43rd ANNUAL DROSOPHILA RESEARCH CONFERENCE PROGRAM AND ABSTRACT VOLUME |
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13W Cytoplasmically inherited bacteria are common in insects. These bacteria have been named reproductive parasites because they often modify the reproduction of their hosts to benefit their own transmission. One of the most extreme cases of these bacterial manipulations is the induction of parthenogenesis by Wolbachia. Parthenogenesis inducing Wolbachia have been found in a large number of species of Hymenoptera and have been studied most intensively in parasitoid wasps. The mechanisms through which unfertilized eggs become females is gamete duplication, in which the first mitotic anaphase is aborted and the two mitotic sets of chromosomes fuse to become a single diploid nucleus. In hymenoptera, females are diploid, while males are haploid. In most cases the entire species or populations have become infected and only very few males are still present in the population. Once the infection has gone to fixation in the population the traits associated with sexual reproduction deteriorate. If males are produced through antibiotic treatment, the mating with females of their own population is generally unsuccessful. In only a few species the infection has not gone to fixation and only a part of the population is infected. In such populations mating takes place between infected females and uninfected males. In these populations strong conflicts genomic conflicts must exist between the nuclear wasp genes and those of the bacterium over control of the offspring sex ratio. These conflicts could result in the evolution of genes that suppress the Wolbachia or its effect. In at least one case a second selfish element, i.e., a B-chromosome that causes fertilized eggs to develop into males, has exploited the high frequency of infected virgin females. Its presence keeps the infection from going to fixation. |