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Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 65,227 bioRxiv papers from 288,972 authors.

Most downloaded bioRxiv papers, since beginning of last month

in category evolutionary biology

4,291 results found. For more information, click each entry to expand.

1: A geostatistical approach to modelling human Holocene migrations in Europe using ancient DNA
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Posted to bioRxiv 31 Oct 2019

A geostatistical approach to modelling human Holocene migrations in Europe using ancient DNA
937 downloads evolutionary biology

Fernando Racimo, Jessie Woodbridge, Ralph Fyfe, Martin Sikora, Karl-Goran Sjogren, Kristian Kristiansen, Marc Vander Linden

The European continent was subject to two major migrations of peoples during the Holocene: the northwestward movement of Anatolian farmer populations during the Neolithic and the westward movement of Yamnaya steppe peoples during the Bronze Age. These movements changed the genetic composition of the continent's inhabitants, via admixture and population replacement processes. The Holocene was also characterized by major changes in vegetation composition, which altered the environment occupied by the original hunter-gatherer populations. Here, we use a combination of paleogenomics and geostatistical modelling to produce detailed maps of the movement of these populations over time and space, and to understand how these movements impacted the European vegetation landscape. We find that the dilution of hunter-gatherer ancestries and the Yamnaya steppe migration coincided with a reduction in the amount of broad-leaf forest and an increase in the amount of pasture lands in the continent. We also show that climate played a role in these vegetational changes. Additionally, we find that the spread of Neolithic farmer ancestry had a two-pronged wavefront, in agreement with similar findings based on patterns of the cultural spread of farming from radiocarbon-dated archaeological sites. With thousands of ancient genomes publicly available and in production, we foresee that the integration of ancient DNA with geostatistical techniques and large-scale archaeological datasets will revolutionize the study of ancient populations movements, and their effects on local fauna and flora.

2: Polygenic adaptation after a sudden change in environment
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Posted to bioRxiv 03 Oct 2019

Polygenic adaptation after a sudden change in environment
780 downloads evolutionary biology

Laura Katharine Hayward, Guy Sella

Polygenic adaptation in response to selection on quantitative traits is thought to be ubiquitous in humans and other species, yet this mode of adaptation remains poorly understood. We investigate the dynamics of this process, assuming that a sudden change in environment shifts the optimal value of a highly polygenic quantitative trait. We find that when the shift is not too large relative to the genetic variance in the trait and this variance arises from segregating loci with small to moderate effect sizes (defined in terms of the selection acting on them before the shift), the mean phenotype's approach to the new optimum is well approximated by a rapid exponential process first described by Lande (1976). In contrast, when the shift is larger or large effect loci contribute substantially to genetic variance, the initially rapid approach is succeeded by a much slower one. In either case, the underlying changes to allele frequencies exhibit different behaviors short and long-term. Over the short term, strong directional selection on the trait introduces small differences between the frequencies of minor alleles whose effects are aligned with the shift in optimum versus those with effects in the opposite direction. The phenotypic effects of these differences are dominated by contributions from alleles with moderate and large effects, and cumulatively, these effects push the mean phenotype close to the new optimum. Over the longer term, weak directional selection on the trait can amplify the expected frequency differences between opposite alleles; however, since the mean phenotype is close to the new optimum, alleles are mainly affected by stabilizing selection on the trait. Consequently, the frequency differences between opposite alleles translate into small differences in their probabilities of fixation, and the short-term phenotypic contributions of large effect alleles are largely supplanted by contributions of fixed, moderate ones. This process takes on the order of ~4Ne generations (where Ne is the effective population size), after which the steady state architecture of genetic variation around the new optimum is restored.

