Meeting Abstract
Variability in the size and complexity of the brain and its major regions in cartilaginous fishes is often associated with habitat and/or specific behavior patterns, providing a link between brain form and specialized function. The Greenland (Somniosus microcephalus) and Pacific sleeper (S. pacificus) sharks are two of only a few shark species known to occur in the Arctic and are among the longest living vertebrates ever described, though many aspects of their behavior, life history, and basic biology remain poorly understood. Among the most distinctive characteristic of Somniosus spp. is the presence of ocular lesions. Despite a presumed visual impairment caused by this parasite, coupled with the fact that locomotory muscle power is often depressed at cold temperatures, these sharks remain capable of capturing active prey, including pinnipeds. Therefore, the central nervous system of these two unique shark species was examined as a way of predicting the relative importance of different sensory modalities in predatory behavior. Using magnetic resonance imaging, we assessed relative brain size and brain organization of S. microcephalus and S. pacificus in the context of a broad range of other shark species (n=117). Notably, the region of the brain responsible for motor control (cerebellum) is small and lacking in foliation. Further, the development of visual brain regions are relatively reduced, while the olfactory brain regions are among the largest of any shark species described to date, suggestive of an olfactory-mediated prey tracking behavior in a slow moving predator.
