Wolbachia pipientis is a bacterial cytoplasmic symbiont common in arthropods and nematodes. The form of Wolbachia that has the ability to induce parthenogenesis in its host (parthenogenesis-induction, PI) effectively feminizes male embryos and allows infected females to reproduce without mating (parthenogenesis). Most of the haplodiploid species infected with PI-Wolbachia have lost the ability to reproduce sexually, resulting in clonal lineages dependent upon Wolbachia for reproductive survival. Trichogramma kaykai, a hymenopteran parasitoid native to the Mojave Desert, is one of the few species where PI-Wolbachia circulates within populations, yet infected females are still capable of reproducing sexually. We use this unique T. kaykai/Wolbachia symbiosis to investigate the fitness consequences of PI Wolbachia infection and the related loss of genetic variation associated with parthenogenesis. A mating scheme was developed with infected and cured T. kaykai cultures that had been isolated as isofemale lineages for over 400 generations. Utilizing the retained sexual function of infected T. kaykai we were able to introduce genetic variation in both infected and cured experimental cultures to test the hypothesis of increased fitness with genetic variation. Our results suggest there are significant costs associated with infection and absence of genetic recombination. These results are discussed in terms of ecological conditions and evolutionary consequences for Wolbachia-infected populations.
