Data from: Loss of migratory behavior increases infection risk for a butterfly host

Long-distance animal migrations have important consequences for infectious
disease dynamics. In some cases, migration lowers pathogen transmission by
removing infected individuals during strenuous journeys and allowing
animals to periodically escape contaminated habitats. Human activities are
now causing some migratory animals to travel shorter distances or form
sedentary (non-migratory) populations. We focused on North American
monarch butterflies and a specialist protozoan parasite to investigate how
the loss of migratory behaviours affects pathogen spread and evolution.
Each autumn, monarchs migrate from breeding grounds in the eastern US and
Canada to wintering sites in central Mexico. However, some monarchs have
become non-migratory and breed year-round on exotic milkweed in the
southern US. We used field sampling, citizen science data and experimental
inoculations to quantify infection prevalence and parasite virulence among
migratory and sedentary populations. Infection prevalence was markedly
higher among sedentary monarchs compared with migratory monarchs,
indicating that diminished migration increases infection risk. Virulence
differed among parasite strains but was similar between migratory and
sedentary populations, potentially owing to high gene flow or insufficient
time for evolutionary divergence. More broadly, our findings suggest that
human activities that alter animal migrations can influence pathogen
dynamics, with implications for wildlife conservation and future disease
risks.