A study of the courtship song parameter in the 'Drosophila melanogaster' species complex

Abstract

Sexual isolation between populations has long been thought to play a role in speciation and evolution. However, the genetic control of factors causing sexual isolation is still not clearly understood. The interpulse interval (IPI) of the pulse song of the Drosophila melanogaster complex is important in female preference and species recognition. This thesis examined the genetic control of IPI. IPI may be important in the sexual isolation of species within the D. melanogaster complex, notably the three species D. melanogaster, D. simulans, and D. mauritiana. The genetic control of differences in IPI between D. simulans and D. mauritiana was studied using backcrosses and marker loci. The results showed that the control of the difference in IPI between species was evenly spread across five equally sized regions of the genome. Bi-directional artificial selection for shorter and longer IPI was carried out using replicate lines to control for genetic drift. The difference between selection regimes achieved was over 4.5 msecs. The difference was fixed using chromosome balancers to prevent recombination. Mating speeds of females from the selection lines with males from the selected and unselected lines were not significantly different from the original unselected stock following selection. The mean IPI of an African strain of D. melanogaster that had previously been shown to demonstrate premating isolation from other strains of D. melanogaster was measured, and was found to be significantly shorter than the control strain. Female mating speed of the African strain with males of the same strain was significantly faster than mating speeds with males of two strains with differing distributions for IPI. Heritability and evolvability of two song traits including IPI, and four morphological traits were measured in two generations of a strain recently derived from a wild population. All values were low, and mostly non-significant. The values for IPI were compared to values obtained from laboratory stocks, and with the values obtained for morphological traits. This study has furthered the understanding of the genetic control of IPI, and female response to changes in IPI. The examination of differences in IPI between populations and species remains important in our understanding of traits affecting sexual selection and premating isolation.