SULLIVAN, Laura E.*; COCROFT, Reginald B.; University of Missouri-Columbia; University of Missouri-Columbia: The influence of population density on mate-finding tactics and the strength of sexual selection in Enchenopa binotata treehoppers (Hemiptera: Membracidae)

Within species, mating systems and the strength of sexual selection will vary in time and space depending on variation in resource distribution, population density and operational sex ratio. In many cases, male mate-finding tactics vary in concert with these factors. However, the hypothesis that this variation in mate-finding tactics is adaptive has seldom been tested. We tested this hypothesis experimentally in a species in the Enchenopa binotata complex of treehoppers, which are small, sedentary, phloem-feeding insects. These treehoppers communicate with substrate-borne vibrational signals, and have two common mate-finding tactics: stationary chorusing and active searching. We manipulated the density of experimental populations, and then measured lifetime mating success of marked individuals whose mate-finding tactics were followed over the course of the mating season. We released the treehoppers into large outdoor enclosures to create high-density (40 males/40 females) and low-density (10 males/10 females) conditions. We marked individuals to track their movements and mating behavior. The location and behavior (including courtships and matings) of each treehopper was recorded every 90 minutes during daylight hours. The movements of the males were used to categorize their mate-finding tactics as either chorusing or active searching. Our results suggest that there is a large opportunity for sexual selection in this species. The influence of population density on the strength of sexual selection and on the fitness payoffs of different male mate searching tactics will be discussed.