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29 results for “Chromosome Z”
Pronounced differentiation on the Z chromosome and parts of the autosomes in crowned sparrows contrasts with mitochondrial paraphyly: implications for speciation
<p>When a single species evolves into multiple descendent species, some parts of the genome can play a key role in the evolution of reproductive isolation while other parts flow between the evolving species via interbreeding. Genomic evolution during the speciation process is particularly interesting when major components of the genome—for instance, sex chromosomes vs. autosomes vs. mitochondrial DNA—show widely differing patterns of relationships between three diverging populations. The golden-crowned sparrow (<em>Zonotrichia atricapilla</em>) and the white-crowned sparrow (<em>Zonotrichia leucophrys</em>) are phenotypically differentiated sister species that are largely reproductively isolated despite possessing similar mitochondrial genomes, likely due to recent introgression. We assessed variation in more than 45,000 single nucleotide polymorphisms (SNPs) to determine the structure of nuclear genomic differentiation between these species and between two hybridizing subspecies of <em>Z. leucophrys</em>. The two <em>Z. leucophrys</em> subspecies showed moderate levels of relative differentiation and patterns consistent with a history of recurrent selection in both ancestral and daughter populations, with much of the sex chromosome Z and a large region on the autosome 1A showing increased differentiation compared to the rest of the genome. The two species <em>Z. leucophrys</em> and <em>Z. atricapilla</em> show high relative differentiation and strong heterogeneity in the level of differentiation among various chromosomal regions, with a large portion of the sex chromosome (Z) showing highly divergent haplotypes between these species. Studies of speciation often emphasize mitochondrial DNA differentiation, but speciation between <em>Z. atricapilla</em> and <em>Z. leucophrys</em> appears primarily associated with Z chromosome divergence and more moderately associated with autosomal differentiation, whereas mitochondria appear highly similar due apparently to recent introgression. These results add to the growing body of evidence for highly heterogeneous patterns of genomic differentiation during speciation, with some genomic regions showing lack of gene flow between populations many hundreds of thousands of years before other genomic regions.</p>
Data from: Chromosome-scale assembly with a phased sex-determining region resolves features of early Z and W chromosome differentiation in a wild octoploid strawberry
<p>Abstract: When sex chromosomes stop recombining, they start to accumulate differences. The sex-limited chromosome (Y or W) especially is expected to degenerate via the loss of nucleotide sequence and the accumulation of repetitive sequences. However, how early signs of degeneration can be detected in a new sex chromosome is still unclear. The sex determining region (SDR) of the octoploid strawberries is young, small, and dynamic. Using PacBio HiFi reads, we obtained a chromosome scale assembly of a female (ZW) <em>Fragaria chiloensis</em> plant carrying the youngest and largest of the known SDR on the W in strawberries. We fully characterized the previously incomplete SDR, confirming its gene content, genomic location and evolutionary history. Resolution of gaps in the previous characterization of the SDR added 10 kbp of sequence including a non-canonical LTR-retrotransposon; whereas the Z sequence revealed a <em>Harbinger</em> transposable element adjoining the SDR insertion site. Limited genetic differentiation of the sex chromosomes coupled with structural variation may indicate an early stage of W degeneration. The sex chromosomes have a similar percentage of repeats but differ in their repeat distribution. Differences in the pattern of repeats (transposable element polymorphism) apparently precede sex chromosome differentiation, thus potentially contributing to recombination cessation as opposed to being a consequence of it.</p> <p>Repository content: data (sequence alignments, phylogenetic trees, genome assembly, and vcf files) and scripts associated with the manuscript "Chromosome-scale assembly with a phased sex-determining region resolves features of early Z and W chromosome differentiation in a wild octoploid strawberry"</p>
Pronounced differentiation on the Z chromosome and parts of the autosomes in crowned sparrows contrasts with mitochondrial paraphyly: implications for speciation
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Chromosome-level assemblies of the Pieris mannii butterfly genome suggest Z-origin and rapid evolution of the W chromosome
