Supplementary information for: Redundancy analysis, genome-wide association studies, and the pigmentation of brown trout (Salmo trutta L.)

The association of molecular variants to phenotypic variation is a main issue in biology, often tackled with genome-wide association studies (GWAS). GWAS are challenging, with increasing, but still limited use in evolutionary biology. We used redundancy analysis (RDA) as a complimentary ordination approach to single- and multi-trait GWAS to explore the molecular basis of pigmentation variation in brown trout (Salmo trutta) belonging to wild populations impacted by hatchery fish. Based on 75,684 single nucleotide polymorphic (SNP) markers, RDA, single- and multi-trait GWAS allowed us to extract 337 independent "colour patterning loci" (CPLs) associated with trout pigmentation traits, such as the number of red and black spots on flanks. Collectively, these CPLs (i) mapped onto 35 out of 40 brown trout linkage groups indicating a polygenic genomic architecture of pigmentation, (ii) were found associated with 218 candidate genes, including 197 genes formerly mentioned in the literature dealing with skin pigmentation, skin patterning, differentiation or structure notably in a close relative, the rainbow trout (Onchorhynchus mykiss), and (iii) related to functions relevant to pigmentation variation (e.g., calcium- and ion-binding, cell adhesion). Annotated CPLs include genes with well-known pigmentation effects (e.g., PMEL, SLC45A2, SOX10), but also markers associated with genes formerly found expressed in rainbow or brown trout skins. RDA was also shown useful to investigate management issues, especially the dynamics of trout pigmentation submitted to several generations of hatchery introgression.