Results of Mantel tests conducted to test for isolation by distance (geographical distance vs. FST/(1-FST)) in the program IBDWS for the cryptic Gammarus fossarum species type A and B in different drainages.

1“group” indicates the species and drainage included in the analysis. Two main clusters of type B were observed in the Rhine (see Fig. 2). Isolation by distance was assessed only within the larger cluster, B1.2***P3The regression slopes (IBD slope) and their confidence intervals (95% CI) are indicated if significantly different from zero. The slopes were significantly higher in type A (Rhine) than type B (Rhone) irrespective of the distance measure used.