Limits to Hyalomma marginatum range expansion in France: lessons from population transplant

Hyalomma marginatum occurs across a wide range of environments, from Mediterranean lowlands in North Africa to continental steppes in Eastern Europe and has recently colonized diverse habitats in southern France. This ecological breadth raises key questions regarding its capacity to complete its life cycle under contrasting environmental conditions and whether its current distribution in France reflects ecological limits. In this study, we investigated the thermal tolerance and developmental performance of H. marginatum through a population transplant experiment. Engorged females and nymphs reared under controlled conditions were released at two climatically distinct sites: Pompignan (Gard), where the species is highly abundant and characterized by a Mediterranean climate, and Gardouch (Haute-Garonne), where the species is not yet established and experiences a southwestern basin climate. At each site, individuals were placed in two contrasting microhabitats (open versus forested environments) to assess the influence of local and microclimatic conditions on life cycle timing and survival. Our results show that H. marginatum is able to complete its entire life cycle at both sites with broadly similar phenology. In contrast, microhabitat had a stronger influence on development and survival, indicating substantial phenotypic plasticity in response to local environmental conditions. The absence of established populations in Gardouch area therefore cannot be readily explained by climatic constraints alone, and may instead reflect dispersal limitations, unsuitable timing of introductions, or other environmental factors such as humidity or vegetation structure. Our findings suggest that H. marginatum has the potential to further expand its range in France in the coming years.