There is some amount of variation in almost every trait in every species that exists, and part of the cause of this variation is genetic. The well known forces of directional selection and genetic drift both act to reduce variation, so its maintenance is difficult to explain, and has been a long standing problem. The small marine crustacean, Paracercus sculpta has three different genetically based male body forms, which affect their ability to attract and mate with females. The proposed research will capitalize on this system to first identify the precise mode of inheritance, then describe how the environment influences the expression of the genotypes responsible for the different forms, and lastly attempt to account for the evolutionary forces that allow the three morphs to coexist. This system is uniquely suited to address these important questions, because the genotypes and the environments are easily manipulated, and the organism has a short generation time so that experiments can be done quickly. Furthermore, the answers should have broad generality for explaining the ubiquitous variation in nature.//
