title: Patterns of molecular evolution of an avian neo-sex chromosome.
abstract: Newer parts of sex chromosomes, neo-sex chromosomes, offer unique possibilities for studying gene degeneration and sequence evolution in response to loss of recombination and population size decrease. We have recently described a neo-sex chromosome system in Sylvioidea passerines that has resulted from a fusion between the first half (10 Mb) of chromosome 4a and the ancestral sex chromosomes. In this study, we report the results of molecular analyses of neo-Z and neo-W gametologs and intronic parts of neo-Z and autosomal genes on the second half of chromosome 4a in three species within different Sylvioidea lineages (Acrocephalidea, Timaliidae, and Alaudidae). In line with hypotheses of neo-sex chromosome evolution, we observe 1) lower genetic diversity of neo-Z genes compared with autosomal genes, 2) moderate synonymous and weak nonsynonymous sequence divergence between neo-Z and neo-W gametologs, and 3) lower GC content on neo-W than neo-Z gametologs. Phylogenetic reconstruction of eight neo-Z and neo-W gametologs suggests that recombination continued after the split of Alaudidae from the rest of the Sylvioidea lineages (i.e., after ~42.2 Ma) and with some exceptions also after the split of Acrocephalidea and Timaliidae (i.e., after ~39.4 Ma). The Sylvioidea neo-sex chromosome shares classical evolutionary features with the ancestral sex chromosomes but, as expected from its more recent origin, shows weaker divergence between gametologs.
authors: Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden. irene.pala@biol.lu.se
authors: Irene
authors: I
authors: Pala
authors: Dennis
authors: D
authors: Hasselquist
authors: Staffan
authors: S
authors: Bensch
authors: Bengt
authors: B
authors: Hansson
mesh_terms: D000818:Animals; D001482:Base Composition / Q000235:genetics; D001483:Base Sequence; D016000:Cluster Analysis; D019143:Evolution, Molecular; D005796:Genes / Q000235:genetics*; D005819:Genetic Markers / Q000235:genetics; D014644:Genetic Variation; D007438:Introns / Q000235:genetics; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D046109:Passeriformes / Q000235:genetics*; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*; D013045:Species Specificity
chemical_list: D005819:Genetic Markers