A broadly distributed migratory butterfly travels varying distances, influenced by environmental conditions rather than following genetically coded instructions, according to a study. The Afro-Palearctic population of the painted lady butterfly, Vanessa cardui, is a single freely interbreeding, or 'panmictic' population.
Vanessa cardui is a renowned world traveler, undertaking multigenerational migrations throughout Africa, Asia, Europe, and North America. The winter breeding range of painted ladies in the Afro-Palearctic includes areas north and south of the Sahara Desert, suggesting that some painted ladies from Europe migrate across the Sahara in the autumn while others do not. Megan Reich, Daria Shipilina, and colleagues wanted to know if genomic differentiation could account for these different migratory strategies. The authors performed whole-genome sequencing and isotope geolocation on 40 painted lady butterflies collected in autumn both north and south of the Sahara Desert. Butterflies were collected in Benin, Senegal, Morocco, Spain, Portugal, and Malta. This analysis confirmed that some individuals crossed the Sahara, traveling all the way from Scandinavia, while others remained within hundreds of kilometers of their place of origin. Notably, there were no genomic differences between insects making the relatively short trip from Europe to the Mediterranean region and insects flying from Europe to West Africa. Nor could migration length be predicted by wing size, wing shape, or sex. According to the authors, the results suggest that migration distance is most likely a plastic response to environmental conditions in the species.