3: Massive haplotypes underlie ecotypic differentiation in sunflowers
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Posted to bioRxiv 02 Oct 2019

Massive haplotypes underlie ecotypic differentiation in sunflowers
669 downloads evolutionary biology

Marco Todesco, Gregory L. Owens, Natalia Bercovich, Jean-Sebastien Legare, Shaghayegh Soudi, Dylan O. Burge, Kaichi Huang, Kate L Ostevik, Emily B. M. Drummond, Ivana Imerovski, Kathryn Lande, Mariana A. Pascual, Winnie Cheung, S. Evan Staton, Stephane Munos, Rasmus Nielsen, Lisa A Donovan, John M Burke, Sam Yeaman, Loren H. Rieseberg

Species often include multiple ecotypes that are adapted to different environments. But how do ecotypes arise, and how are their distinctive combinations of adaptive alleles maintained despite hybridization with non-adapted populations? Re-sequencing of 1506 wild sunflowers from three species identified 37 large (1-100 Mbp), non-recombining haplotype blocks associated with numerous ecologically relevant traits, and soil and climate characteristics. Limited recombination in these regions keeps adaptive alleles together, and we find that they differentiate several sunflower ecotypes; for example, they control a 77 day difference in flowering between ecotypes of silverleaf sunflower (likely through deletion of a FLOWERING LOCUS T homolog), and are associated with seed size, flowering time and soil fertility in dune-adapted sunflowers. These haplotypes are highly divergent, associated with polymorphic structural variants, and often appear to represent introgressions from other, possibly extinct, congeners. This work highlights a pervasive role of structural variation in maintaining complex ecotypic adaptation.

4: Estimating the genome-wide contribution of selection to temporal allele frequency change
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Posted to bioRxiv 09 Oct 2019

Estimating the genome-wide contribution of selection to temporal allele frequency change
659 downloads evolutionary biology

Vince Buffalo, Graham Coop

Rapid phenotypic adaptation is often observed in natural populations and selection experiments. However, detecting the genome-wide impact of this selection is difficult, since adaptation often proceeds from standing variation and selection on highly polygenic traits, both of which may leave faint genomic signals indistinguishable from a noisy background of genetic drift. One promising signal comes from the genome-wide covariance between allele frequency changes observable from temporal genomic data, e.g. evolve-and-resequence studies. These temporal covariances reflect how the change in neutral allele frequency at one timepoint is predictive of the changes at later timepoints when there is heritable fitness variation in the population, as neutral alleles can remain associated with selected alleles over time. Since genetic drift does not lead to temporal covariance, we can use these covariances to estimate what fraction of the variation in allele frequency change through time is driven by linked selection. Here, we reanalyze two Drosophila simulans evolve-and-resequence studies, and one artificial selection experiment in mice, to quantify the effects of linked selection over short timescales using covariance among time-points and across replicates. We estimate that at least 17% to 37% of allele frequency change is driven by selection in these experiments. Against this background of positive genome-wide temporal covariances we also identify signals of negative temporal covariance corresponding to reversals in the direction of selection for a reasonable proportion of loci over the time course of a selection experiment. Overall, we find that in the three studies we analyzed, linked selection has a large impact on short-term allele frequency dynamics that is readily distinguishable from genetic drift.

5: Inference of population genetic structure from temporal samples of DNA
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Posted to bioRxiv 10 Oct 2019

Inference of population genetic structure from temporal samples of DNA
451 downloads evolutionary biology

Olivier Francois, Séverine Liégeois, Benjamin Demaille, Flora Jay

The recent years have seen a growing number of studies investigating evolutionary questions using ancient DNA techniques and temporal samples of DNA. To address these questions, one of the most frequently-used algorithm is based on principal component analysis (PCA). When PCA is applied to temporal samples, the sample dates are, however, ignored during analysis, which could lead to some misinterpretations of the results. Here we introduce a new factor analysis (FA) method for which individual scores are corrected for the effect of allele frequency drift through time. Based on a diffusion approximation, our approach approximates allele frequency drift in a random mating population by a Brownian process. Exact solutions for estimates of corrected factors are obtained, and a fast estimation algorithm is presented. We compared data representations obtained from the FA method with PCA and with PC projections in simulations of divergence and admixture scenarios. Then we applied FA with correction for temporal drift to study the evolution of hepatitis C virus in a patient infected by multiple strains, and to describe the population structure of ancient European samples.

