THE EVOLUTION OF CHEMICAL ALARM SIGNALS - ATTRACTING PREDATORS BENEFITS ALARM SIGNAL SENDERS

A wide variety of organisms possess damage-released alarm pheromones t hat evoke antipredator responses in conspecifics. Understanding the ev olution of such involuntary alarm signals has been perplexing because it is difficult to see direct benefits to the sender, notwithstanding benefits derived from warning relatives. Recently, it has been propose d that the alarm pheromone, or Schreckstoff, of Ostariophysan fishes m ay function in a fashion analogous to distress calls of many birds and mammals. The alarm pheromone may attract secondary predators to the p roximity of the primary predation event, and, once there, the secondar y predators may disrupt the predation event, thus allowing the prey gr eater opportunity to escape. Previous findings have established that t he alarm pheromone of fathead minnows (Pimephales promelas) attracts p redators, including northern pike (Esox lucius) to an area. In this st udy we demonstrate that the probability that fathead minnows will esca pe after being captured by a northern pike is significantly increased through interference by a second pike. Taken with the previous finding s that alarm pheromone attracts predators, these results are the first to provide empirical evidence of benefits to senders of an involuntar y alarm signal.