Meeting Abstract
Batoids (skates and rays) have specialized jaws that may function independently due to their cartilaginous skeleton, euhyostylic jaw suspension, and the presence of a highly flexible symphysis at the center of the upper and lower jaws. Bilateral implantation of the jaw muscles has lead to a greater understanding of the activity occurring on the left and right sides of the jaw during feeding events. Sharks and skates have demonstrated unilateral activation when feeding on complex prey items. We investigated pairwise activation of the jaw muscles in four species of batoids (Dasyatis sabina, Gymnura micrura, Potamotrygon motoro, Urobatis halleri) from four families in order to examine the evolution of synchronous and asynchronous feeding behaviors. We hypothesized that these rays would use synchronous activation when feeding on small prey and unilateral activation to process larger prey items. Electrodes were implanted bilaterally into four muscles that control the jaws and hyoid. All species were fed squid pieces standardized to one-half mouth width and one mouth width. Two asynchrony indices were used to quantify the duration of muscle activation and the lag, or degree by which muscles are activated out of phase. All rays showed synchronous activation when feeding on both sizes of squid: there was no difference in duration or lag indices (P > 0.05). However, Gymnura were sometimes observed using unilateral activation. Based on the data collected, we hypothesize that asynchronous activation is an ancestral trait of the batoids that has been lost in the derived species. Future studies should incorporate additional derived species to test this hypothesis.
