Lack of genetic differentiation between monarch butterflies with divergent migration destinations

Abstract

Monarch butterflies are best known for their spectacular annual migration from eastern North America to Mexico. Monarchs also occur in the North American states west of the Rocky Mountains, from where they fly shorter distances to the California Coast. Whether eastern and western North American monarchs form one genetic population or are genetically differentiated remains hotly debated, and resolution of this debate is essential to understand monarch migration patterns and to protect this iconic insect species. We studied the genetic structure of North American migratory monarch populations, as well as nonmigratory populations in Hawaii and New Zealand. Our results show that eastern and western migratory monarchs form one admixed population and that monarchs from Hawaii and New Zealand have genetically diverged from North American butterflies. These findings suggest that eastern and western monarch butterflies maintain their divergent migrations despite genetic mixing. The finding that eastern and western monarchs form one genetic population also suggests that the conservation of overwintering sites in Mexico is crucial for the protection of monarchs in both eastern and western North America.

Serial founder effects and genetic differentiation during worldwide range expansion of monarch butterflies

“…Owing to the panmictic nature of the population in North America, our results provide a new outlook on monarch butterfly migration pathways. Results here also indicate that different migration strategies, such as the use of different overwintering sites or the presence of non-migratory behaviour, can be maintained between populations despite high levels of gene flow [38], as also seen in the admixed populations of migratory and sedentary groups of broad-tailed hummingbirds in North America [59]. A similar lack of neutral genetic differentiation has been observed in other highly mobile, migrating species, such as hoverflies with different overwintering strategies in France [60] and blackcaps with different migratory behaviours and destinations in Europe [61].…”

“…From North American migratory monarchs, we included samples from one fall migratory stopover site in north Florida (St Marks: 100 monarchs), two California overwintering sites (Pismo Beach and Santa Barbara: 100 monarchs) and two Mexico overwintering sites (Cerro Pelon and Sierra Chincua: 27 monarchs). We refer to the monarchs sampled from the eastern and western United States as the USA sample from hereon because despite overwintering in different locations, eastern and western North American monarchs are genetically indistinguishable on the basis of microsatellites [38]. We also included samples from non-migratory New World monarchs inhabiting South Florida, southern North America (Costa Rica and Belize), Caribbean and Atlantic islands (Puerto Rico and Bermuda) and South America (Ecuador and Aruba).…”

Non-target effects of clothianidin on monarch butterflies

“…Leaf tissue analysis The presence of clothianidin was tested in milkweed (Asclepias syriaca) plants that were a mean (SEM) 1.47±0.39 m from maize fields in Brookings County, SD, soon after maize planting (June 20, 2014; plants were 5-15 cm tall; n=8 sites), and when monarch populations were most abundant (July 25, 2014; n=10 sites; Lyons et al 2012). The late planting date in our area was the result of a very wet spring.…”

Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring

“…In general, monarchs east of the Rocky Mountains migrate to Mexico while monarchs west of the Rocky Mountains migrate to locations along the Pacific coast of California (Urquhart and Urquhart 1977), aggregating in groves of Monterey pine (Pinus radiata), Monterey cypress (Cupressus macrocarpa), and blue gum (Eucalyptus globulus) (Weiss et al 1991). Genetic studies have suggested that these populations are not distinct (Brower and Malcolm 1991;Lyons et al 2012;Zhan et al 2014), and some western monarchs potentially overwinter in Mexico (Dingle et al 2005;Morris et al 2015). Both populations depend on host plants in the genus Asclepias, the milkweeds.…”