Migratory Connectivity of the Monarch Butterfly (Danaus plexippus): Patterns of Spring Re-Colonization in Eastern North America

Abstract

Each year, millions of monarch butterflies (Danaus plexippus) migrate up to 3000 km from their overwintering grounds in central Mexico to breed in eastern North America. Malcolm et al. (1993) articulated two non-mutually exclusive hypotheses to explain how Monarchs re-colonize North America each spring. The ‘successive brood’ hypothesis proposes that monarchs migrate from Mexico to the Gulf Coast, lay eggs and die, leaving northern re-colonization of the breeding range to subsequent generations. The ‘single sweep’ hypothesis proposes that overwintering monarchs continue to migrate northward after arriving on the Gulf coast and may reach the northern portion of the breeding range, laying eggs along the way. To examine these hypotheses, we sampled monarchs throughout the northern breeding range and combined stable-hydrogen isotopes (δD) to estimate natal origin with wing wear scores to differentiate between individuals born in the current vs. previous year. Similar to Malcolm et al. (1993), we found that the majority of the northern breeding range was re-colonized by the first generation of monarchs (90%). We also estimated that a small number of individuals (10%) originated directly from Mexico and, therefore adopted a sweep strategy. Contrary to Malcolm et al. (1993), we found that 62% of monarchs sampled in the Great Lakes originated from the Central U.S., suggesting that this region is important for sustaining production in the northern breeding areas. Our results provide new evidence of re-colonization patterns in monarchs and contribute important information towards identifying productive breeding regions of this unique migratory insect.

Tracking multi-generational colonization of the breeding grounds by monarch butterflies in eastern North America

“…Similar to previous studies, our data were collected in one year, preventing us from addressing the factors that may influence interannual variation in movement rates. However, our results agree with Malcolm et al [4] and Miller et al [18], who studied the relative proportion of individuals moving between the Gulf Coast and the Great Lakes during spring in different years. Overall, annual variation in movement rates is probably driven by climate and weather [9] with warmer years predicted to have increased northward expansion [25].…”

“…In this study, we described connectivity throughout the entire breeding season and sampled monarchs across the entire eastern breeding range. In doing so, we addressed three long-standing questions in monarch breeding biology: (i) does movement into northern breeding areas continue throughout the breeding season or is there a single re-colonization pulse into northern breeding distributions in early summer followed by local recruitment [4,18,19]? (ii) is the re-colonization of southern areas during early autumn a result of local or long-distance dispersal [20,21]?…”

Within-wing isotopic (δ2H, δ13C, δ15N) variation of monarch butterflies: implications for studies of migratory origins and diet

“…Stable-carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios in particular have been used to investigate dietary inputs, sources of feeding and trophic positions of a broad spectrum of taxa (Kelly 2000, Inger and Bearhop 2008, Hobson 2011, Hyodo 2015. More recently, measurements of stable hydrogen isotope ratios (δ 2 H) have been used successfully to infer origins in numerous species of migratory birds and insects (Hobson and Wassenaar 2008, Hobson et al 2012, Stefanescu et al 2016. Among insects, the greatest focus has been on tracing origins and movements of the eastern North American population of monarch butterflies (Danaus plexippus).…”

Variation in Forewing Size Linked to Migratory Status in Monarch Butterflies

“…While many animals acquire migratory behaviors through learning [4], this is not the case for monarch butterflies. A migration cycle is complete after a monarch butterfly travels to Mexico and 3-4 generations of its offspring make the return trip back north [17]. Therefore, because multiple generations separate each migration event, the migratory behavior in monarchs is innate.…”