Symbiotic bacteria affect mating choice in Drosophila melanogaster

Mating preferences depending on Wolbachia infection were studied in two genotypically different strains of Drosophila melanogaster. Females from both strains carry two attached X chromosomes. Males from the red-eyed strain (R) have the wild-type X chromosome compared to males from the white-eyed strain (W), whose X chromosome contains two deleterious mutations (white and singed). Three types of competition tests showed that assortative mating depends on genotype, infection status and their combination in the mating partners. Males of strain R, genetically closer to the wild type, were more successful than males of strain W. Wolbachia infection increased the mating ability of W males but did not affect that of R males. Strain W showed positive assortative mating (preference for ‘self’) with regard to genotype and infection status. In strain R, negative assortative mating (preference for ‘nonself’) was observed. Moreover, the most affected flies (infected W) showed higher preference for ‘self’, while the least affected ones (uninfected R) showed higher preference for ‘nonself’. These results support the idea that mating choice may involve testing the partner for degree of genetic or biochemical similarity with self, based on chemoreception with possible participation of immune system components.