Unique structure and positive selection promote the rapid divergence of Drosophila Y chromosomes
- University of Rochester, United States
- Cornell University, United States
- University of Nebraska-Lincoln, United States
Abstract
Y chromosomes across diverse species convergently evolve a gene-poor, heterochromatic organization enriched for duplicated genes, LTR retrotransposons, and satellite DNA. Sexual antagonism and a loss of recombination play major roles in the degeneration of young Y chromosomes. However, the processes shaping the evolution of mature, already degenerated Y chromosomes are less well-understood. Because Y chromosomes evolve rapidly, comparisons between closely related species are particularly useful. We generated de novo long read assemblies complemented with cytological validation to reveal Y chromosome organization in three closely related species of the Drosophila simulans complex, which diverged only 250,000 years ago and share >98% sequence identity. We find these Y chromosomes are divergent in their organization and repetitive DNA composition and discover new Y-linked gene families whose evolution is driven by both positive selection and gene conversion. These Y chromosomes are also enriched for large deletions, suggesting that the repair of double-strand breaks on Y chromosomes may be biased toward microhomology-mediated end joining over canonical non-homologous end-joining. We propose that this repair mechanism contributes to the convergent evolution of Y chromosome organization across organisms.
Data availability
Genomic DNA sequence reads are in NCBI's SRA under BioProject PRJNA748438.All scripts and pipelines are available in GitHub(https://github.com/LarracuenteLab/simclade_Y) and the Dryad digital repository (doi:10.5061/dryad.280gb5mr6).
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Genome sequencing of males in Drosophila simulans cladeNCBI Bioproject, PRJNA748438.
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Unique structure and positive selection promote the rapid divergence of Drosophila Y chromosomesDryad Digital Repository, doi:10.5061/dryad.280gb5mr6.
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Drosophila mauritiana Genome sequencingNCBI Bioproject, PRJNA158675.
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DSPR Founder GenomesNCBI Bioproject, PRJNA418342.
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Drosophila simulans Raw sequence readsNCBI Bioproject, PRJNA477366.
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Novel quality metrics identify high-quality assemblies of piRNA clustersNCBI Bioproject, PRJNA618654.
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Nanopore-based assembly of many drosophilid genomesNCBI Bioproject, PRJNA675888.
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Transcriptome sequencing of Drosophila simulans cladeNCBI Bioproject, PRJNA541548.
Article and author information
Author details
Colin D Meiklejohn
Funding
National Institute of General Medical Sciences (R35GM119515)
- Amanda M Larracuente
National Institute of General Medical Sciences (R01GM123194)
- Colin D Meiklejohn
National Science Foundation (MCB 1844693)
- Amanda M Larracuente
Damon Runyon Cancer Research Foundation (DRG: 2438-21)
- Ching-Ho Chang
College of Arts and Sciences, University of Nebraska-Lincoln
- Colin D Meiklejohn
University of Rochester
- Amanda M Larracuente
University of Rochester
- Ching-Ho Chang
Ministry of Education, Taiwan
- Ching-Ho Chang
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2022, Chang et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Unique structure and positive selection promote the rapid divergence of Drosophila Y chromosomes
eLife 11:e75795.
https://doi.org/10.7554/eLife.75795
Further reading
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Gene duplication drives evolution by providing raw material for proteins with novel functions. An influential hypothesis by Ohno (1970) posits that gene duplication helps genes tolerate new mutations and thus facilitates the evolution of new phenotypes. Competing hypotheses argue that deleterious mutations will usually inactivate gene duplicates too rapidly for Ohno’s hypothesis to work. We experimentally tested Ohno’s hypothesis by evolving one or exactly two copies of a gene encoding a fluorescent protein in Escherichia coli through several rounds of mutation and selection. We analyzed the genotypic and phenotypic evolutionary dynamics of the evolving populations through high-throughput DNA sequencing, biochemical assays, and engineering of selected variants. In support of Ohno’s hypothesis, populations carrying two gene copies displayed higher mutational robustness than those carrying a single gene copy. Consequently, the double-copy populations experienced relaxed purifying selection, evolved higher phenotypic and genetic diversity, carried more mutations and accumulated combinations of key beneficial mutations earlier. However, their phenotypic evolution was not accelerated, possibly because one gene copy rapidly became inactivated by deleterious mutations. Our work provides an experimental platform to test models of evolution by gene duplication, and it supports alternatives to Ohno’s hypothesis that point to the importance of gene dosage.
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