The Afrotropical breeding grounds of the Palearctic-African migratory painted lady butterflies (Vanessa cardui)

Migratory insects are key players in ecosystem functioning and services, but their spatiotemporal distributions are typically poorly known. Ecological niche modeling (ENM) may be used to predict species seasonal distributions, but the resulting hypotheses should eventually be validated by field data. The painted lady butterfly (Vanessa cardui) performs multigenerational migrations between Europe and Africa and has become a model species for insect movement ecology. While the annual migration cycle of this species is well understood for Europe and northernmost Africa, it is still unknown where most individuals spend the winter. Through ENM, we previously predicted suitable breeding grounds in the subhumid regions near the tropics between November and February. In this work, we assess the suitability of these predictions through i) extensive field surveys and ii) two-year monitoring in six countries: a large-scale monitoring scheme to study butterfly migration in Africa. We document new breeding locations, year-round phenological information, and hostplant use. Field observations were nearly always predicted with high probability by the previous ENM, and monitoring demonstrated the influence of the precipitation seasonality regime on migratory phenology. Using the updated dataset, we built a refined ENM for the Palearctic-African range of V. cardui. We confirm the relevance of the Afrotropical region and document the missing natural history pieces of the longest migratory cycle described in butterflies.This work was funded by the National Geographic Society (grant WW1-300R-18); by the British Ecological Society (grant LRB16/1015); by the Research and Conservation Projects of the Fundació Barcelona Zoo; by the grant PID2020-117739GA-I00/MCIN/AEI/10.13039/501100011033 of the Spanish Ministry of Science and Innovation and the Spanish State Research Agency to G.T.; by the grant LINKA20399 from the Spanish National Research Council iLink program to G.T., C.P.B., N.E.P., and R.V.; by fellowship FPU19/01593 of the program Formación de Profesorado Universitario (FPU) to A.G.-B.; by the Turkana Basin Institute, National Geographic Society, and Whitley Fund for Nature to D.J.M.; and by grant 2018-00738 of the New Frontiers in Research Fund (Government of Canada) to G.T. and C.P.B.Significance Abstract Results Field Surveys, Larval Hostplants, and Field-Based Model Validation Monitoring Results and Population Dynamics across Regions A Refined Model for the Afrotropical Region Discussion The Afrotropical Breeding Grounds of V. cardui: Multiple Generations Shift South Toward the Tropics Diversity and Phenology of Larval Hostplants in the Afrotropics The Ecological Relevance of Delimiting Spatiotemporal Distributions in Migratory Insects Conclusion Methods December-January Field Surveys and Year-Round Monitoring Spatiotemporal Ecological Niche Modeling Data, Materials, and Software Availability Acknowledgments Supporting Information Reference