Intra-population variation in the natal origins and wing morphology of overwintering western monarch butterflies Danaus plexippus

et al. 1993, Wassenaar and Hobson 1998, Miller et al. 2010, 2012, Flockhart et al. 2013), while those that overwinter along the coast of California emerged from natal habitats west of the Rocky Mountains (Urquhart and Urquhart 1977, Nagano et al. 1993, Wenner and Harris 1993, Dingle et al. 2005, Stevens and Frey 2010). However, recent studies suggest that there may be significant interchange between the eastern and western populations (Brower and Pyle 2004, Dingle et al. 2005), consistent with the observation that these two populations are genetically panmictic at all tested loci (Shephard et al. 2002, Lyons et al. 2012). Although these populations have geographically distant (albeit climatically similar) overwintering grounds, the degree of overlap in their natal ranges remains unclear. Compared to the eastern population (Wassenaar and Hobson 1998, Miller et al. 2010, Flockhart et al. 2013), the natal origins of the western overwintering population remain surprisingly uncertain (Nagano et al. 1993, Wenner and Harris 1993, Dingle et al. 2005, Stevens and Frey 2010). Previous mark–recapture studies have documented the movement of wing-tagged monarch butterflies Ecography 38: 001–010, 2015 doi: 10.1111/ecog.01994 © 2015 The Authors. Ecography © 2015 Nordic Society Oikos Subject Editor: Erica Fleishman. Editor-in-Chief: Nathan J. Sanders. Accepted 12 November 2015