Fig. 4

Geographical cline analysis for Bufo spinosus (left, with Q_s-values close to unity at vertical axis) and B. bufo (right, with Q_s-values close to zero at vertical axis) in a transect in northwestern France. Study populations are as in Table 1 and small solid dots are population averages. Clines were fitted to a) Structure Q-scores (with blue shading) and NewHybrids posterior probabilities for the species (grey shadings with the transition towards B. spinosus left and towards B. bufo right). Note that the graph to the right shows the central part of the transect in detail. Furthermore, b) the loading on the first PCA axis, based on the panel of 12 microsatellites, c) the B. spinosus frequency of the mtDNA marker, d, e) morphological identification probabilities (details see text) and f–i) the B. spinosus frequency of four SNP markers. The 95% credible cline regions are highlighted by grey shadings. The vertical blue line gives the position of population 10, at Beaulieu. Locality altitudes are plotted in red