6: Shifting spaces: which disparity or dissimilarity metrics best summarise occupancy in multidimensional spaces?
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Posted to bioRxiv 11 Oct 2019

Shifting spaces: which disparity or dissimilarity metrics best summarise occupancy in multidimensional spaces?
438 downloads evolutionary biology

Thomas Guillerme, Mark N Puttick, Ariel E Marcy, Vera Weisbecker

Multidimensional analysis of traits are now a common toolkit in ecology and evolution and are based on trait-spaces in which each dimension summarise the observed trait combination (a morphospace or an ecospace). Observations of interest will typically occupy a subset of this trait-space, and researchers will apply one or more metrics to quantify the way in which organisms "inhabit" that trait-space. In macroevolution and ecology these metrics are referred to as disparity or dissimilarity metrics and can be generalised as space occupancy metrics. Researchers use these metrics to investigate how space occupancy changes through time, in relation to other groups of organisms, and in response to global environmental changes, such as global warming events or mass extinctions. However, the mathematical and biological meaning of most space occupancy metrics is vague with the majority of widely-used metrics lacking formal description. Here we propose a broad classification of space occupancy metrics into three categories that capture changes in volume, density, or position. We analyse the behaviour of 25 metrics to study changes in trait-space volume, density and position on a series of simulated and empirical datasets. We find no one metric describes all of trait-space but that some metrics are better at capturing certain aspects compared to other approaches and that their performance depends on both the trait-space and the hypothesis analysed. However, our results confirm the three broad categories (volume, density and position) and allow to relate changes in any of these categories to biological phenomena. Since the choice of space occupancy metric should be specific to the data and question at had, we introduced \['moms'\](https://tguillerme.shinyapps.io/moms/), a user-friendly tool based on a graphical interface that allows users to both visualise and measure changes space occupancy for any metric in simulated or imported trait-spaces. Users are also provided with tools to transform their data in space (e.g. contraction, displacement, etc.). This tool is designed to help researchers choose the right space occupancy metrics, given the properties of their trait-space and their biological question.

7: The origin of the central dogma through conflicting multilevel selection
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Posted to bioRxiv 09 Jan 2019

The origin of the central dogma through conflicting multilevel selection
438 downloads evolutionary biology

Nobuto Takeuchi, Kunihiko Kaneko

The central dogma of molecular biology rests on two kinds of asymmetry between genomes and enzymes: informatic asymmetry, where information flows from genomes to enzymes but not from enzymes to genomes; and catalytic asymmetry, where enzymes provide chemical catalysis but genomes do not. How did these asymmetries originate? Here we show that these asymmetries can spontaneously arise from conflict between selection at the molecular level and selection at the cellular level. We developed a model consisting of a population of protocells, each containing a population of replicating catalytic molecules. The molecules are assumed to face a trade-off between serving as catalysts and serving as templates. This trade-off causes conflicting multilevel selection: serving as catalysts is favoured by selection between protocells, whereas serving as templates is favoured by selection between molecules within protocells. This conflict induces informatic and catalytic symmetry breaking, whereby the molecules differentiate into genomes and enzymes, establishing the central dogma. We show mathematically that the symmetry breaking is caused by a positive feedback between Fisher's reproductive values and the relative impact of selection at different levels. This feedback induces a division of labour between genomes and enzymes, provided variation at the molecular level is sufficiently large relative to variation at the cellular level, a condition that is expected to hinder the evolution of altruism. Taken together, our results suggest that the central dogma is a logical consequence of conflicting multilevel selection.

8: Ancient Yersinia pestis genomes provide no evidence for the origins or spread of the Justinianic Plague
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Posted to bioRxiv 31 Oct 2019

Ancient Yersinia pestis genomes provide no evidence for the origins or spread of the Justinianic Plague
415 downloads evolutionary biology

Marcel Keller, Maria A. Spyrou, Michael McCormick, Kirsten I. Bos, Alexander Herbig, Johannes Krause

Along with the publication of 137 ancient human genomes retrieved from archaeological remains of the Eurasian steppe, [Damgaard et al., 2018][1] identified two individuals infected with Yersinia pestis , yielding one genome with 0.24x average coverage (DA147, 6th–9th c. AD) and another with 8.7x (DA101, 2nd–3rd c. AD). A phylogenetic analysis performed on the latter placed it in a position ancestral to a 6th-century Justinianic genome from Aschheim, Germany. These results are used to fuel an argument that the Justinianic Plague (541–544 AD) “was brought to Europe towards the end of the Hunnic period through the Silk Road along the southern fringes of the steppes” in contrast to the leading hypothesis of introduction via the Red Sea that is supported by historical accounts. In our reanalysis, we question the contested historical context of the presented genomes with the Justinianic Plague and show that the lower coverage genome might be rather related to the Black Death (1346–1353 AD). [1]: #ref-11

