Feralisation occurs when a domestic population is returned to the wild, escaping the cultivated settings it has been selected for, and has been considered as the reverse of domestication. The radical shifts in social, biotic and abiotic environments results in greatly increased natural and sexual selection. However, it is currently unknown if (and how) feral populations evolve in response to these altered selection regimes. Feralisation can therefore provide a unique opportunity to observe how natural and sexual selection acts on a domestic population returned to natural conditions, and especially how the genome responds to the reintroduction of such strong selective forces.
We have previously shown that Kauai Island’s feral chickens are a highly variable population with both domestic and ancient Polynesian origins. Here, we map selective sweeps in feral Kauai chickens using whole genome sequencing. 37 putative Kauai sweep regions were identified, with 26 being unique to feralisation (i.e. not present among the genomic regions that have previously been associated with domestication). To ascribe potential phenotypic functions to these genes, we utilised a laboratory-controlled equivalent to the Kauai population – an eighth generation advanced intercross between Red Junglefowl and domestic layer birds that has been used previously for both QTL and expression QTL studies of male ornaments and female reproductive traits (comb mass and fecundity). Certain sweep genes exhibited significant correlations with comb mass, maternal brooding behaviour and fecundity.
Together, our analyses of feral and intercrossed genomes indicate that adaptations to feral and domestic environments involve different genome regions and feral chickens show some evidence of adaptation at genes associated with sexual selection and reproduction. At the genomic level, feralisation is not simply a reversal of the domestication process. A comprehensive understanding of feralisation will thus bring unique evolutionary insights, while facilitating ‘evolutionarily-enlightened’ management practices for animals and crops.