However, we observed a colour phenotype x environment interaction, whereby α-diversity decreased with increases in MC1R mutation number (agouti: 0, intermediate: 1, black: 2) at rural sites (β = − 29.39 ± 12.26 SE, t = − 2.40, p = 0.02) but increased with melanism mutation number at city sites (β = 37.27 ± 13.86 SE, t = 2.69, p < 0.01; Fig. 2). This evidence concerns the gene MC1R and freckles.