Evolution along a parallel/non-parallel continuum in Pacific and
Atlantic feral chickens, G. gallus
Abstract
Recent work indicates that feralisation is not a simple reversal of
domestication, and therefore raises questions about the predictability
of evolution across replicated feral populations. In the present study
we compare genes and traits of two independently established feral
populations of chickens (G. gallus) that inhabit archipelagos within the
Pacific and Atlantic regions to test for evolutionary parallelism and/or
divergence. We find that these two feral populations share close genetic
similarities despite the lack of any current gene flow between them.
Next, we used genome scans to contrast the targets of feralisation
(selective sweeps) between the two independently feral populations from
Bermuda and Hawaii. Three sweep loci (each identified by multiple
detection methods) were shared between feral populations, and this
overlap is inconsistent with a null model in which selection targets are
randomly distributed throughout the genome. In the case of the Bermudian
population, many of the genes present within the selective sweeps were
either not annotated or of unknown function. Of the nine genes that were
identifiable, five were related to behaviour, with the remaining genes
involved in bone metabolism, eye development, and the immune system. Our
findings suggest that a subset of feralisation loci (i.e. genomic
targets of recent selection in feral populations) are shared across
independently-established populations, raising the possibility that
feralisation involves some degree of parallelism or convergence. A
clearer understanding of whether these reflect selection for similar
functional traits (‘feralisation syndromes’) will require elucidating
genotype-phenotype relationships in any populations being compared.