Documenting successful recruitment of monarch butterflies (Lepidoptera: Nymphalidae) at the extreme northern edge of their range D.T. Tyler Flockhart, 1 John H. Acorn, Keith A. Hobson, D. Ryan Norris Abstract—Monarch butterflies (Danaus plexippus (Linnaeus) (Lepidoptera: Nymphalidae)) in eastern North America migrate each year from overwintering areas in Mexico to cover a large breeding distribution across the United States of America and southern Canada. In 2012, monarch butterflies migrated well beyond their usual range, resulting in an extended breeding distribution compared to typical years. We used stable isotope (δ 2 H, δ 13 C) measurements in wing chitin to determine the area of natal origin of these butterflies. Most monarch butterflies collected in May, June, and July from Manitoba and Alberta, Canada had natal origins in the North American Midwest. Monarch butterflies collected in Alberta and Saskatchewan, Canada in August and September had local natal origins indicating successful recruitment of offspring from colonising individuals. However, it is unknown whether these offspring migrated successfully to overwintering areas. Our work highlights the ability of monarch butterflies to colonise distant breeding areas and demonstrates how stable isotopes can be used to understand the dynamics of range-edge populations. Introduction Many multivoltine migratory insects expand their ranges annually to cover large breeding distributions (Chapman et al. 2015; Stefanescu et al. 2016). Mass-movements of butterflies (Lepidoptera), moths (Lepidoptera), locusts (Orthoptera: Acrididae), and other insects are often aided by weather systems that promote long-distance movement (Chapman et al. 2015; Hu et al. 2016) and facilitate successful breeding in distant breeding habitats (Chapman et al. 2012). Global climate change could result in changes to host-plant distributions (e.g., Lemoine 2015), which might negatively impact less-mobile habitat specialists (Warren et al. 2001) but benefit mobile specialists such as migratory butterflies (Batalden et al. 2007). To track such movements, it is essential to determine the origins of immigrant individuals (Hobson et al. 2018) and whether they successfully recruit offspring into the population once they have arrived in a new area (McNeil 1978; Chapman et al. 2012). Determining the area of origin of individual butterflies can be accomplished using intrinsic markers such as stable isotopes (Rubenstein and Hobson 2004). Stable isotopes are powerful tools for assigning natal origins for monarch butterflies (Danaus plexippus (Linnaeus) (Lepidoptera: Nymphalidae)) because isotopic ratios are typically transferred in a predictable fashion trophically in food webs and are ultimately retained in wing tissue of insects (Hobson et al. 1999; Flockhart et al. 2015). In North America, stable-hydrogen isotopes in precipitation vary predictably across latitudinal gradients (Hobson et al. 1999; Terzer et al. 2013), whereas stable-carbon isotopes in milkweed (Asclepias Linnaeus; Apocynaceae) vary dependent D.T.T. Flockhart, 1 Department of Integrative Biology, Summerlee Science Complex, University of Guelph, Guelph, Ontario, N1G 2W1, Canada; and University of Maryland Center for Environmental Science Appalachian Laboratory, 301 Braddock Road, Frostburg, Maryland, 21532, United States of America J.H. Acorn, Department of Renewable Resources, University of Alberta, 751 General Services Building, Edmonton, Alberta, T6G 2H1, Canada K.A. Hobson, Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada S7N 3H5; and Department of Biology, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada D.R. Norris, Department of Integrative Biology, Summerlee Science Complex, University of Guelph, Guelph, Ontario, N1G 2W1, Canada 1 Corresponding author (e-mail: tyler.flockhart@umces.edu) Subject editor: Cory Sheffield doi:10.4039/tce.2018.52 Received 23 March 2018. Accepted 11 July 2018. First published online 6 November 2018. Can. Entomol. 151: 49–57 (2019) © 2018 Entomological Society of Canada 49 https://www.cambridge.org/core/terms. https://doi.org/10.4039/tce.2018.52 Downloaded from https://www.cambridge.org/core. University of Guelph Library, on 08 Mar 2019 at 19:57:50, subject to the Cambridge Core terms of use, available at