Genome sharing in gonochorous species is expected to result in intraspecific conflicts due to intersexual competition. The emergence of sexual dimorphism is thus connected to the evolution of mechanisms that, starting from a similar genomic background, produce sufficiently disparate phenotypes to attenuate sexually antagonistic selection. From a molecular perspective it can be briefly summarised by sex-specific differences in gene expression, splicing, non-coding regulation or epigenetic marks. The tawny owl (Strix aluco) is a reverse sexually dimorphic species where females and males evolved distinct body sizes (smaller males), which results in sex-specific roles and therefore are a robust example of resolved sexual conflict. Here we explore, transcriptional variation among 27 juvenile tawny owls with the objective of investigating molecular signatures of resolved sexual conflict. Tawny owls also exhibit melanin-based colour polymorphism, which, given the body size differences between sexes, suggest a sex-specific onset of pigmentation. Our results show substantial sex-specific variation in terms of differentially expressed genes, single nucleotide polymorphisms and alternative exon usage in genes involved in life history traits (ZGRF1, VLDLR), behaviour (GSK3B, SLC12A) and aspects of growth (GHR, EGF, EPS8L2). Exploring sex-specific DEG revealed enrichment for biological functions associated with melanogenesis and pigment granulation in males, which together with the identification of a single up-regulated gene involved in melanogenesis (RAB38) in brown males strongly suggests different timings for the onset of pigmentation between sexes. Overall, our results reveal some of the sex-specific molecular signatures expected to be observed in the context of a resolved sexual conflict.

Feathers comprise a series of evolutionary innovations but also harbor colour, a key biological trait known to co-vary with life history or complex traits. Those relationships are particularly true in melanin-based pigmentation species due to known pleiotropic effects of the melanocortin pathway – originating from melanin-associated phenotypes. Here we explore the molecular basis of melanin coloration and expected co-variation at the molecular level in the melanin-based, colour polymorphic system of the tawny owl (Strix aluco). An extensive body of literature has revealed that grey and brown tawny owl colour morphs differ in a series of life history and behavioral traits. Thus, it is plausible to expect co-variation also at molecular level between colour morphs. To investigate this possibility, we assembled the first draft genome of the species against which we mapped ddRADseq reads from 220 grey and 150 brown morphs - representing 10 years of pedigree data from a population in Southern Finland - and explored genome-wide associations with colour phenotype. Our results revealed putative molecular signatures of cold adaptation strongly associated with the grey phenotype, namely a non-synonymous substitution in MCHR1, plus 2 substitutions in non-coding regions of FTCD and FAM135A whose genotype combinations obtained a predictive power of up to 100% (predicting grey colour). These suggest molecular basis of cold environment adaptations predicted to be grey-morph specific. Our results potentially reveal part of the molecular machinery of melanin-associated phenotypes and provide novel insights towards understanding the functional genomics of colour polymorphism in melanin-based pigmented species.

Feathers comprise a series of evolutionary innovations but also harbor colour, a biological trait with immense selective value and known to co-vary with life history or complex traits. Such an intricate web of relationships is particularly true in melanin-based pigmentation species, mainly due to known pleiotropic effects of the melanocortin pathway – originating so-called melanin-phenotypes. Here we explored the molecular basis of melanin coloration and expected co-variation at molecular level in a melanin-based, colour polymorphic benchmark system, the tawny owl. An extensive body of literature has revealed grey and brown tawny owl color morphs differ in a series of life history and behavioral traits. We assembled the first draft genome of the species against which we mapped ddRADseq reads from 220 grey and 150 brown morphs - representing 10 years of pedigree data from a population in Southern Finland - and explored genome-wide associations with colour phenotype. Our results revealed molecular signatures of cold adaptation strongly associated with grey coloration, namely a non-synonymous substitution in MCHR1 detected when comparing genomes, plus 2 substitutions in non-coding regions of FTCD and FAM135A whose genotype combinations obtained a predictive power of up to 100% (predicting grey colour). All these genes have functions related to energy homeostasis, fat deposition and control of starvation response and indicate the molecular basis of some cold environment adaptations predicted to be grey-morph specific. our results unveil part of the molecular machinery of melanin-phenotypes and shed light on the maintenance and evolution of colour polymorphism in melanin-based pigmented species.