Morphological Variation in Olfactory, Optic, and Electrosensory Structures of Juvenile Scalloped Hammerhead Sharks (Sphyrna lewini )
Abstract
Though the variation in the design of the shark is vast, few iterations are as bizarre or recognizable as the hammerhead’s laterally expanded and dorsoventrally flattened heads, termed a “cephalofoil.” The uniqueness of this structure among sharks has led to many theories positing its purpose, for instance, that the laterally positioned eyes and nostrils allow for greater sampling ability (klinotaxis) in this family of sharks. In order to assess intra-specific variation of gross morphology, which would identify the conserved or the more variable features associated with sensory perception, the external features of the olfactory, optic and electro-sensory systems of scalloped hammerheads (Sphyrna lewini) were analyzed. Thirty-two juvenile scalloped hammerhead heads were obtained from Panamanian fishermen and photographed for ImageJ analysis. Principal component and multi-dimensional scaling analyses indicate an overall lack of variation between individuals, however, between the features measured there appears to be a high degree of similarity among those that maximize possible sampling area. This would seem to indicate that what variation does exist on the individual level is driven by prey acquisition. Additionally, ANOVAs of electroreceptor density indicate higher densities on the far lateral and far medial sections of the head, with lower densities in between. This could indicate a multi-step sensing approach used by S. lewini during prey capture, first employing the far-lateral sides of the head to corner prey, and then employing the central fields to make an accurate strike.
Degree
M.S.
Advisors
Paladino, Purdue University.
Subject Area
Biology
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