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22 results for “Timema”
Timema genome sequences and annotations. Version 8.
<p>Genome sequence (fasta) files and annotation (gff) files for ten <em>Timema </em>species: <em>T. bartmani, T. cristinae, T. poppensis, T. californicum, T. podura, T. tahoe, T. monikensis, T. douglasi, T. shepardi, and T. genevievae.</em><br> <br> Species are abbreviated as follows: Tbi = <em>T. bartmani</em>, Tce = <em>T. cristinae</em>, Tps = <em>T. poppensis</em>, Tcm = <em>T. californicum</em>, Tpa = <em>T. podura</em>, Tte = <em>T. tahoe</em>, Tms = <em>T. monikensis</em>, Tdi = <em>T. douglasi</em>, Tsi = <em>T. shepardi</em>, and Tge = <em>T. genevievae</em><br> </p> <p>For details of assembly and annotation see: <br> <br> Jaron, K. S*., Parker, D. J*., Anselmetti, Y., Tran Van, P. T., Bast, J., Dumas, Z., Figuet, E., François, C. M., Hayward, K., Rossier, V., Simion, P., Robinson-Rechavi, M., Galtier, N., Schwander, T. 2021. Convergent consequences of parthenogenesis on stick insect genomes. bioRxiv. doi: https://doi.org/10.1101/2020.11.20.391540</p> <p> </p> <p><strong>File list:</strong><br> <br> Tbi_b3v08.fasta = T. bartmani genome sequence file<br> Tbi_b3v08.max_arth_b2g_droso_b2g.gff = T. bartmani genome annotation file<br> Tce_b3v08.fasta = T. cristinae genome sequence file<br> Tce_b3v08.max_arth_b2g_droso_b2g.gff = T. cristinae genome annotation file<br> Tcm_b3v08.fasta = T. bartmani genome sequence file<br> Tcm_b3v08.max_arth_b2g_droso_b2g.gff = T. californicum genome annotation file<br> Tdi_b3v08.fasta = T. douglasi genome sequence file<br> Tdi_b3v08.max_arth_b2g_droso_b2g.gff = T. douglasi genome annotation file<br> Tge_b3v08.fasta = T. genevievae genome sequence file<br> Tge_b3v08.max_arth_b2g_droso_b2g.gff = T. genevievae genome annotation file<br> Tms_b3v08.fasta = T. monikensis genome sequence file<br> Tms_b3v08.max_arth_b2g_droso_b2g.gff = T. monikensis genome annotation file<br> Tpa_b3v08.fasta = T. podura genome sequence file<br> Tpa_b3v08.max_arth_b2g_droso_b2g.gff = T. podura genome annotation file<br> Tps_b3v08.fasta = T. poppensis genome sequence file<br> Tps_b3v08.max_arth_b2g_droso_b2g.gff = T. poppensis genome annotation file<br> Tsi_b3v08.fasta = T. shepardi genome sequence file<br> Tsi_b3v08.max_arth_b2g_droso_b2g.gff = T. shepardi genome annotation file<br> Tte_b3v08.fasta = T. tahoe genome sequence file<br> Tte_b3v08.max_arth_b2g_droso_b2g.gff = T. tahoe genome annotation file</p>
Data from: Disruptive selection and the evolution of discrete color morphs in Timema stick insects
<p>A major unresolved issue in biology is why phenotypic and genetic variation is sometimes continuous, yet other times packaged into discrete units of diversity, such as morphs, ecotypes, and species. In theory, ecological discontinuities can impose strong disruptive selection that promotes the evolution of discrete forms, but direct tests of this hypothesis are lacking. Here we show that <span><em>Timema</em> </span>stick insects exhibit genetically-determined color morphs that range from weakly to strongly discontinuous. Color data from nature and a manipulative field experiment demonstrate that greater morph differentiation is associated with shifts from host plants exhibiting more continuous color variation to those exhibiting greater coloration distance between green leaves and brown stems, the latter of which generates strong disruptive selection. Our results show how ecological factors can promote discrete variation, and we further present results on how this can have variable effects on the genetic differentiation that promotes speciation.</p>
Data from: Disruptive selection and the evolution of discrete color morphs in Timema stick insects
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Adaptive zones shape the magnitude of premating reproductive isolation in Timema stick insects
<p>Simpson's fossil-record inspired model of 'adaptive zones' proposes that evolution is dominated by small fluctuations within adaptive zones, occasionally punctuated by larger shifts between zones. This model can help explain why the process of population divergence often results in weak or moderate reproductive isolation (RI), rather than strong RI and distinct species. Applied to the speciation process, the adaptive zones hypothesis makes two inter-related predictions: (i) large shifts between zones are relatively rare, (ii) when large shifts do occur they generate stronger RI than shifts within zones. Here we use ecological, phylogenetic, and behavioural data to test these predictions in <i>Timema </i>stick insects. We show that host use in <i>Timema</i> is dominated by moderate shifts within the systematic divisions of flowering plants and conifers, with only a few extreme shifts between these divisions. However, when extreme shifts occur they generate greater RI than do more moderate shifts. Our results support the adaptive zones model, and suggest that the net contribution of ecological shifts to diversification is dependent on both their magnitude and frequency. We discuss the generality of our findings in light of emerging evidence from diverse taxa that the evolution of RI is not always the only factor determining the origin of species diversity</p>
