The chemical ecology and potential application of the sea lamprey migratory pheromone

A variety of studies has established that migratory adult sea lampreys (Petromyzon marinus) locate rivers for spawning using a potent bile acid-derived pheromone released by larval conspecifics and perhaps other lamprey species. Adult sea lampreys are caught in the greatest numbers in those tributaries of the Great Lakes which contain large populations of larval sea lamprey, and removing larvae from these tributaries makes them less attractive than neighboring rivers which still have larvae. Stream selection appears to be mediated by odorous cues because occluding the olfactory systems of adults severely reduces their ability to locate streams. Experiments using laboratory mazes confirm that adult sea lampreys are attracted to very low dilutions of stream water, especially when it is collected from streams that contain larval lamprey. Tests of larval holding water find it to be highly attractive and suggest that a single larva activates almost 4,000 L of river water an hour. Finally, biochemical studies combined with electrophysiological recording from the sea lamprey olfactory system and behavioral experiments demonstrate that the migratory pheromone released by larvae is comprised of the unique lamprey bile acid, petromyzonol sulfate and at least one unknown compound. The precise importance of this mixture and its specific role(s) in mediating stream finding behavior and upstream migration has yet to be resolved. Together, these studies demonstrate that this pheromone is a potent stimulant of adult sea lamprey migratory behavior which might be useful in sea lamprey control. Three possibilities for its use in streams as well as six pheromone formulations are discussed.