongue independently of its head during prey capture. However, tongue projection velocities can be more than 10x higher than in other microhylids. Dyscophus tongues reach velocities of 3 m/s with accelerations more than 50x gravity. In contrast, the tongues of most microhylids reach maximum velocities of 0.4 m/s and accelerations of about 3.5 m/s 2. Other frogs that achieve as high velocities as Dyscophus use transfer of momentum from the lower jaw to the tongue to throw the tongue from the mouth. This mechanism of protraction requires sensory feedback from the tongue to precisely coordinate movements. It was hypothesized that Dyscophus evolved tongue afferents independently to coordinate jaw and tongue movements. Nerve transection experiments combined with high-speed imaging and electromyography were used to characterize a prey location-dependent hypoglossal feedback system that coordinates mouth opening and tongue protraction. When feeding on prey directly in front of the frog, sensory feedback from the tongue traveling through the hypoglosssal nerve is necessary to trigger mouth opening. Transection of the hypoglossal nerve prevents the mouth from opening. However, when feeding on prey to the side, the mouth opens normally even after the hypoglossal nerve has been transected. Thus, peripheral feedback is not necessary to trigger mouth opening when the tongue is aimed to the side. Dyscophus uses a muscular hydrostatic mechanism to elongate and aim the tongue to the side and an inertial elongation mechanism to amplify protraction speed when feeding on prey straight ahead. These data suggest a neuronal mechanism for modulating feeding motor output in response to prey location.
