Evolution along a parallel/non-parallel continuum in Pacific and Atlantic feral chickens, G. gallus

Recent work indicating that feralisation is not a simple reversal of domestication has raised questions about the predictability of evolutionary change across replicated feral populations. In the present study we compare genes and traits of two independently feral populations of chickens (G. gallus) inhabiting archipelagos in Pacific and Atlantic regions to test for evolutionary parallelism and/or divergence. First, we confirm purported differences in these two populations’ ancestries are corroborated by genetic and phenotypic analyses. Indeed, whereas Pacific (Kauaii) chickens recently outcrossed with wild relatives, our genetic data from Atlantic (Bermuda) chickens is more consistent with solely domestic origins encompassing diverse G. gallus breeds. Next we used genome scans to contrast the targets of feralisation (selective sweeps) between the two independently feral populations. Two sweep loci were shared between these focal populations and this overlap is inconsistent with a null model in which selection targets are randomly distributed throughout the genome. The larger set of sweep loci from the two feral genepools were also found to govern traits that were heavily modified during G. gallus’ domestication (e.g. the nervous system and behaviour, metabolism, and reproduction). Assessment of SNPs using allelic differences and SNP annotation led to candidate SNPs for further investigation for five of the genes present. Our findings suggest that a subset of feralisation loci are shared across independently-established populations, raising the possibility that feralisation involves some degree of parallelism or convergence, though a clearer understanding of possible ‘feralisation syndromes’ will require elucidating genotype-phenotype relationships in any populations being compared.