Timema_project
Heaviest intermediate files producted during the analyses on the evolution of parthenogenesis in Timema stick insects
Data for: Testing for fitness epistasis in a transplant experiment identifies a candidate adaptive locus in Timema stick insects
<p>Identifying the genetic basis of adaptation is a central goal of evolutionary biology. However, identifying genes and mutations affecting fitness remains challenging because a large number of traits and variants can influence fitness. Selected phenotypes can also be difficult to know <em>a priori</em>, complicating top-down genetic approaches for trait mapping that involve crosses or genome-wide association studies. In such cases, experimental genetic approaches, where one maps fitness directly and attempts to infer the traits involved afterward, can be valuable. Here, we re-analyse data from a transplant experiment involving <em>Timema</em> stick insects, where five physically clustered SNPs associated with cryptic body colouration were shown to interact to affect survival. Our analysis covers a larger genomic region than past work and revealed a locus previously not identified as associated with survival. This locus resides near a gene, <em>Punch</em> (<em>Pu</em>), involved in pteridine pigments production, implying that it could be associated with an unmeasured colouration trait. However, by combining previous and newly obtained phenotypic data, we show that this trait is not eye or body colouration. We discuss the implications of our results for the discovery of traits, genes, and mutations associated with fitness in other systems, as well as for supergene evolution.</p>
Climatic similarity and genomic background shape the extent of parallel adaptation in Timema stick insects
<p>Evolution can repeat itself, resulting in parallel adaptations in independent lineages occupying similar environments. Moreover, parallel evolution sometimes, but not always, uses the same genes. Two main hypotheses have been put forth to explain the probability and extent of parallel evolution. First, parallel evolution is more likely when shared ecologies result in similar patterns of natural selection in different taxa. Second, parallelism is more likely when genomes are similar, because of shared standing variation and similar mutational effects in closely related genomes. Here we combine ecological, genomic, experimental, and phenotypic data with Bayesian modeling and randomization tests to quantify the degree of parallelism and its relationship with ecology and genetics. Our results show that the extent to which genomic regions associated with climate are parallel among species of <em>Timema</em> stick insects is shaped collectively by shared ecology and genomic background. Specifically, the extent of genomic parallelism decays with divergence in climatic conditions (i.e., habitat or ecological similarity) and genomic similarity. Moreover, we find that climate-associated loci are likely subject to selection in a field experiment, overlap with genetic regions associated with cuticular hydrocarbon traits, and are not strongly shaped by introgression between species. Our findings shed light on when evolution is most expected to repeat itself.</p>
Adaptive zones shape the magnitude of premating reproductive isolation in Timema stick insects
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Climatic similarity and genomic background shape the extent of parallel adaptation in Timema stick insects
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Data for: Testing for fitness epistasis in a transplant experiment identifies a candidate adaptive locus in Timema stick insects
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Data from: Genome-wide association mapping of phenotypic traits subject to a range of intensities of natural selection in Timema cristinae
The genetic architecture of adaptive traits can reflect the evolutionary history of populations and also shape divergence among populations. Despite this central role in evolution, relatively little is known regarding the genetic architecture of adaptive traits in nature, particularly for traits subject to known selection intensities. Here we quantitatively describe the genetic architecture of traits that are subject to known intensities of differential selection between host plant species in Timema cristinae stick insects. Specifically, we used phenotypic measurements of 10 traits and 211,004 single-nucleotide polymorphisms (SNPs) to conduct multilocus genome-wide association mapping. We identified a modest number of SNPs that were associated with traits and sometimes explained a large proportion of trait variation. These SNPs varied in their strength of association with traits, and both major and minor effect loci were discovered. However, we found no relationship between variation in levels of divergence among traits in nature and variation in parameters describing the genetic architecture of those same traits. Our results provide a first step toward identifying loci underlying adaptation in T. cristinae. Future studies will examine the genomic location, population differentiation, and response to selection of the trait-associated SNPs described here.
