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

Range expansions can result in founder effects, increasing genetic
differentiation between expanding populations and reducing genetic
diversity along the expansion front. However, few studies have addressed
these effects in long-distance migratory species, for which high dispersal
ability might counter the effects of genetic drift. Monarchs (Danaus
plexippus) are best known for undertaking a long-distance annual migration
in North America, but have also dispersed around the world to form
populations that do not migrate or travel only short distances. Here, we
used microsatellite markers to assess genetic differentiation among 18
monarch populations and to determine worldwide colonization routes. Our
results indicate that North American monarch populations connected by land
show limited differentiation, probably because of the monarch's
ability to migrate long distances. Conversely, we found high genetic
differentiation between populations separated by large bodies of water.
Moreover, we show evidence for serial founder effects across the Pacific,
suggesting stepwise dispersal from a North American origin. These findings
demonstrate that genetic drift played a major role in shaping allele
frequencies and created genetic differentiation among newly formed
populations. Thus, range expansion can give rise to genetic
differentiation and declines in genetic diversity, even in highly mobile
species.