Increased divergence but reduced variation on the Z chromosome relative to autosomes in Ficedula flycatchers: differential introgression or the faster‐Z effect?

• Published in: Ecology and evolution Vol. 2; no. 2; pp. 379 - 396
• Main Authors: Hogner, Silje, Sæther, Stein A., Borge, Thomas, Bruvik, Torbjørn, Johnsen, Arild, Sætre, Glenn‐Peter
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.02.2012; John Wiley & Sons, Inc; Wiley
• Subjects: Allopatry; Birds; Chromosomes; congeneric birds; Divergence; Evolution & development; faster‐Z hypothesis; Females; Ficedula; Gene flow; Genes; Genomes; Hypotheses; Males; Mutation; nuclear introns; Original Research; Polymorphism; Population; Z chromosome polymorphism; Z chromosomes; Italy; Spain; congeneric birds; Z chromosome polymorphism; nuclear introns; Allopatry; faster-Z hypothesis
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.92

Recent multilocus studies of congeneric birds have shown a pattern of elevated interspecific divergence on the Z chromosome compared to the autosomes. In contrast, intraspecifically, birds exhibit less polymorphism on the Z chromosome relative to the autosomes. We show that the four black‐and‐white Ficedula flycatcher species show greater genetic divergence on the Z chromosome than on the autosomes, and that the ratios of intraspecific polymorphism at Z‐linked versus autosomal markers are below the neutral expectation of 75%. In all species pairs, we found more fixed substitutions and fewer shared polymorphisms on the Z chromosome than on the autosomes. Finally, using isolation with migration (IMa) models we estimated gene flow among the four closely related flycatcher species. The results suggest that different pattern of evolution of Z chromosomes and autosomes is best explained by the faster‐Z hypothesis, since the estimated long‐term gene flow parameters were close to zero in all comparisons. We show that the four black‐and‐white Ficedula flycatcher species show greater genetic divergence on the Z chromosome than on the autosomes, and that the ratios of intraspecific polymorphism at Z‐linked versus autosomal markers are below the neutral expectation of 75%. Using isolation with migration and population genetic analyses we provide tests of critical predictions from two hypotheses, the faster‐Z hypothesis and differential introgression (reduced rates of introgression on the Z chromosome). Our analyses suggest that we can reject the differential introgression hypothesis, at least in the case of these flycatchers.