Conclusions and future research on the evolution and maintenance of melanin-based colour polymorphism
In this study we demonstrate that the melanin-associated phenotypic variation in the tawny owl appear to be regulated by non-exonic polymorphisms in genes not traditionally associated with colour genes, as has been reported also for the barn owl (Luis M. San-Jose et al., 2017). This is not necessarily surprising, because quantitative differences in feather colour in the chicken have also been found to be regulated by such non-traditional genes (Fogelholm et al., 2020). While our results might be interpreted as a step forward to understand the evolution and maintenance of intra-specific colour polymorphism, it will require substantial follow-up work to obtain stronger lines of evidence. For example, screening the tawny owl genome with densities higher than those provided by RADseq while information using transcriptomic and epigenetic data is among the most robust future research lines to fully pin down the long theorized (genetic) linkage between colour producing genes and melanin-associated phenotypes (Fig. 3).