Broader implications for feralisation
As well as the genetic similarities that we observe between our two feral chicken populations, with a significant number of overlapping selective sweep regions, we also see a return to the ‘wild’ phenotype in both cases. Other examples of such reversion in coat colour in feral populations also come from feral boar populations in the US and dingo populations in Australia. In the case of the feral boar, one longitudinal study found that domestic coat colour individuals showed a mark decrease over a 13 year period, with a commensurate increase in the black (wild type) coloration over the same period (Gipson, Lee et al. 2006), with another study finding the same black coloration to be the dominant adult phenotype in Texan populations (Mapston 2007). However, another longitudinal study found the reverse, with an increase in spotted individuals at the expense of black individuals (Mayer, Brisbin Jr et al. 1989), though they ascribe this to human hunting preferences. Similarly, dingo populations show an excess of classical ginger coat colour phenotypes over white domestic ones, even when a high degree of domestic introgression/ hybridisation is present (Tatler, Prowse et al. 2021) (Newsome and Corbett 1985).
Thus, it appears that feralisation still has strong selection against more novelty traits produced through domestication, but that domestication also has many advantageous polymorphisms for feral populations, but that these are at low/ intermediate frequencies in normal domesticated populations. The importance of domestication-related alleles controlling other, less visible phenotypes during feralisation is also shown by the location of a sweep at a well-known domestication-related gene (SEMA3A ) that participates in nervous system development, and the fact that chromopainter indicates that many of the alleles in feralisation-related sweeps appear to be domestic in origin.