Dissertation Research: Genetic Caste Determination in the Red Harvester Ant

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Colonies of the red harvester ant, Pogonomyrmex barbatus, consist of a single, multiply mated queen, and many sterile workers. Throughout her lifetime, the queen lays eggs that develop into workers, or reproductives, that is, males and virgin queens. In most social insects caste determination, whether an individual develops into a queen or a worker, is governed by environmental factors such as nutrition or incubation temperature of the eggs. However, our analyses of non-coding DNA regions called microsatellites revealed that in the red harvester ant, an individual's genotype predicts its caste. The proposed research will investigate how genetic caste determination affects a colony's development. The research will test whether queens that have mated with a single male, or multiple males of the same genotype, will have only males among their reproductives. Monitoring queens and genotyping their eggs will test whether eggs destined to become reproductives will not complete their development. This dissertation project will show how, under this unusual genetic system of caste determination, a colony can adjust the allocation of its resources to reproduction versus growth. This may reveal novel ways in which evolution by natural selection operates on colonies of social insects.