Spiroplasma impairs testes gene expression in Glossina fuscipes fuscipes

Glossina fuscipes fuscipes is a riverine tsetse fly species, the primary vector of human and animal trypanosomiasis in Sub-Saharan Africa. Controlling tsetse fly populations is crucial for mitigating the socio-economic impact of this disease, as effective treatments remain challenging. Indeed, the development of control strategies is hindered by the species' unique reproductive biology: adenotrophic viviparity, in which the female retains and nourishes the developing larva in her uterus throughout the pregnancy. The discovery of Spiroplasma in some G. f. fuscipes populations has drawn attention as a potential tool to enhance tsetse fly control strategies. Although Spiroplasma does not exhibit in G. f. fuscipes the male-killing phenotype observed in Drosophila melanogaster, evidence suggests that it may confer refractoriness to Trypanosoma infection. This has led to further investigations into its broader effects on G. f. fuscipes biology, particularly its potential impact on Glossina reproductive fitness. In this study, we considered Spiroplasma effect on the male reproduction. For this, we performed a differential gene expression analysis on testes and male accessory glands (MAGs) between Spiroplasma-infected and uninfected males. A significant downregulation of genes was observed in testes while a minor effect has been detected on MAGs. Downregulation of testes genes associated with functions related to sperm motility, energy metabolism, and mitochondrial function has been observed. Additionally, differentially expressed genes involved in antimicrobial activity and circadian rhythm regulation were observed. These findings provide valuable insights into the potential fitness costs of Spiroplasma infection for the fly and its implications for the bacterium use as biological control strategies targeting G. f. fuscipes.