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. 2019 Mar;32(3):194-204.
doi: 10.1111/jeb.13410. Epub 2019 Jan 11.

Sexually Dimorphic Gene Expression and Transcriptome Evolution Provide Mixed Evidence for a fast-Z Effect in Heliconius

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Free PMC article

Sexually Dimorphic Gene Expression and Transcriptome Evolution Provide Mixed Evidence for a fast-Z Effect in Heliconius

Ana Pinharanda et al. J Evol Biol. .
Free PMC article

Abstract

Sex chromosomes have different evolutionary properties compared to autosomes due to their hemizygous nature. In particular, recessive mutations are more readily exposed to selection, which can lead to faster rates of molecular evolution. Here, we report patterns of gene expression and molecular evolution for a group of butterflies. First, we improve the completeness of the Heliconius melpomene reference annotation, a neotropical butterfly with a ZW sex determination system. Then, we analyse RNA from male and female whole abdomens and sequence female ovary and gut tissue to identify sex- and tissue-specific gene expression profiles in H. melpomene. Using these expression profiles, we compare (a) sequence divergence and polymorphism; (b) the strength of positive and negative selection; and (c) rates of adaptive evolution, for Z and autosomal genes between two species of Heliconius butterflies, H. melpomene and H. erato. We show that the rate of adaptive substitutions is higher for Z than autosomal genes, but contrary to expectation, it is also higher for male-biased than female-biased genes. Additionally, we find no significant increase in the rate of adaptive evolution or purifying selection on genes expressed in ovary tissue, a heterogametic-specific tissue. Our results contribute to a growing body of literature from other ZW systems that also provide mixed evidence for a fast-Z effect where hemizygosity influences the rate of adaptive substitutions.

Keywords: gene expression; genomics; insects; molecular evolution; sex chromosomes.

Figures

Figure 1
Figure 1
Expression level of Z and autosomal genes. Median expression level of Z genes is significantly lower than autosomal genes (< 0.05). Notches on boxplot display the confidence intervals around the median

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