9: Genome Elimination Mediated by Gene Expression from a Selfish Chromosome
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Posted to bioRxiv 04 Oct 2019

Genome Elimination Mediated by Gene Expression from a Selfish Chromosome
392 downloads evolutionary biology

Elena Dalla Benetta, Igor Antoshechkin, Ting Yang, Hoa Quang My Nguyen, Patrick M. Ferree, Omar s Akbari

Numerous plants and animals harbor selfish B chromosomes that drive, or transmit themselves at higher-than-Mendelian frequencies, despite long-term fitness costs to the organism. Currently it is unknown how B chromosome drive is mediated, and whether B-gene expression plays a role. We used modern sequencing technologies to analyze the fine-scale sequence composition and expression of Paternal Sex Ratio (PSR), a B chromosome in the jewel wasp Nasonia vitripennis. PSR causes female-to-male conversion by destroying the sperms hereditary material in young embryos in order to drive. Using RNA interference, we show that testis-specific expression of a PSR-linked gene, named haploidizer, facilitates this genome elimination-and-sex conversion effect. Haploidizer shares homology with a gene in Candidatus cardinium, a bacterial symbiont that also induces genome elimination in its insect host.

10: Linking influenza virus evolution within and between human hosts
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Posted to bioRxiv 21 Oct 2019

Linking influenza virus evolution within and between human hosts
352 downloads evolutionary biology

Katherine S Xue, Jesse D Bloom

Influenza viruses rapidly diversify within individual human infections. Several recent studies have deep-sequenced clinical influenza infections to identify viral variation within hosts, but it remains unclear how within-host mutations fare in the global viral population. Here, we compare viral variation within and between hosts to link influenza's evolutionary dynamics across scales. Synonymous sites evolve at similar rates at both scales, indicating that global evolution at these putatively neutral sites results from the accumulation of within-host variation. However, nonsynonymous mutations are depleted in global viral populations compared to within hosts, suggesting that selection purges many of the protein-altering changes that arise within hosts. The exception is at antigenic sites, where selection detectably favors nonsynonymous mutations at the global scale, but not within hosts. These results suggest that selection against deleterious mutations and selection for antigenic change are the main forces that transform influenza's within-host genetic variation into global evolution.

11: Modelling the evolution of viral oncogenesis
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Posted to bioRxiv 18 Jan 2019

Modelling the evolution of viral oncogenesis
336 downloads evolutionary biology

Carmen Lía Murall, Samuel Alizon

Most human oncogenic viruses share several characteristics, such as being DNA viruses, having long (co)evolutionary histories with their hosts and causing either latent or chronic infections. They can reach high prevalences while causing relatively low case mortality, which makes them quite fit according to virulence evolution theory. After analysing the life-histories of DNA oncoviruses, we use a mathematical modelling approach to investigate how the virus life cycle may generate selective pressures favouring or acting against oncogenesis at the within-host or at the between-host level. In particular, we focus on two oncoprotein activities, namely extending cell life expectancy and increasing cell proliferation rate. These have immediate benefits (increasing viral population size) but can be associated with fitness costs at the epidemiological level (increasing recovery rate or risk of cancer) thus creating evolutionary trade-offs. We interpret the results of our nested model in the light of the biological features and identify future perspectives for modelling oncovirus dynamics and evolution.

