Contrasting Patterns of Polymorphism and Divergence on the Z Chromosome and Autosomes in Two Ficedula Flycatcher Species

• Published in: Genetics (Austin) Vol. 171; no. 4; pp. 1861 - 1873
• Main Authors: Borge, Thomas, Webster, Matthew T, Andersson, Gunilla, Saetre, Glenn-Peter
• Format: Journal Article
• Language: English
• Published: United States Genetics Soc America 01.12.2005; Genetics Society of America; Copyright © 2005 by the Genetics Society of America
• Subjects: Animal populations; Animals; Base Sequence; Birds; Cluster Analysis; Data analysis; Evolution, Molecular; Ficedula; Ficedula abicollis; Ficedula hypoleuca; Genes; Genetic Speciation; Genetics; Genetics, Population; Haplotypes - genetics; Investigations; Italy; Male; Molecular Sequence Data; Polymorphism, Genetic; Selection, Genetic; Sequence Analysis, DNA; Sex Chromosomes - genetics; Songbirds - genetics; Spain; Italy; Spain
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1534/genetics.105.045120

In geographic areas where pied and collared flycatchers (Ficedula hypoleuca and F. albicollis) breed in sympatry, hybridization occurs, leading to gene flow (introgression) between the two recently diverged species. Notably, while such introgression is observable at autosomal loci it is apparently absent at the Z chromosome, suggesting an important role for genes on the Z chromosome in creating reproductive isolation during speciation. To further understand the role of Z-linked loci in the formation of new species, we studied genetic variation of the two species from regions where they live in allopatry. We analyzed patterns of polymorphism and divergence in introns from 9 Z-linked and 23 autosomal genes in pied and collared flycatcher males. Average variation on the Z chromosome is greatly reduced compared to neutral expectations based on autosomal diversity in both species. We also observe significant heterogeneity between patterns of polymorphism and divergence at Z-linked loci and a relative absence of polymorphisms that are shared by the two species on the Z chromosome compared to the autosomes. We suggest that these observations may indicate the action of recurrent selective sweeps on the Z chromosome during the evolution of the two species, which may be caused by sexual selection acting on Z-linked genes. Alternatively, reduced variation on the Z chromosome could result from substantially higher levels of introgression at autosomal than at Z-linked loci or from a complex demographic history, such as a population bottleneck.