Spiroplasma effects on Tsetse Flies

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Tsetse flies are prominent vectors of pathogenic African trypanosomes, which cause socio- economically devastating diseases. Tsetse reproduce by adenotrophic viviparity and depend upon nutrients produced by their mutualist endosymbiont, Wigglesworthia. In addition to Wigglesworthia, some tsetse species can harbor parasitic Wolbachia and facultative Sodalis and Spiroplasma. Our studies on Wolbachia indicate that infection with the bacterium affects male reproductive physiology and induces Cytoplasmic Incompatibility. Here, we address the molecular dialogue between tsetse and its newly discovered endosymbiont Spiroplasma, which in other arthropods causes various reproductive abnormalities. Spiroplasma infects only tsetse species within the Palpalis subgenus, including Glossina fuscipes fuscipes (Gff), a prolific disease vector. Although its effects on tsetse reproduction are unknown, Spiroplasma induces enhanced resistance to trypanosome infection in the laboratory. We propose two research aims designed to dissect the impact of Spiroplasma infections on 1) male reproductive physiology related to mating success, 2) female fecundity, and 3) tsetse- Spiroplasma dialogue as it pertains to tsetse’s vector competence. Aim 1. Spiroplasma effects on male reproductive fitness. We hypothesize that Spiroplasma infections in male tsetse influence 1) MAG and testis gene expression, 2) spermatophore composition, and 3) sperm fitness. To test our hypothesis, we will 1) establish Spiroplasma infected and uninfected Gff lines, 2) perform comparative global gene expression analyses of gonads from Spi- versus Spi+ males, 3) determine spermatophore contents from the females mated with Spi- or Spi+ males, and 4) evaluate Spiroplasma effects on sperm fitness. Aim 2. Spiroplasma effects on parasite transmission dynamics. We hypothesize that Spiroplasma infections diminish tsetse’s vector competence 1) indirectly by a) inducing host immune responses or b) limiting nutrient availability for parasites, or 2) directly by expressing anti- trypanosomal products. To test our hypothesis, we will: 1) profile global gene expression from GffSpi- and GffSpi+ individuals, 2) determine nutritional status of trypanosome infected and uninfected GffSpi- and GffSpi+ individuals and 3) test cultivated Spiroplasma for trypanolytic activity. Enhanced knowledge about the tsetse-Spiroplasma symbiosis will provide a foundation to elucidate the mechanisms by which different reproductive endosymbionts influence host physiology. Our results will have translational implications, as reducing either tsetse fecundity or vector competence will directly reduce disease transmission. Finally, our results will be relevant and applicable to other medically and agriculturally important insects in which symbiotic microbes persist.