Round-trip across the Sahara: Afrotropical Painted Lady butterflies recolonize the Mediterranean in early spring

Abstract

The Palearctic-African migratory circuit has been typically associated with birds. Very few insects are known to endure annual trans-Saharan circuits, but the Painted Lady butterfly () is an exception. While it was demonstrated that this species massively migrates from Europe to the Afrotropics during the autumn, the existence of a reverse migration from the Afrotropics to Europe in the early spring remains hypothetical. Here, we analysed wing stable hydrogen isotope values (δH) of migrants collected from February to April across the circum-Mediterranean region. We assessed their region of natal origin by comparing their wing isotope signature predicted δH values (isoscape). The results unambiguously demonstrate a sub-Saharan origin for many individuals, especially those collected in February, representing the first tangible evidence for a reverse northwards trans-Saharan migration in spring. This work supports the view that the Afrotropics (mostly exploited from September to February) is key in the Palearctic-African population dynamics. This species relies on both temperate and tropical habitats to complete their multigenerational cycle, an unprecedented adaptation for butterflies and for most migratory insects. Such a migratory circuit has strong parallelisms with those of migratory birds.

Spatio-temporal ecological niche modelling of multigenerational insect migrations

“…The model also predicts suitable breeding habitat during the winter months in certain areas of Northern Africa, and in a minor proportion in the circum-Mediterranean coastal areas. Some populations are suspected to spend the entire winter months in these areas [10,27,30]. However, predicted suitable breeding habitat is higher in the Afrotropics than in the Mediterranean region between December and February, supporting the view that the population core of the species breeds in winter in the sub-Sahara in higher numbers than known sites in North Africa or Mediterranean Europe.…”

Timing of mating, reproductive status and resource availability in relation to migration in the painted lady butterfly,Vanessa cardui

“…In accordance with the oogenesis-flight syndrome, the first prediction -that the mating frequency will be lower in the emergence areas that represent the source of migrants than in the destination areas where breeding occurs -was confirmed from samples in Morocco in spring and autumn. The key role of this region as the source of migrants colonizing Spain in the spring is fully supported by field work that has led to the discovery of mass emergence sites throughout the region, by multiple observations of northward migration, and by isotope and pollen markers of butterflies collected in Spain (Stefanescu et al, 2012;Talavera et al, 2018;Suchan et al, 2019). Likewise, the importance of the region as a breeding area in autumn has been confirmed by extensive field work in the last decade coupled with isotope markers (Stefanescu et al, 2016(Stefanescu et al, , 2017.…”

“…To assess their reproductive status and its relationship with migration, wild females were collected in Morocco (Maghreb, NW Africa) and in Catalonia and the Balearic Islands (NE Spain). The Maghreb is the main source of the migrant painted ladies that colonise Spain in spring, and an important destination area in autumn for breeding butterflies of European and sub-Saharan origin (Stefanescu et al, 2011(Stefanescu et al, , 2016(Stefanescu et al, , 2017Talavera et al, 2018;Suchan et al, 2019). Painted ladies remain in this region in low numbers throughout the winter until the spring generation emerges and emigrates to Europe.…”

Strong impacts of smoke polluted air demonstrated on the flight behaviour of the painted lady butterfly (Vanessa cardui L.)

“…V. cardui generally maintains a large population through multi successive generations every year (Stefanescu et al ., 2013; Talavera & Vila, 2017). V. cardui have excellent flight capacities, reflected in their annual mass migration between Africa and Europe (Talavera et al ., 2018; Menchetti et al ., 2019; Suchan et al ., 2019). Normally, they migrate from Europe to the Afrotropics in autumn and also evidence proved that they had a reverse northwards trans‐Saharan migration in Spring (Talavera & Vila, 2017; Talavera et al ., 2018).…”