Repellent function of male pheromones in the red-spotted newt

Pheromones act as attractants and sexual stimulants in most vertebrates. Fo r example, in red-spotted newts, Notophthalmus viridescens, female pheromon es attract males, and male pheromones increase female receptivity. However, no studies have det;ermined whether male vertebrates produce a pheromone t hat repels competing males. Through a series of olfactory mate selection te sts, we found that sexually motivated male red-spotted newts produce a pher omone that functions to repel other approaching males. Our finding is the f irst report of a repelling function for pheromones in male vertebrates. The pheromones may act to increase both the sender's and receiver's mating suc cess when the operational sex ratio (OSR) is male biased. J. Exp. Zool. 289 :404-408, 2001. (C) 2001 Wiley-Liss, Inc.