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Each year, painted lady butterflies (Vanessa cardui) travel thousands of kilometers between Africa and Europe in search of suitable breeding conditions. A new study, involving researchers from the Institute of Science and Technology Austria (ISTA), suggests that the butterflies’ varying migration distances are influenced by environmental factors rather than genetic differences. The findings, published in PNAS Nexus, provide insights into the mechanisms shaping insect migration.
Painted lady butterflies follow a multi-generational migration cycle. The journey begins in Northwest Africa, with individuals flying across the Mediterranean into Europe. Later generations continue the migration northward, reaching as far as Sweden before returning south in autumn. Some butterflies complete the full journey to sub-Saharan Africa, while others remain in the Mediterranean.
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To investigate the factors influencing these migratory routes, researchers collected butterflies from multiple locations, including Benin, Senegal, Morocco, Spain, Portugal and Malta. Using isotope analysis, they traced the geographic origins of individual butterflies, revealing a diverse range of migratory behaviors.
The researchers applied isotope geolocation, a method that links an organism’s isotopic composition to the environment where it developed. Since a butterfly’s wings retain the isotopic signature of the plants it consumed as a caterpillar, this technique allowed scientists to estimate its place of origin.
Some butterflies migrated long distances across the Sahara, while others stayed in Mediterranean regions. Despite these differences in travel behavior, genome sequencing revealed no genetic variations distinguishing short- and long-distance migrants.
Unlike some bird species, where specific genetic variants influence migration routes, painted lady butterflies appear to rely on environmental cues. Researchers suggest that phenotypic plasticity – the ability of an organism to change behavior in response to external conditions – plays a key role.
For example, butterflies in Sweden may receive strong migratory cues due to rapidly shortening days at the end of summer, prompting them to travel farther south. In contrast, butterflies in southern Europe may not experience the same environmental triggers, leading them to migrate shorter distances.
The migration of painted lady butterflies remains less understood than that of other species, such as monarch butterflies. Future research will examine whether these findings apply to broader populations of painted ladies or to other insect species with complex migratory patterns.
Reference: Reich MS, Shipilina D, Talla V, et al. Isotope geolocation and population genomics in Vanessa cardui: Short- and long-distance migrants are genetically undifferentiated. PNAS Nexus. 2025;4(2):pgae586. doi: 10.1093/pnasnexus/pgae586
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