12: Genetic signatures of evolutionary rescue by a selective sweep
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Posted to bioRxiv 10 Oct 2019

Genetic signatures of evolutionary rescue by a selective sweep
333 downloads evolutionary biology

Matthew Miles Osmond, Graham Coop

One of the most useful models in population genetics is that of a selective sweep and the consequent hitch-hiking of linked neutral alleles. While variations on this model typically assume constant population size, many instances of strong selection and rapid adaptation in nature may co-occur with complex demography. Here we extend the hitch-hiking model to evolutionary rescue, where adaptation and demography not only co-occur but are intimately entwined. Our results show how this feedback between demography and evolution determines the genetic signatures of evolutionary rescue, and how these differ from the signatures of sweeps in populations of constant size. In particular, we find rescue to harden sweeps from standing variance or new mutation (but not from migration), reduce nucleotide diversity both at the selected site and genome-wide, and increase the range of observed Tajima's $D$ values. For a given rate of population decline, the feedback between demography and evolution makes all of these differences more dramatic under weaker selection, where bottlenecks are prolonged. It is likely difficult to infer the co-incident timing of the sweep and bottleneck from these simple signatures, nevermind a feedback between them. However, temporal samples spanning contemporary rescue events may offer one way forward.

13: Large DNA virus promoted the endosymbiotic evolution to make a photosynthetic eukaryote
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Posted to bioRxiv 17 Oct 2019

Large DNA virus promoted the endosymbiotic evolution to make a photosynthetic eukaryote
318 downloads evolutionary biology

Mitsuhiro Matsuo, Atsushi Katahata, Makoto Tachikawa, Yohei Minakuchi, Hideki Noguchi, Atsushi Toyoda, Asao Fujiyama, Yutaka Suzuki, Takayuki Hata, Soichirou Satoh, Takuro Nakayama, Ryoma Kamikawa, Mami Nomura, Yuji Inagaki, Ken-ichiro Ishida, Junichi Obokata

Chloroplasts in photosynthetic eukaryotes originated from a cyanobacterial endosymbiosis far more than 1 billion years ago[1][1]-[3][2]. Due to this ancientness, it remains unclear how this evolutionary process proceeded. To unveil this mystery, we analysed the whole genome sequence of a photosynthetic rhizarian amoeba[4][3], Paulinella micropora [5][4],[6][5], which has a chloroplast-like organelle that originated from another cyanobacterial endosymbiosis[7][6]-[10][7] about 0.1 billion years ago[11][8]. Here we show that the predacious amoeba that engulfed cyanobacteria evolved into a photosynthetic organism very quickly in the evolutionary time scale, probably aided by the drastic genome reorganization activated by large DNA virus. In the endosymbiotic evolution of eukaryotic cells, gene transfer from the endosymbiont genome to the host nucleus is essential for the evolving host cell to control the endosymbiont-derived organelle[12][9]. In P. micropora , we found that the gene transfer from the free-living and endosymbiotic bacteria to the amoeba nucleus was rapidly activated but both simultaneously ceased within the initiation period of the endosymbiotic evolution, suggesting that the genome reorganization drastically proceeded and completed. During this period, large DNA virus appeared to have infected the amoeba, followed by the rapid amplification and diversification of virus-related genes. These findings led us to re-examine the conventional endosymbiotic evolutionary scenario that exclusively deals with the host and the symbiont, and to extend it by incorporating a third critical player, large DNA virus, which activates the drastic gene transfer and genome reorganization between them. This Paulinella version of the evolutionary hypothesis deserves further testing of its generality in evolutionary systems and could shed light on the unknown roles of large DNA viruses[13][10] in the evolution of terrestrial life. [1]: #ref-1 [2]: #ref-3 [3]: #ref-4 [4]: #ref-5 [5]: #ref-6 [6]: #ref-7 [7]: #ref-10 [8]: #ref-11 [9]: #ref-12 [10]: #ref-13

14: Disentangling Sources of Gene Tree Discordance in Phylotranscriptomic Datasets: A Case Study from Amaranthaceae s.l.
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Posted to bioRxiv 07 Oct 2019

Disentangling Sources of Gene Tree Discordance in Phylotranscriptomic Datasets: A Case Study from Amaranthaceae s.l.
310 downloads evolutionary biology

Diego F Morales-Briones, Gudrun Kadereit, Delphine T Tefarikis, Michael Moore, Stephen A. Smith, Samuel F. Brockington, Alfonso Timoneda, Won C Yim, John C Cushman, Ya Yang

