Suction Feeding in the Pipid Frog, Hymenochirus boettgeri: Kinematic and Behavioral Considerations
Despite wide variation in form and function of vertebrate feeding strategies, convergent acquisitions of functionally analogous systems are seen across taxa, often driven by the medium (air or water) in which the animal lives. As the majority of fish rely on suction for aquatic prey capture, tetrapods that exhibit this mode prove especially valuable for functional morphological analysis of vertebrate response to medium constraints. The dwarf African clawed frog, Hymenochirus boettgeri, is unique among anurans as an inertial suction feeder. High-speed video recordings indicate that kinematic variables of food capture always proceed in a rostrocaudal sequence, as is conserved among suction-feeding vertebrates. However, maximum hyoid depression differs from most vertebrates studied in that it follows (rather than precedes) mouth closure. Suction events are preceded by a body lunge toward the food item and followed by recoil of the body with lateral spreading of the forelimbs. It is proposed that the abducted forelimbs decelerate the frog's capture lunges and delayed hyoid depression acts to prolong a caudal flow of water to effectively entrain prey.Abstract
Representative capture sequence and mean kinematic profile for seven Hymenochirus boettgeri adults feeding on chironomid larvae (n = 70). (A) The top, middle and bottom rows shows representative, non-sequential high-speed video frames of anterior, lateral and ventral views, respectively. Each vertical column of three images depicts a specific moment in the feeding sequence (illustrated by the black millisecond bars in the top row). Gray, tapered triangles indicate the location of that event on the kinematic profile, Figure 1B. In A., note the maximum hyoid protraction (white arrow) as well as the prey item (black arrow) as it moves into the buccal cavity. (B) Durations of variables are plotted as a function of time in milliseconds with standard error bars. To clarify the “gape cycle,” the recoil event (which begins at approximately 72 msec and is much larger than the gape cycle) is removed
Distances covered between high-speed video frames (250 fps) for predator and food from one representative feeding sequence of adult Hymenochirus boettgeri feeding on non-living chironomid larvae. Dpred and Dfood are the net distance moved by the predator and prey respectively with 8.0 msec between each data point. Onset of mandibular depression is time zero
Contributor Notes
Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, California 92697-2525. mdean@uci.edu.