Figure S1 Genetic structure within individual drainages. Unless otherwise indicated, Structure analyses were based on neutral microsatellite loci using the default settings outlined in the manuscript. All location names correspond to Fig.  1 and Table  S1. The best supported number of groups (K) was inferred from plots of the likelihood distribution or, if no clear mode was detected, based on ΔK proposed by Evanno et  al. (2005).

Table S1 Sampling locations in three major European drainages.

Table S2 Microsatellite markers used in this study.

Table S3 Pairwise FST values calculated based on ten neutral loci.

Table S4 Difference between the observed Hardy–Weinberg heterozygosity (He) and the expectation at mutation-drift equilibrium (Heq) under a stepwise mutation model.

Table S5 Frequency of Atlantic-like (AT), marble trout-like (MA) and Mediterra-nean-like (ME) alleles (see footnote) at the two diagnostic microsatellite markers JMS1M1 and JMS2M1 for all populations.

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