9623487 Rissing Though species are often thought of as groups of organisms with similar traits, adaptation to local habitats can cause populations to vary in a wide variety of traits. Whether such variation can be maintained depends on the amount of migration between populations and the results of interactions between alternative forms in areas where populations contact one another, or hybrid zones. Research funded by this award addresses the maintenance of a behavioral hybrid zone for the desert seed-harvester ant, Messor pergandei. Seed harvester ants are keystone species, playing an important role in maintaining plant species diversity in desert systems. Queens of M. pergandei start colonies in two distinct ways. In the eastern half of the species' range, queens form groups and cooperate in nest construction. In the western half, queens are aggressive toward one another and dig solitary nests. This behavior switches over a 14 kilometer hybrid zone, within which both behaviors occur. To determine how this zone is maintained, the effects of queen density, hybridization and dispersal on colony founding rates and queen survival will be tested in controlled laboratory experiments. In addition, the importance of behavioral variation in determining rates of migration of genes between regions will be assessed in nature by documenting changes in frequencies of neutral genes across the hybrid zone. These two lines of evidence should give one of the first views of both the adaptive significance of behavioral diversity and its role in maintaining hybrid zones. Hybrid zones are continually in flux as new ones are established and existing ones eliminated by processes by environmental change. Rates of disappearance for hybrid zones however, have been exacerbated due to human disturbances. To understand the effects of human activity on population diversity, it is crucial to investigate the forces that act to maintain diversity in naturally occurring hybrid zones. The research funded in thi s award contributes to this goal.
