Dissertation Reserch: The Maintenance of a Genetic Color Polymorphism in the Mosquitofish, Gambushia Holbrooki

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9902312Travis & HorthThe goal of this project is to identify how a rare, genetically controlled, male body color pattern variant is maintained in many natural populations of mosquitofish, Gambusia holbrooki. This persistence is striking because males have only a single copy of the color-determining gene and theory suggests that this type of variation should not readily persist in nature. This study will address: (1) how water temperature may affect the expression of body color so as to mask the gene that causes melanism and make silver males appear more common than they really are; (2) how silver and melanic males interact with each other and with females; and (3) whether silver and melanic males differ in the number of offspring they sire when they compete for females, using behavioral observations and controlled genetic crosses. The study addresses a fundamental gap between theory and empirical pattern. In theory, single-copy genes, or haploids, ought not to exhibit much genetic variation in nature; in practice, variations like this one are common. It also addresses a novel feature of natural genetic variation, that of temperature-dependent expression and whether that expression is actually masking more genetic variation than is apparent. The way in which genetic variation is expressed in different thermal environments is a key issue in understanding how animals will respond to global change and whether that response will be merely ecological or also evolutionary. H:\popbio\abstracts\fy1999\9902312 (Travis abstract)