Abstract
The Hyalomma marginatum tick is endemic in several Mediterranean countries, from the Maghreb to the Iberian Peninsula and the eastern Mediterranean basin. Its range is gradually expanding towards northern Europe. Described since the 1950s in Corsica, this tick was reported in mainland France in 2016. It therefore seems that we are witnessing a biological invasion of this species in France. Such change in species distribution can be due to three main eco-evolutionary drivers: migration change, phenotypic change and environmental change. First, we studied the migration pattern of this ticks and the origin of this invasion as revealed by its current genetic structuring. A campaign to collect samples in France between 2016 and 2023 and collaborations with foreign partners provided us with more than 600 individuals of H. marginatum. Our phylogeography study using mitochondrial markers enabled us to define three differentiated genetic clusters in mainland France, indicating potentially different origins and therefore several discrete colonization events by this tick. These results will be confirmed using nuclear markers developed by sequence capture targeting ultraconserved elements designed in Arachnida. Second, phenotypic changes allowing successful establishment in the novel environment can be due to either to phenotypic plasticity or to evolutionary changes. These two hypotheses were tested with two different experiments: one with field ticks brought back to the laboratory, where life-history traits were compared between different French populations to see if there had been any local adaptation; the other with laboratory-bred ticks, which were placed into the field to see whether or not their life cycle was successful and how long this cycle lasted as a function of environmental conditions. The latter showed that H. marginatum can complete its cycle in a climate that differs other than that of the Mediterranean, and that the species is likely to extend its range still further.