Phylogenomic datasets have become common and fundamental to understanding the phylogenetic relationships of recalcitrant groups across the Tree of Life. At the same time, working with large genomic or transcriptomic datasets requires special attention to the processes that generate gene tree discordance, such as data processing and orthology inference, incomplete lineage sorting, hybridization, model violation, and uninformative gene trees. Methods to estimate species trees from phylogenomic datasets while accounting for all sources of conflict are not available, but a combination of multiple approaches can be a powerful tool to tease apart alternative sources of conflict. Here using a phylotranscriptomic analysis in combination with reference genomes, we explore sources of gene tree discordance in the backbone phylogeny of the plant family Amaranthaceae s.l. The dataset was analyzed using multiple phylogenetic approaches, including coalescent-based species trees and network inference, gene tree discordance analyses, site pattern test of introgression, topology test, synteny analyses, and simulations. We found that a combination of processes might have acted, simultaneously and/or cumulatively, to generate the high levels of gene tree discordance in the backbone of Amaranthaceae s.l. Furthermore, other analytical shortcomings like uninformative genes as well as misspecification of the model of molecular evolution seem to contribute to tree discordance signal in this family. Despite the comprehensive phylogenomic dataset and detailed analyses presented here, no single source can confidently be pointed out to account for the strong signal of gene tree discordance, suggesting that the backbone of Amaranthaceae s.l. might be a product of an ancient and rapid lineage diversification, and remains -and probably will remain- unresolved even with genome-scale data. Our work highlights the need to test for multiple sources of conflict in phylogenomic analyses and provide a set of recommendations moving forward in disentangling ancient and rapid diversification.

15: The Impact of Cross-Species Gene Flow on Species Tree Estimation
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Posted to bioRxiv 25 Oct 2019

The Impact of Cross-Species Gene Flow on Species Tree Estimation
295 downloads evolutionary biology

Xiyun Jiao, Thomas Flouris, Bruce Rannala, Ziheng Yang

Recent analyses of genomic sequence data suggest cross-species gene flow is common in both plants and animals, posing challenges to species tree inference. We examine the levels of gene flow needed to mislead species tree estimation with three species and either episodic introgressive hybridization or continuous migration between an outgroup and one ingroup species. Several species tree estimation methods are examined, including the majority-vote method based on the most common gene tree topology (with either the true or reconstructed gene trees used), the UPGMA method based on the average sequence distances (or average coalescent times) between species, and the full-likelihood method based on multi-locus sequence data. Our results suggest that the majority-vote method is more robust to gene flow than the UPGMA method and both are more robust than likelihood assuming a multispecies coalescent (MSC) model with no cross-species gene flow. A small amount of introgression or migration can mislead species tree methods if the species diverged through speciation events separated by short time intervals.Estimates of parameters under the MSC with gene flow suggest the Anopheles gambia African mosquito species complex is an example where gene flow greatly impacts species phylogeny.

16: Population Replacement in Early Neolithic Britain
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Posted to bioRxiv 18 Feb 2018

Population Replacement in Early Neolithic Britain
278 downloads evolutionary biology

Selina Brace, Yoan Diekmann, Thomas J. Booth, Zuzana Faltyskova, Nadin Rohland, Swapan Mallick, Matthew Ferry, Megan Michel, Jonas Oppenheimer, Nasreen Broomandkhoshbacht, Kristin Stewardson, Susan Walsh, Manfred Kayser, Rick Schulting, Oliver E Craig, Alison Sheridan, Mike Parker Pearson, Chris Stringer, David Reich, Mark G. Thomas, Ian Barnes

The roles of migration, admixture and acculturation in the European transition to farming have been debated for over 100 years. Genome-wide ancient DNA studies indicate predominantly Anatolian ancestry for continental Neolithic farmers, but also variable admixture with local Mesolithic hunter-gatherers. Neolithic cultures first appear in Britain c. 6000 years ago (kBP), a millennium after they appear in adjacent areas of northwestern continental Europe. However, the pattern and process of the British Neolithic transition remains unclear. We assembled genome-wide data from six Mesolithic and 67 Neolithic individuals found in Britain, dating from 10.5-4.5 kBP, a dataset that includes 22 newly reported individuals and the first genomic data from British Mesolithic hunter-gatherers. Our analyses reveals persistent genetic affinities between Mesolithic British and Western European hunter-gatherers over a period spanning Britain's separation from continental Europe. We find overwhelming support for agriculture being introduced by incoming continental farmers, with small and geographically structured levels of additional hunter-gatherer introgression. We find genetic affinity between British and Iberian Neolithic populations indicating that British Neolithic people derived much of their ancestry from Anatolian farmers who originally followed the Mediterranean route of dispersal and likely entered Britain from northwestern mainland Europe.

