Collaborative Research: The Evolution of Pheromone Signals and Their Role in Behavioral Isolation

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Collaborative Research: The Evolution of Pheromone Signals and their Role in Behavioral IsolationPI: Lynne D. Houck & Stevan Arnold and Richard C. Feldhoff & Pamela Feldhoff For millions of years, male terrestrial salamanders have executed a bizarre courtship that involves injecting females with pheromones. These courtship pheromones are protein signals that enhance the sexual receptivity of females. This example of reproductive communication has long been viewed as being shaped by sexual selection (via female mate choice) on the male signal. More recent evidence, however, implicates courtship pheromones as signals used by the female -not for mate choice- but for species identification. Thus, the evolution of this signaling system may be guided by mate recognition and behavioral isolation. We will use a well-developed study system to investigate whether male courtship pheromone signals affect behavioral isolation and hence speciation. We address two specific questions: (1) Do male courtship pheromone signals promote behavioral isolation? (2) What processes best explain the observed evolution of behavioral isolation? In the proposed work, we will focus on six population pairs showing different levels of behavioral isolation. We will experimentally manipulate chemical signals to test the hypothesis that male chemical signaling contributes to behavioral isolation. Secondly, we will use mathematical models to simulate the joint evolution of the male pheromone signal and female mating preferences across a group of related species. We will compare simulated data from each model with actual measures of behavioral isolation to determine which model gives the best fit. Our simulation methods will apply generally to any communication systems for which there are species of known relatedness and a survey of behavioral isolation between pairs of these species. In combination, our research will constitute a compelling case study of behavioral isolating mechanisms and how they evolve.