Meeting Abstract
79.4 Sunday, Jan. 6 Strain in the Hyomandibular Cartilage of Elasmobranchs WILGA, C*; SAKAI, S; Univ Rhode Island cwilga@uri.edu
The main jaw suspensory element, the hyomandibula, determines jaw mobility in elasmobranchs and ranges from slender and posteriorly directed in wide gaped bite feeders, to block-like and laterally directed in smaller mouthed suction feeders, to slender and anteriorly directed in skates and rays, which have ventrally oriented mouths. This diversity in jaw suspension morphology and feeding style will impose different levels and type of mechanical strain in the hyomandibula when feeding. Here we measure biological load in vivo with the goal of understanding the performance of cartilaginous elements with clear morphological and kinematic differences. Sonomicrometry uses ultrasound to measure distance and is used to quantify applied biological load and function. Strain in spiny dogfish and little skates was quantified using sonometric transducers firmly glued to the ventral surface of the hyomandibular cartilage. Another transducer was sutured to cranium adjacent to the hyomandibula to record hyoid movements. Results show that strain is tensile in the hyomandibula of dogfish and increases with mouth opening during suction feeding and ventilation. Strain is lowest in normal ventilation, intermediate in heavy ventilation, and highest in suction capture. Strain during processing can be as high as that during capture. In contrast, strain is compressive in the hyomandibula of skates during biting and ventilation, with greater strain when biting. It appears that major morphological shifts in the evolution of the jaw suspension and associated changes in kinematic patterns of the feeding apparatus also show related transformations in mechanical performance and feeding style. This also supports the theory that the jaw and hyoid arches evolved from branchial arches to increase ventilation performance and then became preadapted for feeding. This technique for measuring strain can be used on many biological structures for the broadest possible comparative content.