<p><span>The insect order Lepidoptera (butterflies and moths) represents the largest group of organisms with ZW/ZZ sex determination. While the origin of the Z chromosome predates the evolution of the Lepidoptera, the W chromosomes are considered younger, but their origin is debated. To shed light on the origin of the lepidopteran W, we here produce chromosome-level genome assemblies for the butterfly <em>Pieris</em> <em>mannii</em>, and compare the sex chromosomes within and between <em>P. mannii </em>and its sister species <em>P. rapae</em>. Our analyses clearly indicate a common origin of the W chromosomes of the two <em>Pieris</em> species, and reveal similarity between the Z and W in chromosome sequence and structure. This supports the view that the W in these species originates from Z-autosome fusion rather than from a redundant B chromosome. We further demonstrate the extremely rapid evolution of the W relative to the other chromosomes and argue that this may preclude reliable conclusions about the origins of W chromosomes based on comparisons among distantly related Lepidoptera. Finally, we find that sequence similarity between the Z and W chromosomes is greatest toward the chromosome ends, perhaps reflecting selection for the maintenance of recognition sites essential to chromosome segregation. Our study highlights the utility of long-read sequencing technology for illuminating chromosome evolution.</span></p>
Chromosome-level assemblies of the Pieris mannii butterfly genome suggest Z-origin and rapid evolution of the W chromosome
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Data from: Impact of Z chromosome inversions on gene expression in testes and liver tissues in the zebra finch
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Data from: Sexually-selected differences in warbler plumage are related to a putative inversion on the Z chromosome
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Data from: Footprints of adaptive evolution revealed by whole Z chromosomes haplotypes in flycatchers
Detecting positive selection using genomic data is critical to understanding the role of adaptive evolution. Of particular interest in this context is sex chromosomes since they are thought to play a special role in local adaptation and speciation. We sought to circumvent the challenges associated with statistical phasing when using haplotype-based statistics in sweep scans by benefitting from that whole-chromosome haplotypes of the sex chromosomes can be obtained by re-sequencing of individuals of the hemizygous sex. We analyzed whole Z chromosome haplotypes from 100 females from several populations of four black and white flycatcher species (in birds, females are ZW and males ZZ). Based on integrated haplotype score (iHS) and number of segregating sites by length (nSL) statistics, we found strong and frequent haplotype structure in several regions of the Z chromosome in each species. Most of these sweep signalswere population-specific, with essentially no evidence for regions under selection shared among species. Some completed sweeps were revealed by the cross-population extended haplotype homozygosity (XP-EHH) statistic. Importantly, by using statistically phased Z chromosome data from re-sequencing of males, we failed to recover the signals of selection detected in analyses based on whole-chromosome haplotypes from females; instead, what likely represent false signals of selection were frequently seen. This highlights the power issues in statistical phasing and cautions against conclusions from selection scans using such data. The detection of frequent selective sweeps on the avian Z chromosome supports a large role of sex chromosomes in adaptive evolution.
Data from: Recent speciation and elevated Z-chromosome differentiation between sexually monochromatic and dichromatic species of Australian teals
Sex chromosomes potentially have an important role in speciation and often have elevated differentiation between closely related species. In birds, traits associated with male plumage, female mate preference, and hybrid fitness have been linked to the Z-chromosome (females are heterogametic, ZW). We tested for elevated Z-differentiation between two recently diverged species of Australian ducks, the sexually monochromatic grey teal Anas gracilis and the dichromatic chestnut teal A. castanea. Despite prominent morphological differences, these two species are genetically indistinguishable at both mitochondrial DNA (mean ΦST < 0.0001) and 17 autosomal loci (mean ΦST = 0.0056). However, we detected elevated Z-differentiation (mean ΦST = 0.281) and tentative evidence of an island of differentiation on the Z-chromosome. This elevated differentiation was explained by a high frequency of derived alleles in chestnut teal that were absent in grey teal, which parallels independent evidence for a gain in dichromatism from a monochromatic ancestor. Coalescent estimates of demographic history and simulations indicated that the elevated Z-differentiation was unlikely to be explained by neutral processes, but instead supported a role of divergent selection. We discuss evidence for models of speciation with gene flow versus adaptive divergence in the absence of gene flow and find that both hypotheses are plausible explanations of the data. Overall, these teal have the weakest background differentiation documented to date for a species showing a large Z-effect, and they are an excellent model species for studying speciation genomics and the evolution of sexual dichromatism.
