Understanding how shifts from migratory to sedentary behavior influence pathogen dynamics in butterfly host
Satterfield, Dara Ashley
MetadataShow full item record
Seasonal animal migrations can have profound ecological consequences, including for infectious disease dynamics. Migration can often lower infection risk, if animals escape from parasite-contaminated habitats or if strenuous journeys cull infected hosts. Many migratory species are now undergoing shifts or declines in migration. Numerous animal species have responded to environmental changes by forming sedentary populations that remain in the same location. My doctoral research explores how the break-down of animal migrations alters pathogen transmission. Two driving questions guide this work: (1) Do sedentary populations that forego migration face greater infection risk compared to migratory conspecific populations? (2) Do sedentary populations affect the behavior and infection risk of remaining migratory animals? We focused on monarch butterflies (Danaus plexippus) and their protozoan parasite (Ophryocystis elektroscirrha, OE) as a model system. Most monarchs in North America migrate annually to overwintering areas in Mexico and California, and this journey reduces OE prevalence. In parts of the U.S., however, some monarchs now breed year-round on an exotic milkweed species planted in gardens. We collaborated with citizen scientists to test over 9000 wild monarchs for parasites. Results showed that, relative to migratory butterflies, sedentary monarchs experienced 5- to 9-fold higher infection risk at year-round breeding sites. We next developed a mathematical model to examine host-parasite dynamics at a much smaller scale, within a milkweed patch. Our model indicated that OE spore persistence in the environment led to rising prevalence within a breeding season. This could be particularly important at sedentary sites, where breeding is continuous. Finally, we evaluated potential impacts of sedentary monarchs on migrants, using chemical analyses to distinguish natal origins of wild butterflies. We found that migratory monarchs share habitat with parasitized resident monarchs in the fall and spring in coastal Texas. Migrants sampled at year-round breeding sites showed a greater probability of having OE infections and reproductive activity – both factors that are known to decrease migratory success. Collectively, our findings suggest that human activities that alter animal migrations can influence pathogen dynamics. For this butterfly species, native and seasonal milkweeds (rather than exotic, year-round species) could better support monarch migration and health.