Hammerhead sharks are unique among extant elasmobranch species because of the presence of a laterally expanded and dorso-ventrally compressed head known as a cephalofoil. The shape of the cephalofoil varies greatly through sphyrnid phylogeny with basal species having the greatest lateral expansion (width 50% of total length) and derived species having the least later expansion (width 25% of total length). The changes of the cephalofoil through sphyrnid phylogeny are being investigated through the use of geometric morphometrics. Both landmark methods and outline methods will be used to determine how the cephalofoil and chondrocranium has changed through sphyrnid phylogeny. In conjunction with the shape change of the cephalofoil the anatomy of the feeding apparatus is being investigated to determine what affect the changing shape of the head has had on the functional morphology of the feeding apparatus. The kinematics of prey capture will also be investigated by filming live animal feeding events with a Redlake Motionscope high-speed digital video system and compared among species. The functional implications of the cephalofoil on sensory modality area are also being investigated. The laterally expanded cephalofoil provides more area for sensory modality areas such as electroreception. By comparing the areas devoted to different sensory modalities (ie electroreception, olfaction, vision, and mechanoreception) I will be able to determine the relationship between cephalofoil size/shape and sensory areas. This will allow me to compare how the area devoted to sensory modalities affects the feeding morphology. After all analyses have been completed, I will then be comparing the results to understand how the presence of a large planning surface at the front of the head has affected the feeding biology of hammerheads.

This research is being performed in collaboration with Steve Kajiura (Florida Atlantic University), Karl vonEllenrieder (Florida Atlantic University), and Andrew Martin (University of Colorado, Boulder). This collaborative research investigating the functional morphology, hydrodynamics, sensory biology, and evolution of the hammerhead cephalofoil is being funded by a grant from the National Science Foundation: "Collaborative Research: The function & evolution of the hammerhead shark cephalofoil." IOS-0640133.

The bonnethead shark is being used as model for studying the role of androgens (male sex steroid hormones) in elasmobranchs. This is a small crab-eating member of the hammerhead family (Sphyrnidae). The bonnethead is an abundant inshore species that can be maintained in captivity with ease making it a relatively convenient animal for study. Also adding to its appeal as a model for studies in reproductive physiology is the fact that the bonnethead’s reproductive and steroidal cycles have both been well-described. The goal of this project is to evaluate the expression patterns of androgen receptors (AR) both ontogenetically and seasonally in various reproductive tissues of male sharks. Molecular methods such as in situ hybridization and northern blotting will be utilized to evaluate the cellular location and relative levels of AR gene expression. Because elasmobranchs are the oldest living animals to possess an archetypical vertebrate pattern of reproductive endocrinology, this study may provide insight into the evolution of steroid hormone receptors.

Multisensory integration in shark feeding behaviors

Jayne Gardiner

The bonnethead is a small, abundant coastal species of hammerhead inhabiting inshore waters of the southeast U.S. coast.  Bonnetheads specialize on crustaceans such as small spiny lobster in the Florida Keys and small crabs along the southwest Florida coast (Cortes et al. 1996), using ram-biting almost exclusively (Wilga and Motta, 2000).  I am examining the striking preferences of intact animals as they are presented with spatially separate sources of olfactory, mechanical and electrical stimuli, as well as the effect of sensory lesions on the kinematics of the capture of live prey.  Due to their laterally expanded heads and widely spaced electrosensory pores (Kajiura and Holland, 2002), this species is expected to be an electrosensory specialist.