Monarch butterflies cross the Appalachians from the west to recolonize the east coast of North America

Abstract

Each spring, millions of monarch butterflies (Danaus plexippus) migrate from overwintering sites in Mexico to recolonize eastern North America. However, few monarchs are found along the east coast of the USA until mid-summer. Brower (Brower, L. P. 1996 J. Exp. Biol. 199,[93][94][95][96][97][98][99][100][101][102][103] proposed that east coast recolonization is accomplished by individuals migrating from the west over the Appalachians, but to date no evidence exists to support this hypothesis. We used hydrogen (dD) and carbon (d 13 C) stable isotope measurements to estimate natal origins of 90 monarchs sampled from 17 sites along the eastern United States coast. We found the majority of monarchs (88%) originated in the mid-west and Great Lakes regions, providing, to our knowledge, the first direct evidence that second generation monarchs born in June complete a (trans-) longitudinal migration across the Appalachian mountains. The remaining individuals (12%) originated from parents that migrated directly from the Gulf coast during early spring. Our results provide evidence of a west to east longitudinal migration and provide additional rationale for conserving east coast populations by identifying breeding sources.

Butterfly response to floral resources during early establishment at a heterogeneous prairie biomass production site in Iowa, USA

“…The availability of abundant nectar sources throughout the growing season in our biomass production plots sharply contrasts the habitat conditions found in corn and soy fields, and the consistent seasonal availability of high quality nectar sources may support D. plexippus at critical times during its complex migratory cycle. For example, abundant nectar sources in June and early July support breeding individuals whose offspring later colonize the eastern USA (Miller et al 2011), and nectar sources in August and September allow migrating individuals to accumulate sufficient lipid stores to survive the overwintering period in Mexico (Brower et al 2006). While the degree to which agricultural intensification and the consequent reduction in forbs is currently affecting D. plexippus populations is unclear (Brower et al 2006), our observations suggest that implementation of biomass production systems using diverse mixes of native species on marginal lands could provide abundant nectar sources and improved habitat conditions for D. plexippus and other generalist nectar-feeding butterflies.…”

Migration distance as a selective episode for wing morphology in a migratory insect

“…Details of probabilistic assignment of natal origin are found in [32] but we briefly summarize the approach below. We used multivariate normal distribution assignment models to calculate the probability of natal origin to each pixel in a continuous landscape that spans the monarch breeding distribution [34, 36, 41]. For each butterfly, the model calculated the probability of natal origin to each pixel in our study area based on the correspondence between δ 2 H and δ 13 C values in wing tissue to the isoscape-predicted values of monarch δ 2 H and δ 13 C wing tissue of each geographically indexed cell in the landscape [42].…”

“…To examine this hypothesis, we estimated migration distance of overwintering monarchs in Mexico sampled over five decades by estimating natal origin from two stable isotopes ( δ 13 C and δ 2 H) in their wing tissue [22, 34–36]. Given that last generation monarchs in eastern North America migrate directly to a few spatially clustered locations in central Mexico [37], fall migration distance and ambient temperature experienced during larval development can be estimated as a direct function of natal origin in eastern North America.…”

Enhancing Monarch Butterfly Reproduction by Mowing Fields of Common Milkweed

“…in Mexico, return the following spring to the southern United States, and establish a new generation by laying their eggs on milkweeds of the genus Asclepias. This first spring generation then continues the migration northeasterly into the midwestern and northeastern states, where two or more additional generations develop over the spring and summer (Malcolm et al, 1993;Brower, 1995;Howard and Davis, 2004;Miller et al, 2011). The monarch migration has been designated an endangered biological phenomenon (Brower and Malcolm, 1991) in which the species as a whole may not be in jeopardy, but a major aspect of its biology, the migration of the entire eastern North American population to one small area in Mexico, is at risk.…”