Journal
MOLECULAR BIOLOGY AND EVOLUTION
Volume 38, Issue 12, Pages 5275-5291Publisher
OXFORD UNIV PRESS
DOI: 10.1093/molbev/msab277
Keywords
sex chromosome; neo-sex chromosome; recombination; degeneration; vertebrate; bird
Funding
- Swedish Research Council
- Knut and Alice Wallenberg Foundation
- Kvismare Bird Observatory [198]
- NBIS/SciLifeLab
- Knut and Alice Wallenbergs Stiftelse as part of the National Bioinformatics Infrastructure Sweden (NBIS) at SciLifeLab
- Kungliga Fysiografiska Sallskapet i Lund
- Erik Philip-Sorensen's Foundation
- Stiftelsen Olle Engkvist Byggmastare
- Wenner-Gren Stiftelserna
- European Research Council under the European Union [679799, 742646]
- Vetenskapsradet [2016-00689, 2015-05149, 2016-04391]
- Council for Research infrastructure, RFI
- European Research Council (ERC) [679799, 742646] Funding Source: European Research Council (ERC)
- Swedish Research Council [2015-05149, 2016-04391, 2016-00689] Funding Source: Swedish Research Council
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The study reveals the evolutionary history of avian sex chromosomes, including translocation of an added region to Z and W, long-term recombination suppression, and degeneration of the added-W, indicating the complexity and diversity of avian sex chromosome evolution.
How the avian sex chromosomes first evolved from autosomes remains elusive as 100 million years (My) of divergence and degeneration obscure their evolutionary history. The Sylvioidea group of songbirds is interesting for understanding avian sex chromosome evolution because a chromosome fusion event similar to 24 Ma formed neo-sex chromosomes consisting of an added (new) and an ancestral (old) part. Here, we report the complete female genome (ZW) of one Sylvioidea species, the great reed warbler (Acrocephalus arundinaceus). Our long-read assembly shows that the added region has been translocated to both Z and W, and whereas the added-Z has retained its gene order the added-W part has been heavily rearranged. Phylogenetic analyses show that recombination between the homologous added-Z and -W regions continued after the fusion event, and that recombination suppression across this region took several million years to be completed. Moreover, recombination suppression was initiated across multiple positions over the added-Z, which is not consistent with a simple linear progression starting from the fusion point. As expected following recombination suppression, the added-W show signs of degeneration including repeat accumulation and gene loss. Finally, we present evidence for nonrandom maintenance of slowly evolving and dosage-sensitive genes on both ancestral- and added-W, a process causing correlated evolution among orthologous genes across broad taxonomic groups, regardless of sex linkage.
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