Dr. Reginald B. Cocroft and Dr. Rafael L. Rodriguez University of Missouri-Columbia
Dr. Randy Hunt University of Indiana-Southeast
Plant-feeding insects constitute a large fraction of the earth's biological diversity. The formation of new species of plant-feeding insects may occur in the absence of geographic barriers to interbreeding between diverging populations (thought to be the usual mode of species formation). Under these conditions, new species can form if behavioral and ecological factors prevent individuals of one population from interbreeding. The research proposed here will examine this mode of diversification (called sympatric speciation) in a group of plant-feeding insects, the Enchenopa binotata species complex of treehoppers. The life cycle of E. binotata treehoppers is tightly linked with the growth cycle of their host plant. Females lay their eggs in late summer inside the stem and development in the spring is triggered by the movement of fluid inside the plant. When insects colonize a novel species of host plant with a different growth cycle, the populations on old and new hosts will differ in the timing of egg hatch and mating. These differences reduce interbreeding, but this partial isolation may not be sufficient for differentiation of the populations to occur. The recent discovery of substrate-borne vibrational mating signals that are transmitted through the plant tissue in E. binotata treehoppers suggests a factor that may complete isolation and lead to divergence (sympatric speciation). Mating in E. binotata occurs after a duet between a male and a female. Male signals consist of a tone about 1 sec long, followed by several short pulses. Females indicate receptivity to a particular male by alternating their own response signals with his. Males use female responses to locate them, and duets typically end in mating. Female responses thus provide an excellent assay of mate recognition. This project will characterize the mating signals, and female preferences for those signals, in the E. binotata complex. It will also examine the ways in which colonizing a new host plant can influence the mate communication system. This approach will help us understand the causes of diversity in mate communication systems, as well as the relationships between communication and biological diversity.
