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.