Jennifer Gleason

Sexual isolation- the reluctance of males and females of different species to mate with each other- can be a major cause of speciation in many animals. How many genes must change to produce sexual isolation? Some argue that species differences must involve change across many genes, perhaps hundreds, but the recent application of molecular techniques for gene mapping is suggesting, surprisingly, that single genes can play a large role in many ecologically important traits. Identification of genes affecting behavior is difficult; behavioral traits can be time consuming to measure and are prone to environmental influences. Although researchers have found mutations in single genes that affect behavior, it is not clear whether or not these genes are involve in variation within species or in species differences. In addition, most behaviors are quantitative traits and, therefore, must be influenced by multiple genes. For these reasons, I am using quantitative genetics to examine natural variation within and between species. Drosophila is an ideal model system for behavioral genetic analysis because the genetics of the organism are so well known and because it has reliably performed, quantifiable behaviors. My research uses two species that do not normally mate with each other. These species differ in female cuticular hydrocarbons (detected by the males) and male courtship songs (produced by wing vibrations and heard by females). Through quantitative trait loci analysis on backcross individuals, we can measure the cosegregation of these traits with molecular markers. Preliminary results indicate that songs are polygenic, but surprisingly are influenced by genes of major effect that are probably not those identified in single gene mutation analyses. Cuticular hydrocarbon composition is affected by one major locus, previously implicated, but other loci play a role in addition.