Low sex drive and choosy females: Fungal infections are a reproductive downfall for male house flies

Many entomopathogenic fungi cause infections that kill their insect host.
Little is understood about changes in the reproductive investment that
occur during an infection by a lethal disease over the waning life of an
insect. Life history theory suggests the host will respond by investing
resources into fighting the disease or increasing reproduction. Here, we
investigate how the reproductive life of adult house flies, Musca
domestica, is impacted by its host-specific fungal pathogen, Entomophthora
muscae. Specifically, we test how the week-long infection alters the
mating behavior of virgin adult male house flies. We find that the
pathogen significantly decreases male libido; an effect which grows
stronger over the course of the infection. Furthermore, females were
significantly less likely to choose an infected male, reducing male mating
success. Additionally, we assessed sperm viability to understand the
reproductive costs for monandrous females to mate with infected males.
Analyses revealed that sperm quality decreases as early as three days
post-infection. These results show that E. muscae, which can have a
prevalence near 100% in wild populations, causes severe lifetime
reproductive costs to male house flies. Understanding how host-pathogen
interactions affect host life history is crucial for elucidating all the
negative effects pathogen virulence exerts on hosts.