Environment and Host Genetics Drive Infection Outcomes in a Butterfly Host, but Do Not Interact With Each Other

ABSTRACT

Understanding how host genetics and the environment interact to impact host resistance to parasite infection is crucial for predicting and controlling infectious diseases. Here we examined how different host families and environmental conditions (as provided by larval food plant) impact the probability of infection, infection burden, host lifespan, and size in a butterfly host. We used the monarch butterfly, Danaus plexippus , and two species of milkweed, Asclepias curassavica and A. incarnata , to examine the outcomes of different host genotypes (31 full‐sib families) in response to inoculation with a common and naturally occurring protozoan parasite, Ophryocystis elektroscirrha. We tested for the significance of genotype and environment (G × E) interaction effects, as well as the main effects of genotype and environment. We found that plant species affected infection status, infection burden, and host lifespan, and that host genetics impacted lifespan and wing length. However, our results indicated no G × E effects on any infection outcomes, indicating that larval diet and genetic effects operate independently in this system.