A non-coding region near Follistatin controls head colour polymorphism in the Gouldian finch

Abstract

Discrete colour morphs coexisting within a single population are common in nature. In a broad range of organisms, sympatric colour morphs often display major differences in other traits, including morphology, physiology or behaviour. Despite the repeated occurrence of this phenomenon, our understanding of the genetics that underlie multi-trait differences and the factors that promote the long-term maintenance of phenotypic variability within a freely interbreeding population are incomplete. Here, we investigated the genetic basis of red and black head colour in the Gouldian finch ( Erythrura gouldiae ), a classic polymorphic system in which naturally occurring colour morphs also display differences in aggressivity and reproductive success. We show that the candidate locus is a small (approx. 70 kb) non-coding region mapping to the Z chromosome near the Follistatin ( FST ) gene. Unlike recent findings in other systems where phenotypic morphs are explained by large inversions containing hundreds of genes (so-called supergenes), we did not identify any structural rearrangements between the two haplotypes using linked-read sequencing technology. Nucleotide divergence between the red and black alleles was high when compared to the remainder of the Z chromosome, consistent with their maintenance as balanced polymorphisms over several million years. Our results illustrate how pleiotropic phenotypes can arise from simple genetic variation, probably regulatory in nature.

Carotenoid pigmentation in salmon: variation in expression at BCO2-l locus controls a key fitness trait affecting red coloration

“…Consistent with our findings, studies in reptiles and birds have found that colour polymorphisms can often be explained by a single major effect locus [38,43]. The role of a single gene in driving differences between colour morphs is surprising given that morphs often show correlated differences in other key traits [38,43]. Indeed, differences in reproduction, predation, and physiology have been associated with carotenoid pigmentation in salmonids [16][17][18][19][44][45][46][47].…”

Genome Report:De novogenome assembly and annotation for the Taita white-eye (Zosterops silvanus)

“…Linked-read sequencing has a huge potential for generating decent draft bird genome assemblies (Toomey et al 2018, Boman et al 2019, Kinsella et al 2019, Lutgen et al 2020. 10X Genomics Chromium is the most commonly used linked-read library preparation at present, but other linked-read methods , Redin et al 2019 are equally promising but have yet to be tested on birds.…”

Genetics and evidence for balancing selection of a sex-linked colour polymorphism in a songbird

“…First, both independent approaches highlight the same genomic region upstream of the follistatin gene, providing strong evidence of its functional role in generating the colour polymorphism. Second, unlike Toomey et al 52 , our analysis incorporates data from wild birds, making clear the relevance of this region to nondomesticated populations. Finally, our simulations and evolutionary reconstructions add key historical context to how and why this polymorphism has evolved and is maintained in the wild.…”