RT Journal Article
SR Electronic
T1 Genomics of an avian neo-sex chromosome reveals the evolutionary dynamics of recombination suppression and sex-linked genes
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.09.25.314088
DO 10.1101/2020.09.25.314088
A1 Hanna Sigeman
A1 Maria Strandh
A1 Estelle Proux-Wéra
A1 Verena E. Kutschera
A1 Suvi Ponnikas
A1 Hongkai Zhang
A1 Max Lundberg
A1 Lucile Soler
A1 Ignas Bunikis
A1 Maja Tarka
A1 Dennis Hasselquist
A1 Björn Nystedt
A1 Helena Westerdahl
A1 Bengt Hansson
YR 2020
UL http://biorxiv.org/content/early/2020/09/26/2020.09.25.314088.abstract
AB How the avian sex chromosomes first evolved from autosomes remains elusive as 100 million years (Myr) of divergence and degeneration obscure their evolutionary history. Sylvioidea songbirds is an emerging model for understanding avian sex chromosome evolution because a unique chromosome fusion event ∼24 Myr ago has formed enlarged “neo-sex chromosomes” consisting of an added (new) and an ancestral (old) part. Here, we report the female genome (ZW) of one Sylvioidea species, the great reed warbler (Acrocephalus arundinaceus). We confirm that the added region has been translocated to both Z and W, and show that the added-W part has been heavily reorganised within itself and with the ancestral-W. Next, we show that recombination between Z and W continued after the fusion event, and that recombination suppression took ∼10 Myr to be completed and arose locally and non-linearly along the sex chromosomes. This pattern is inconsistent with that of large inversions and instead suggests gradual and mosaic recombination suppression. We find that the added-W mirrors the ancestral-W in terms of repeat accumulation, loss of genetic variation, and gene degeneration. Lastly, we show that genes being maintained on W are slowly evolving and dosage sensitive, and that highly conserved genes across broad taxonomic groups, regardless of sex-linkage, evolve slower on both Z and W. This study reveals complex expansion of recombination suppression along avian sex chromosomes, and that the evolutionary trajectory of sex-linked genes is highly predictable and governed partly by sex-linkage per se, partly by their functional properties.Competing Interest StatementThe authors have declared no competing interest.