Data from: Whole-genome phylogeography of the Blue-faced honeyeater (Entomyzon cyanotis) and discovery and characterization of a neo-Z chromosome
<p>Whole-genome surveys of genetic diversity and geographic variation often yield unexpected discoveries of novel structural variation, which long-read DNA sequencing can help clarify. Here we report on whole-genome phylogeography of a bird exhibiting classic vicariant geographies across Australia and New Guinea, the Blue-faced honeyeater (<em>Entomyzon cyanotis</em>), and the discovery and characterization of a novel neo-Z chromosome by long-read sequencing. Using short-read genome-wide SNPs, we inferred population divergence events within <em>E. cyanotis</em> across the Carpentarian and other biogeographic barriers during the Pleistocene (~0.3 – 1.7 MYA). Evidence for introgression between non-sister populations supports a hypothesis of reticulate evolution around a triad of dynamic barriers around Pleistocene Lake Carpentaria between Australia and New Guinea. During this phylogeographic survey, we discovered a large (134 Mbp) neo-Z chromosome and explore its diversity, divergence and introgression landscape. We show that, as in some Sylvioid passerine birds, a fusion occurred between chromosome 5 and the Z chromosome to form a neo-Z chromosome, with the ancestral pseudoautosomal region (PAR) appearing to become non-recombinant between Z and W, along with most of the fused chromosome 5 (~37.2 Mbp). The added non-recombinant portion of the neo-Z displays reduced heterozygosity and faster population genetic differentiation compared with the ancestral Z. Yet, the new PAR shows elevated diversity and reduced differentiation compared to autosomes, potentially resulting from introgression. In our case, long-read sequencing helped clarify the genomic landscape of population divergence on autosomes and sex chromosomes in a species where prior knowledge of genome structure was still incomplete.</p>
Data from: Z chromosome divergence, polymorphism, and relative effective population size in a genus of lekking birds
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Data from: Whole-genome phylogeography of the Blue-faced honeyeater (Entomyzon cyanotis) and discovery and characterization of a neo-Z chromosome
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Data from: Footprints of adaptive evolution revealed by whole Z chromosomes haplotypes in flycatchers
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Data from: Recent speciation and elevated Z-chromosome differentiation between sexually monochromatic and dichromatic species of Australian teals
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Data from: Evidence of linked selection on the Z chromosome of hybridizing hummingbirds
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Genome-wide SNP analysis of Siamese cobra (Naja kaouthia) reveals the molecular basis of transitions between Z and W sex chromosomes and supports the presence of an ancestral super-sex chromosome in amniotes
<p>Elucidation of the process of sex chromosome differentiation is necessary to understand the dynamics of evolutionary mechanisms in organisms. The Siamese cobra (<i>Naja kaouthia</i>) exhibits ZZ/ZW heteromorphic sex chromosomes. The W sex chromosome contains a large number of repeats and shares several amniote sex chromosomal linkages. In conjunction with recent advances in high-throughput sequencing, Diversity Arrays Technology (DArTseq™) provides an effective approach to identify sex-specific loci that are epoch-making, to understand the dynamics of molecular transitions between the Z and W sex chromosomes in a snake lineage. From a total of 543 perfectly sex-linked loci, 90 loci showed partial homology with several amniote sex chromosomal linkages, and 89 loci were homologous to transposable elements, which suggests that recombination suppression may be the crucial step in snake sex chromosome differentiation. Two loci were confirmed as W-specific nucleotides in females but not in males in the population examined by PCR amplification; one of the two loci (locus id: 100002617) was further amplified in females of the Indochinese spitting cobra (<i>N. siamensis</i>) but not in the other 22 snake species examined. Female-specific DArT markers were identified in Siamese cobra. These loci might result from a sex chromosome differentiation process between Z and W and involve putative sex-determination regions in Siamese cobra. Short sequences derived from DArTseq™ technology also shared linkage homologies among amniote sex chromosomes, which supports the hypothesis of an ancestral super-sex chromosome with overlaps of partial sex chromosomal linkages. The locus (id: 100002617) shared in <i>N. kaouthia</i> and <i>N. siamensis</i>, but among 22 other snake species, indicates inheritance from a common ancestor as synapomorphic loci in the <i>Naja</i> lineage. The ease of use of the DArT markers and DArTseq™ platform provides a useful strategy for future research on sex chromosome evolution in snakes.</p>
