title: Independent stratum formation on the avian sex chromosomes reveals inter-chromosomal gene conversion and predominance of purifying selection on the W chromosome.
abstract: We used a comparative approach spanning three species and 90 million years to study the evolutionary history of the avian sex chromosomes. Using whole transcriptomes, we assembled the largest cross-species dataset of W-linked coding content to date. Our results show that recombination suppression in large portions of the avian sex chromosomes has evolved independently, and that long-term sex chromosome divergence is consistent with repeated and independent inversions spreading progressively to restrict recombination. In contrast, over short-term periods we observe heterogeneous and locus-specific divergence. We also uncover four instances of gene conversion between both highly diverged and recently evolved gametologs, suggesting a complex mosaic of recombination suppression across the sex chromosomes. Lastly, evidence from 16 gametologs reveal that the W chromosome is evolving with a significant contribution of purifying selection, consistent with previous findings that W-linked genes play an important role in encoding sex-specific fitness.
authors: Department of Zoology, Edward Grey Institute, University of Oxford, Oxford, OX1 3PS, United Kingdom; Department of Genetics, Evolution and Environment, University College, London, London, WC1E 6BT, United Kingdom. alison.e.wright@ucl.ac.uk.
authors: Alison E
authors: AE
authors: Wright
authors: Peter W
authors: PW
authors: Harrison
authors: Stephen H
authors: SH
authors: Montgomery
authors: Marie A
authors: MA
authors: Pointer
authors: Judith E
authors: JE
authors: Mank
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000145:classification* / Q000235:genetics*; D005260:Female; D005785:Gene Conversion; D008297:Male; D012730:Sex Chromosomes
keywords: Chromosome inversion; female heterogamety; recombination suppression