Figure 1. Map of France with administrative division to regions (dark-bordered areas) and departments within them (light-bordered areas), showing the distribution of the invasive signal crayfish Pacifastacus leniusculus (small empty circles; based on [4], [19], [21], [44]) and approximate location of analysed populations (triangles), and the recent status of the native white-clawed crayfish Austropotamobius pallipes (green shading) and reported cases of its mass mortalities (red crosses and black dots).

Distribution of A. pallipes is based on a 2006 survey [23] (white: no known population in a department, pale green: 1–5, medium: 6–25, dark: 25–150 populations). Red crosses with years indicate mass mortalities most likely caused by crayfish plague reported since the 1990s ([10], [12], [13], [14], [15], [45], [46]; T. Duperray and T. Pantarotto, pers. comm.); additional mortalities ascribed to crayfish plague were reported between 2001 and 2005 from departments marked by black dots (according to [23]). Bold crosses mark outbreaks in which A. astaci has been confirmed by molecular detection and genotyped (see Discussion). The prevalence of Aphanomyces astaci in sampled signal crayfish populations is expressed by colour: no reliable detection of the pathogen (white triangles), low prevalence (1–30%, yellow), medium prevalence (31–60%, orange) and high prevalence (61–100%, red triangles); the number of analysed individuals in the respective population is indicated by symbol size (small triangle: <10 individuals, large triangle: 10+ individuals). Regions discussed in the text are abbreviated: Al – Alsace, Au – Auvergne, Ba-No – Basse-Normandie, Ce – Centre, Ch-Ar – Champagne-Ardenne, La-Ro – Languedoc-Rousillon, Li – Limousin, Lo – Lorraine, Po-Ch – Poitou-Charentes, Rh-Al – Rhône-Alpes; Lake Geneva (Lac Léman) is marked by L within the triangle. The distance scale depends on latitude (top: 51.5°N, bottom: 41°N) and reflects the map projection.