and two inverse agonists (AsIP) and agouti signalling protein agouti-related (AgRP) (Ducrest 2008, Oribe 2012). High expression of and neuropeptide et al. et al. AsIP and binding of these inverse agonists induces the production of yellow-reddish AgRP pheomelanic pigments, whereas if the agonist binds to the then more black eumelanic MC1R, pigments are produced (Ducrest 2008). Any reduction in expression of or et al. AgRP AsIP genes via DNA methylation is thus hypothesised to increase eumelanic (black) colouration. We tested this hypothesis in a model species for studies of sexual selection in the wild, the black grouse (Fig 1). The dominant colouration of black grouse is Lyrurus tetrix based (black), with the exception of small depigmented patches on the upper and underside of the wing and the conspicuous white undertail coverts (Soulsbury 2016). The feathers of et al. the neck and chest also show a blue structural colouration that exhibits high reflectance of short wavelengths in the UV-blue area (blue chroma; Siitari 2007). These sexually selected et al. traits are condition-dependent and vary substantially with age (Kervinen 2015, 2016). et al. Peak expression occurs at ages 3–5 (Kervinen 2015) and is correlated to male mating et al. success (Siitari 2007; Kervinen 2016). Furthermore, inbreeding is frequent in our et al. et al. study population, with 13% of chicks being the product of mating between close relatives ca. (Lebigre 2010), and chick mass (Soulsbury 2011) and male reproductive success et al. et al. (Höglund 2012) both show inbreeding depression. We therefore estimated the et al. contributions of age and heterozygosity towards DNA methylation and from there tested for a relationship between DNA methylation and sexual trait expression. Materials and Methods Fieldwork and colour measurement During 2002–2013 inclusive, we collected longitudinal data on male mating success and multiple sexual traits from five study sites in Central Finland (peat bogs with high visibility, ca.
and two inverse agonists agouti signalling protein (AsIP) and agouti-related neuropeptide (AgRP) (Ducrest et al. 2008, Oribe et al. 2012). High expression of AsIP and AgRP and binding of these inverse agonists induces the production of yellow-reddish pheomelanic pigments, whereas if the agonist binds to the MC1R, then more black eumelanic pigments are produced (Ducrest et al. 2008). Any reduction in expression of AgRP or AsIP genes via DNA methylation is thus hypothesised to increase eumelanic (black) colouration. We tested this hypothesis in a model species for studies of sexual selection in the wild, the black grouse Lyrurus tetrix (Fig 1). The dominant colouration of black grouse is (black), with the exception of small depigmented patches on the upper and underside of the wing and the conspicuous white undertail coverts (Soulsbury et al. 2016). The feathers of the neck and chest also show a blue structural colouration that exhibits high reflectance of short wavelengths in the UV-blue area (blue chroma; Siitari et al. 2007). These sexually selected traits are condition-dependent and vary substantially with age (Kervinen et al. 2015, 2016). Peak expression occurs at ages 3–5 (Kervinen et al. 2015) and is correlated to male mating success (Siitari et al. 2007; Kervinen et al. 2016). Furthermore, inbreeding is frequent in our study population, with ca. 13% of chicks being the product of mating between close relatives (Lebigre et al. 2010), and chick mass (Soulsbury et al. 2011) and male reproductive success (Höglund et al. 2012) both show inbreeding depression. We therefore estimated the contributions of age and heterozygosity towards DNA methylation and from there tested for a relationship between DNA methylation and sexual trait expression. Materials and Methods Fieldwork and colour measurement During 2002–2013 inclusive, we collected longitudinal data on male mating success and multiple sexual traits from five study sites in Central Finland (peat bogs with high visibility, ca. based