Meeting Abstract

70.5  Jan. 7  Asynchronous bilateral jaw muscle activity in two species of elasmobranchs GERRY, S.P.*; DEAN, M.N.; SUMMERS, C.D.; WILGA, ; Univ. of Rhode Island; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of Rhode Island sgerry@mail.uri.edu

Complex prey processing in higher vertebrates is characterized by unilateral activation of the jaw musculature, permitting freedom of movement through partial decoupling of the sides of the head. This has had limited demonstration in lower vertebrates where the symphyses between the halves of the jaw tend to be more flexible than those of mammals, suggesting that the flexibility in the lower vertebrate feeding mechanism lies within the morphology of the jaws and not their muscular control. Using electromyography, we demonstrate asynchronous bilateral jaw muscle activity in members of two major groups of elasmobranchs, spiny dogfish, Squalus acanthias, and little skates, Leucoraja erinacea. Both species possess flexible symphyses and are known to modulate their feeding behaviors in response to multiple prey types. Electrodes were implanted in an unpaired jaw opener (coracomandibularis) for reference and bilaterally in three of the jaw adductors: two divisions of the quadratomandibularis and the preorbitalis. In dogfish, electrodes were also implanted in a cranial elevator (epaxialis). During prey capture bilateral jaw muscle pairs were activated synchronously in both species, but asynchronously during prey processing. This illustrates a previously unappreciated flexibility of the elasmobranch feeding mechanism in that jaw muscle activity can be modulated both unilaterally and bilaterally in response to prey type. These findings imply that asynchronous activation of the jaw muscles is an ancestral characteristic of vertebrates and perhaps arose with the derivation of jaws.