The role of two anatomically separate olfactory bulbs in shark food odor tracking
MetadataShow full item record
Most sharks have well-developed olfactory systems and depend to a large degree on odor information to locate food, home and navigate, and possibly detect predators and mates. The aim of this investigation is to determine the behavioral function of two paired bilateral olfactory bulbs in the smooth dogfish shark, Mustelus canis. The paired olfactory bulbs are a rare and unique feature among elasmobranchs and are absent in bony fishes. Given that the olfactory system of bony fishes contains lateral and medial nerve bundles with behavioral functions in feeding and social behavior respectively, we hypothesize that sharks have an elaborate functional division in which the medial bulb is processing social odors and the lateral bulb food odors. This functional division would parallel the division into an olfactory and an accessory olfactory system, also known as the vomeronasal organ or Jacobson’s organ, which evolved in tetrapods. Our study is based on the behavioral effects of selective transection of the two olfactory tracts to reveal how the brain is processing input from two anatomically distinct olfactory systems. The results show that animals with lateral tract transections showed impaired ability to track a food odor plume while those with medial transections showed no change. Attempts to identify a reliable social odor (pheromone) were not successful, preventing us from determining the deficits expected from medial tract lesions.