Data from: Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards
Speciation is a continuous and dynamic process, and studying organisms during the early stages of this process can aid in identifying speciation mechanisms. The mallard (Anas platyrhynchos) and Mexican duck (A. [p.] diazi) are two recently diverged taxa with a history of hybridization and controversial taxonomy. To understand their evolutionary history, we conducted genomic scans to characterize patterns of genetic diversity and divergence across the mitochondrial DNA (mtDNA) control region, 3523 autosomal loci and 172 Z-linked sex chromosome loci. Between the two taxa, Z-linked loci (ΦST = 0.088) were 5.2 times more differentiated than autosomal DNA (ΦST = 0.017) but comparable to mtDNA (ΦST = 0.092). This elevated Z differentiation deviated from neutral expectations inferred from simulated data that incorporated demographic history and differences in effective population sizes between marker types. Furthermore, 3% of Z-linked loci, compared to <0.1% of autosomal loci, were detected as outlier loci under divergent selection with elevated relative (ΦST) and absolute (dXY) estimates of divergence. In contrast, the ratio of Z-linked and autosomal differentiation among the seven Mexican duck sampling locations was close to 1:1 (ΦST = 0.018 for both markers). We conclude that between mallards and Mexican ducks, divergence at autosomal markers is largely neutral, whereas greater divergence on the Z chromosome (or some portions thereof) is likely the product of selection that has been important in speciation. Our results contribute to a growing body of literature indicating elevated divergence on the Z chromosome and its likely importance in avian speciation.
Sex-specific splicing of Z- and W-borne nr5a1 alleles suggests sex determination is controlled by chromosome conformation
<p><i>Pogona vitticeps</i> has female heterogamety (ZZ/ZW) but the master sex determining gene is unknown, as is the case for all reptiles. We show that <i>nr5a1</i>, a gene that is essential in mammalian sex determination, has alleles on the Z and W chromosomes (Z-<i>nr5a1</i> and W-<i>nr5a1</i>), which are both expressed and can recombine. Three transcript isoforms of Z-<i>nr5a1</i> were detected in gonads of adult ZZ males, two of which encode a functional protein. However, ZW females produced sixteen isoforms, most of which contained premature stop codons. The array of transcripts produced by the W-borne allele (W-<i>nr5a1</i>) is likely to produce truncated polypeptides that could act as a competitive inhibitor to the full-length intact protein. We hypothesize that an altered configuration of the W chromosomes affects the conformation of the primary transcript generating inhibitory W-borne isoforms that suppress testis determination. Under this hypothesis, the GSD system of <i>P. vitticeps</i> is a W-borne dominant female-determiner that may be controlled epigenetically.</p>
Supplementary material 1 from: Lin C-X, Xu G-L, Jin Z-F, Liao W-B, Xu K-W (2022) Molecular, chromosomal, and morphological evidence reveals a new allotetraploid fern species of Asplenium (Aspleniaceae) from southern Jiangxi, China. PhytoKeys 199: 113-127. https://doi.org/10.3897/phytokeys.199.81292
Table S1
Fig. 6. Z in Interspecific chromosomal divergences in the genus Characidium (Teleostei: Characiformes: Crenuchidae)
Fig. 6. Z an W sex chromosomes of the Characidium species analyzed in this study, after C-banding (first row) and silver nitrate staining (second row). Note the different distribution of the heterochromatin, mainly in the W chromosome in (a) C. schubarti, (b), Characidium sp., (c) C. pterostictum, (d) C. oiticicai, (e) C. lanei, and (f) C. lauroi.
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