Monarch butterfly migration and parasite transmission in eastern North America

Abstract

Abstract. Seasonal migration occurs in many animal systems and is likely to influence interactions between animals and their parasites. Here, we focus on monarch butterflies (Danaus plexippus) and a protozoan parasite (Ophryocystis elektroscirrha) to investigate how host migration affects infectious disease processes. Previous work showed that parasite prevalence was lower among migratory than nonmigratory monarch populations; two explanations for this pattern are that (1) migration allows animals to periodically escape contaminated habitats (i.e., migratory escape), and (2) long-distance migration weeds out infected animals (i.e., migratory culling). We combined field-sampling and analysis of citizen science data to examine spatiotemporal trends of parasite prevalence and evaluate evidence for these two mechanisms. Analysis of within-breeding-season variation in eastern North America showed that parasite prevalence increased from early to late in the breeding season, consistent with the hypothesis of migratory escape. Prevalence was also positively related to monarch breeding activity, as indexed by larval density. Among adult monarchs captured at different points along the east coast fall migratory flyway, parasite prevalence declined as monarchs progressed southward, consistent with the hypothesis of migratory culling. Parasite prevalence was also lower among monarchs sampled at two overwintering sites in Mexico than among monarchs sampled during the summer breeding period. Collectively, these results indicate that seasonal migration can affect parasite transmission in wild animal populations, with implications for predicting disease risks for species with threatened migrations.

Seasonal migration to high latitudes results in major reproductive benefits in an insect

“…Just how representative A. gamma is of other migrant insects is a matter for future study, but given the similarities in the migration strategies of A. gamma to those of other insects in Europe (24,34), Asia (21), North America (3,5,19,20), and Australia (8,35), it is very likely that the results of the present study will be applicable to a wide range of migrants. We conjecture, therefore, that during a time when most sedentary Lepidoptera (36,37) and many migrant birds (38,39) have experienced dramatic declines, the shared traits of high fecundity (40), polyphagy (26), year-round breeding (26), reduced disease and parasite loads (41,42), and efficient strategies for the use of windborne transport (43) to exploit widely dispersed seasonal resources are the principal factors that have enabled the recent temperature-related range expansions and population increases observed in many species of migrant Lepidoptera (44). Considering the pest status of A. gamma (and many other species of migrant moths), which is facilitated by their polyphagy, it is certainly germane to increase our understanding of the migration systems of such species.…”

Assessing Role of Major Drivers in Recent Decline of Monarch Butterfly Population in North America

“…For example, Bartel et al (2011) demonstrated that the monarch protozoan parasite Ophryocystis elektroscirrha prevalence increased during the host breeding season. However, it was also determined that monarchs sampled at two overwintering sites in Mexico had lower parasite prevalence than those sampled at summer breeding sites (Bartel et al, 2011).…”

“…For example, Bartel et al (2011) demonstrated that the monarch protozoan parasite Ophryocystis elektroscirrha prevalence increased during the host breeding season. However, it was also determined that monarchs sampled at two overwintering sites in Mexico had lower parasite prevalence than those sampled at summer breeding sites (Bartel et al, 2011). Similarly, Altizer et al (2000) determined that non-migratory monarchs in southern Florida that continuously breed were over 70% parasite infested, while Western monarchs that migrate moderate distances to overwintering sites were 30% parasite infested and Eastern monarchs that migrate to Mexico were less than 8% parasite infested over a 30-year timespan.…”

Butterfly Citizen Science Projects Support Conservation Activities among their Volunteers

“…Global climate change, habitat loss owing to development and pesticide-induced loss of host and nectar plants, and disease all have been suggested as threats to butterfly populations (e.g., McLaughlin et al 2002;Bartel et al 2011;Preston et al 2012;Pleasants and Oberhauser 2013). These issues are not unique to butterflies.…”