Patterns of parasitism in monarch butterflies during the breeding season in eastern North America

Abstract

Abstract. 1. Migratory behaviour can result in reduced prevalence of pathogens in host populations. Two hypotheses have been proposed to explain this relationship: (i) 'migratory escape', where migrants benefit from escaping pathogen accumulation in contaminated environments; and (ii) 'migratory culling', where the selective removal of infected individuals occurs during migration.2. In the host-parasite system between the monarch butterfly (Danaus plexippus Linn.) and its obligate protozoan parasite Ophryocystis elektroscirrha (OE), there is evidence to support both hypotheses, particularly during the monarchs' autumn migration. However, these processes can operate simultaneously and could vary throughout the monarchs' annual migratory cycle. Assessing the relative strength for each hypothesis has not previously been done.3. To evaluate both hypotheses, parasite infection prevalence was examined in monarchs sampled in eastern North America during April-September, and stable isotopes ( 2 H, 13 C) were used to estimate natal origin and infer migration distance. There was stronger support for the migratory escape hypothesis, wherein infection prevalence increased over the breeding season and was higher at southern latitudes, where the breeding season tends to be longer compared with northern latitudes. Little support was found for the migratory culling hypothesis, as infection prevalence was similar whether monarchs travelled shorter or longer distances.4. These results suggest that migration allows individuals to escape parasites not only during the autumn, as shown in previous work, but during the monarchs' spring and summer movements when they recolonise the breeding range. These results imply a potential fitness advantage to monarchs that migrate further north to exploit parasite-free habitats.

Mechanisms and Consequences of Partial Migration in Insects

“…However, the role of trophic interactions has received relatively little attention in the partial migration literature (Chapman et al, 2011) and has rarely been studied in migratory insects (Altizer et al, 2011;Chapman et al, 2015). Nonetheless, there is evidence that migration can reduce the prevalence of infection from the protozoan parasite, Ophryocystis elektroscirrha in monarchs (Bartel et al, 2011;Altizer et al, 2015;Flockhart et al, 2018), with resident populations having higher infection rates than migrant populations (Satterfield et al, 2015(Satterfield et al, , 2016(Satterfield et al, , 2018, providing evidence of "migratory escape" (Altizer et al, 2011) from contaminated environments.…”

Migratory monarchs that encounter resident monarchs show life‐history differences and higher rates of parasite infection

“…; Flockhart et al . ). However, some monarchs now breed year‐round in the southern US and do not migrate (Howard et al .…”

Inferring origins of migrating insects using isoscapes: a case study using the true armyworm, Mythimna unipuncta, in North America

“…Larger-scale movements of insects are now being investigated using stable hydrogen isotopes ( 2 H) in metabolically inert tissues such as wings and comparing those with continent-wide patterns expected from 2 H of amount-weighted mean growing season precipitation 2 H ( 2 H p ; Hobson & Wassenaar, 2008). For example, employing continental patterns, or 'isoscapes' (West et al, 2010), of both precipitation 2 H and milkweed 13 C, together with the isotopic values in wings of monarch butterflies (Danaus plexippus Linnaeus), this approach has been used to: (i) trace the origins and movements in eastern North America (Wassenaar & Hobson, 1998;Hobson et al, 1999); as well as to infer (ii) patterns of spring recolonisation in eastern North America (Miller et al, 2012;Flockhart et al, 2013); (iii) the origins of wintering individuals in western North America (Yang et al, 2016); (iv) the effects of natal origin on parasite loads (Altizer et al, 2015); (v) the role of wing coloration in flight distance (Hanley et al, 2013); and (vi) general conservation concerns related to areas of high productivity (Flockhart et al, 2017;Flockhart et al, 2018). Similar large-scale tracking studies using naturally occurring stable isotopes have been used to examine the movement of the red admiral (Vanessa atalanta Fruhstorfer) and painted lady (V. cardui Linnaeus) butterflies in Europe and sub-Saharan Africa (Brattström et al, 2010;Stefanescu et al, 2016), as well as the globe skimmer (Pantala flavescens Fabricius) dragonfly from India across the Indian Ocean (2012).…”