Interactions between parasitism and migration in monarch butterflies

In many species, migration can increase parasite burdens or diversity as hosts move between diverse habitats with different parasite assemblages. On the other hand, migration can reduce parasite prevalence by letting animals escape infested habitats, or by exacerbating the costs of parasitism, leading to culling or dropout. How the balance between these negative and positive interactions is maintained or how they will change under anthropogenic pressure remains poorly understood. Here, we summarize the relationship between migration and infectious disease in monarch butterflies, finding that migration can reduce parasite prevalence through a combination of migratory culling and dropout. Because parasite prevalence has risen in recent decades, these processes are now resulting in the loss of tens of millions of monarchs. We highlight the remaining questions, asking how migration influences population genetics and virulence, how the establishment of resident populations interferes with migration, and whether infection can interfere with migratory cognition.

Automated summary

In many species, migration can either increase or reduce parasite prevalence depending on migratory culling and dropout. The relationship between migration and infectious disease in monarch butterflies has been investigated, and it was found that migration can decrease parasite prevalence resulting in the loss of millions of monarchs. The remaining questions highlight the influence of migration on genetics, the interference of resident populations with migration, and the impact of infection on migratory cognition.