Fig. 3

S. solidus growth differs significantly between host populations and between geographically clustered parasite strains. Naïve laboratory bred F1 offspring from sticklebacks from lake Großer Plöner See, Germany (DE), and Lake Skogseidvatnet, Norway (NO), were experimentally infected with single S. solidus larvae from nine different locations (‘strains’) across the Northern Hemisphere. Fish were dissected 55 (+/− 2) days after exposure to the parasite. The parasite index (PI) was calculated as the proportion of the parasite’s weight from the total weight of infected fish. (a) DE and NO hosts were infected with four different European S. solidus strains (contrast 1). Black and white dots represent individuals; violet: mean parasite indices in DE hosts; orange: mean parasite indices in NO hosts (Additional file 1: Table S6). (b) Parasite indices in DE hosts (contrast 2). Black dots and bars indicate the mean and the standard deviation. Color coding follows Fig. 2. (c) Parasite indices in NO hosts (contrast 3). Black dots and bars indicate the mean and the standard deviation. Color coding follows Fig. 2