Data from: The role of structural genomic variants in population differentiation and ecotype formation in Timema cristinae walking sticks
Theory predicts that structural genomic variants such as inversions can promote adaptive diversification and speciation. Despite increasing empirical evidence that adaptive divergence can be triggered by one or a few large inversions, the degree to which widespread genomic regions under divergent selection are associated with structural variants remains unclear. Here we test for an association between structural variants and genomic regions that underlie parallel host-plant associated ecotype formation in Timema cristinae stick insects. Using mate-pair re-sequencing of 20 new whole genomes we find that modest-sized structural variants such as inversions, deletions, and duplications are widespread across the genome, being retained as standing variation within and among populations. Using 160 previously published, standard-orientation whole genome sequences we find little to no evidence that the DNA sequences within inversions exhibit accentuated differentiation between ecotypes. In contrast, a formerly described large region of reduced recombination that harbors genes controlling color-pattern exhibits evidence for accentuated differentiation between ecotypes, which is consistent with differences in the frequency of color-pattern morphs between host-associated ecotypes. Our results suggest that some types of structural variants (e.g., large inversions) are more likely to underlie adaptive divergence than others, and that structural variants are not required for subtle yet genome-wide genetic differentiation with gene flow.
Data from: De novo characterization of the Timema cristinae transcriptome facilitates marker discovery and inference of genetic divergence.
Adaptation to different ecological environments can promote speciation. Although numerous examples of such 'ecological speciation' exist, the genomic basis of the process, and the role of gene flow in it, remains less understood. This is, at least in part, because systems that are well characterized in terms of their ecology often lack genomic resources. In this study we characterize the transcriptome of Timema cristinae stick insects, a system that has been researched intensively in terms of ecological speciation, but for which genomic resources have not been previously developed. Specifically, we obtained >1 million 454 sequencing reads that assembled into 84,937 contigs representing approximately 18,282 unique genes and tens of thousands of potential molecular markers. Second, as an illustration of their utility, we used these genomic resources to assess multi-locus genetic divergence within both an ecotype pair and a species pair of Timema stick insects. The results suggest variable levels of genetic divergence and gene flow among taxon pairs and genes and illustrate a first step towards future genomic work in Timema.
Data from: De novo characterization of the Timema cristinae transcriptome facilitates marker discovery and inference of genetic divergence.
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Data from: Genome-wide association mapping of phenotypic traits subject to a range of intensities of natural selection in Timema cristinae
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Data from: The role of structural genomic variants in population differentiation and ecotype formation in Timema cristinae walking sticks
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Data from: Color phenotypes are under similar genetic control in two distantly related species of Timema stick insect
Ecology and genetics are both of general interest to evolutionary biologists as they can influence the phenotypic and genetic response to selection. The stick insects Timema podura and T. cristinae exhibit a green/melanistic body color polymorphism that is subject to different ecologically-based selective regimes in the two species. Here we describe aspects of the genetics of this color polymorphism in T. podura, and compare this to previous results in T. cristinae. We first show that similar color phenotypes of the two species cluster in phenotypic space. We then use genome-wide association mapping to show that in both species, color is controlled by few loci, dominance relationships between color alleles are the same, and SNPs associated with color phenotypes co-localize to the same linkage group. Regions within this linkage group that harbor genetic variants associated with color exhibit elevated linkage disequilibrium relative to genome wide expectations, but more strongly so in T. cristinae. We use these results to discuss predictions regarding how the genetics of color could influence levels of phenotypic and genetic variation that segregate within and between populations of T. podura and T. cristinae, drawing parallels with other organisms.
Timema_project_discard
Timemaproject
Data from: Color phenotypes are under similar genetic control in two distantly related species of Timema stick insect
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Data from: Natural selection and the predictability of evolution in Timema stick insects
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