title: Hybrid speciation in sparrows II: a role for sex chromosomes?
abstract: Homoploid hybrid speciation in animals is poorly understood, mainly because of the scarcity of well-documented cases. Here, we present the results of a multilocus sequence analysis on the house sparrow (Passer domesticus), Spanish sparrow (P. hispaniolensis) and their proposed hybrid descendant, the Italian sparrow (P. italiae). The Italian sparrow is shown to be genetically intermediate between the house sparrow and Spanish sparrow, exhibiting genealogical discordance and a mosaic pattern of alleles derived from either of the putative parental species. The average variation on the Z chromosome was significantly reduced compared with autosomal variation in the putative parental species, the house sparrow and Spanish sparrow. Additionally, divergence between the two species was elevated on the Z chromosome relative to the autosomes. This pattern of variation and divergence is consistent with reduced introgression of Z-linked genes and/or a faster-Z effect (increased rate of adaptive divergence on the Z). F(ST) -outlier tests were consistent with the faster-Z hypothesis: two of five Z-linked loci (CHD1Z and PLAA) were identified as candidates for being subject to positive, divergent selection in the putative parental species. Interestingly, the two latter genes showed a mosaic pattern in the (hybrid) Italian sparrow; that is, the Italian sparrow was found to be fixed for Spanish sparrow alleles at CHD1Z and to mainly have house sparrow alleles at PLAA. Preliminary evidence presented in this study thus suggests that sex chromosomes may play a significant role in this case of homoploid hybrid speciation.
authors.affiliation: Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, PO Box 1066, Blindern, N-0316 Oslo, Norway.
authors.forename: Tore O
authors.initials: TO
authors.lastname: Elgvin
authors.forename: Jo S
authors.initials: JS
authors.lastname: Hermansen
authors.forename: Anna
authors.initials: A
authors.lastname: Fijarczyk
authors.forename: Timothée
authors.initials: T
authors.lastname: Bonnet
authors.forename: Thomas
authors.initials: T
authors.lastname: Borge
authors.forename: Stein A
authors.initials: SA
authors.lastname: Saether
authors.forename: Kjetil L
authors.initials: KL
authors.lastname: Voje
authors.forename: Glenn-Peter
authors.initials: GP
authors.lastname: Saetre
mesh_terms: D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D017931:DNA Primers / Q000235:genetics; D005060:Europe; D051456:Gene Flow / Q000235:genetics; D049810:Genetic Speciation; D014644:Genetic Variation; D005828:Genetics, Population; D006239:Haplotypes / Q000235:genetics; D006824:Hybridization, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D011003:Ploidies; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*; D046370:Sparrows / Q000235:genetics*; D013045:Species Specificity
chemical_list: D017931:DNA Primers