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Dryad

Male and female adult zebra finch (Taeniopygia guttata) gonad RNAseq associated with: Relaxed purifying selection maintains a sex-linked supergene polymorphism in zebra finches

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Mar 08, 2024 version files 100.23 GB

Abstract

Recent years have seen an explosion in examples of inversion polymorphisms, where recombination is suppressed between haplotypes, acting as supergenes to control complex traits. However, an enduring problem in evolutionary biology is understanding how these inversion polymorphisms are maintained, often for long periods of time. Here, we test alternate theories for how balancing selection maintains supergenes and explore the molecular evolution and expression of a large, sex-linked inversion polymorphism in a passerine bird, the zebra finch (Taeniopygia guttata) responsible for most of the genetic variation in sperm morphology. We find evidence for degeneration within the supergene characterised by relaxed purifying selection and an excess of nonsynonymous differences which, combined with signatures of balancing selection, is indicative of associative overdominance protecting heterozygotes from deleterious recessive alleles. Furthermore, we find that the transcriptome acts to mitigate the negative consequences of relaxed purifying selection through the more equal expression of those most highly diverged, and potentially degenerated, alleles.