Fig. 4

Schematic illustrating the hypothesized evolution of the chemical cueing and pheromone communication systems in sea lamprey. a larvae excrete 3-keto petromyzonol sulfate, or 3kPZS, and other chemicals as byproducts of metabolism; b migrating adults cue onto 3kPZS and other chemicals to locate habitat conducive to high-offspring survival; c males exploit the existing female preference for 3kPZS; d male release of 3kPZS continues to become exaggerated as a result of the fitness benefits associated with higher access to mates and female response to 3kPZS transitions from a non-targeted migratory response to a highly proximate spawning response.