Wilga, Cheryl [faculty advisor, Department of Biological Sciences]
functional morphology; elasmobranchs; feeding
Feeding mechanisms of aquatic vertebrates has been extensively studied in the past, while that of elasmobranchs remains limited. Skates and rays are believed to have evolved from a shark ancestor, thus they represent the most derived group. All skates are dorsoventrally compressed, have a unique jaw suspension type and head skeleton and live in benthic environments. It is unknown whether these derived features of skates have altered the ancestral shark feeding mechanism. Comparing feeding mechanisms in skates and sharks may shed light on morphological transformations that have arisen after the evolutionary split of these two groups. In this study prey capture and manipulation behaviors are compared and contrasted with the white-spotted bamboo shark. Jaw kinematics and buccal pressure during feeding events are investigated using sonomicrometry simultaneously with pressure transducers. Little skates capture prey primarily using biting but sometimes utilize weak suction as well. Pressure in the buccal cavity during prey capture varies around ambient ranging from slightly positive to slightly negative. In contrast bamboo sharks always use strong suction to capture prey with greater subambient buccal pressures. However, both species extensively process prey using strong suction alternately with compression. Such cycles can last several seconds, eventually ending in transport of the prey item. Greater subambient pressure develops in the buccal cavity during manipulation, indicating that skates are capable of generating stronger suction than that used to capture prey. Gape area during capture events is greater than during manipulation. Hyoid area attains similar magnitudes in both capture and manipulation events. Time of mean onset and peak gape and hyoid expansion occurs prior to peak buccal pressure in captures and manipulations. Although both occupy benthic regions of the ocean, prey capture in the two species appears to be quite different while manipulations are similar. Morphological differences in the jaw and hyoid apparatus of sharks and skates may be partly responsible for the functional differences in the generation of suction.