Loss of migratory behaviour increases infection risk for a butterfly host

Abstract

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.

Identifying Barriers to Citizen Scientist Retention When Measuring Pollination Services

“…Citizen science has proven useful in examinations of pollinator distributions and declines (Matteson et al 2012;Moskowitz and Haramaty 2013;Stafford et al 2010), responses to climate change (Breed et al 2012), population genetics (Harpur et al 2015), detection of exotic species (Ashcroft et al 2012;Wal et al 2015), nesting and hive properties (Graham et al 2014;Lye et al 2012;Sponsler and Johnson 2015), pesticide impacts (Muratet and Fontaine 2015), responses to habitat and landscape features (Bates et al 2014;Everaars et al 2011;Kremen et al 2011), migrations (Davis et al 2012Howard and Davis 2015;2009), overwintering (Howard et al 2010), disease dynamics (Satterfield et al 2015), and larval survivorship (Nail et al 2015).…”

Behavioural influences on disease risk: implications for conservation and management

“…If monarchs and their food sources are unable to make these distributional shifts, migrating populations of monarchs may be particularly at risk, leaving only populations that do not migrate, increasing the risk of parasite-induced population declines. Additionally, introduction of exotic milkweed, which provides year-round food for monarchs in the southern United States, has increased the number of nonmigratory populations, leading to increased infection prevalence (Satterfield, Maerz, & Altizer, 2015). Thus, human activities that reduce migration of monarchs may indirectly increase parasite prevalence in this host species.…”

Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host–parasite interactions

“…We estimated the fitness of uninfected and infected butterflies by measuring the lifespan of adults under constant temperature (128C), a standard procedure in this system [17,18,21,38]. Although we would prefer to measure fitness under more natural conditions, logistical constraints simply prohibit measuring individual butterfly fitness under natural conditions with the sample sizes required for our experiments.…”

“…This measurement, used routinely in this host -parasite system [17,18,21,38] combines longevity and starvation resistance, both of which are highly correlated with the lifespan and life-time fitness of monarchs under more natural conditions [17]. After death, the spore load of each butterfly was measured following described methods [17].…”