Candidate genes
From a total of 132,343 SNPs, 115 showed absolute loading scores on the RDA1 and RDA2 distributions deviating from the mean by more than six times the standard deviation. Out of these 115 loci, the 2000-bp flanking region of 23 of them (20%) mapped against a total of 15 annotated genes. Potentially relevant reported functions of the identified genes in vertebrates included the following: heart and muscle development (DPF3; Lange et al. 2008); heavy metal sensitiveness and detoxification (ABCB6; Rakvács et al. 2019); high-pitched hearing (KCNQ4; Liu et al. 2011); laying performance and egg quality (IOV7; Huang et al. 2019; Wu et al. 2018); DNA crosslink repair and tolerance to UV light and camptothecin-induced DNA damage (FANCM; Rosado et al. 2009); megakaryocytopoiesis, platelet formation (TPOR; Ocampo Daza & Larhammar 2018); trait regulation of energy balance through effects on feeding behavior and adaptive thermogenesis (KSR2; Guo et al. 2017); and modulation of fasting blood glucose (G6PC2; Matschinsky 2005; O’Brien 2013), possibly in response to stress (Boortz et al. 2016). PairwiseF ST values based on SNP loci linked to functional candidate genes revealed relative patterns of differentiation similar to those based on neutral markers, but yielded considerably higher absolute values. UCSD showed the highest pairwise F STscores with isolated forms townsendi (0.54) and pontilis(0.28), an average of 0.32 with northern forms, and the lowest value with pinosus (0.21) (Table 2). Per-locusF ST values between UCSD and the sister grouppinosus showed moderate to high levels of divergence (0.26 to 0.51) in genes TPOR, ABCB6, FANCM, KCNQ4 and IOV7, with the rest of the genes ranging from 0 to 0.2 F ST values (Table S2, Supporting Information).