17: Evolution of microbial growth traits under serial dilution
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Posted to bioRxiv 09 Oct 2019

Evolution of microbial growth traits under serial dilution
274 downloads evolutionary biology

Jie Lin, Michael Manhart, Ariel Amir

Selection of mutants in a microbial population depends on multiple cellular traits. In serial-dilution evolution experiments, three key traits are the lag time when transitioning from starvation to growth, the exponential growth rate, and the yield (number of cells per unit resource). Here we investigate how these traits evolve in laboratory evolution experiments using a minimal model of population dynamics, where the only interaction between cells is competition for a single limiting resource. We find that the fixation probability of a beneficial mutation depends on a linear combination of its growth rate and lag time relative to its immediate ancestor, even under clonal interference. The relative selective pressure on growth rate and lag time is set by the dilution factor; a larger dilution factor favors the adaptation of growth rate over the adaptation of lag time. The model shows that yield, however, is under no direct selection. We also show how the adaptation speeds of growth and lag depend on experimental parameters and the underlying supply of mutations. Finally, we investigate the evolution of covariation between these traits across populations, which reveals that the population growth rate and lag time can evolve a nonzero correlation even if mutations have uncorrelated effects on the two traits. Altogether these results provide useful guidance to future experiments on microbial evolution.

18: Prototypic SNARE proteins are encoded in the genomes of Heimdallarchaeota, potentially bridging the gap between the prokaryotes and eukaryotes
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Posted to bioRxiv 18 Oct 2019

Prototypic SNARE proteins are encoded in the genomes of Heimdallarchaeota, potentially bridging the gap between the prokaryotes and eukaryotes
269 downloads evolutionary biology

Emilie Neveu, Dany Khalifeh, Nicolas Salamin, Dirk Fasshauer

A defining feature of eukaryotic cells is the presence of numerous membrane-bound organelles that subdivide the intracellular space into distinct compartments. How the eukaryotic cell acquired its internal complexity is still poorly understood. Material exchange among most organelles occurs via vesicles that bud off from a source and specifically fuse with a target compartment. Central players in the vesicle fusion process are the Soluble N -ethylmaleimide-sensitive factor Attachment protein REceptor (SNARE) proteins. These small tail-anchored (TA) membrane proteins zipper into elongated four-helix bundles that pull membranes together[1][1]–[3][2]. SNARE proteins are highly conserved among eukaryotes but are thought to be absent in prokaryotes. Here, we identified SNARE-like factors in the genomes of uncultured organisms of Asgard archaea of the Heimdallarchaeota clade[4][3],[5][4], which are thought to be the closest living relatives of eukaryotes. Biochemical experiments show that the archaeal SNARE-like proteins can interact with eukaryotic SNARE proteins. We did not detect SNAREs in α-proteobacteria, the closest relatives of mitochondria, but identified several genes encoding for SNARE proteins in γ-proteobacteria of the order Legionellales, pathogens that live inside eukaryotic cells. Very probably, their SNAREs stem from lateral gene transfer from eukaryotes. Together, this suggests that the diverse set of eukaryotic SNAREs evolved from an archaeal precursor. However, whether Heimdallarchaeota actually have a simplified endomembrane system will only be seen when we succeed studying these organisms under the microscope. * SNARE : Soluble N -ethylmaleimide-sensitive factor attachment protein receptor TMD : transmembrane domain MCP : methyl-accepting chemotaxis protein HMM : Hidden Markov Model TA : tail anchored GET : Guided Entry of Tail-anchored proteins HPS : Heimdallarchaeota Prototypic SNARE AU : Approximately Unbiased [1]: #ref-1 [2]: #ref-3 [3]: #ref-4 [4]: #ref-5

19: Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals
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Posted to bioRxiv 25 Oct 2019

Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals
267 downloads evolutionary biology

Denis V. Tikhonenkov, Elisabeth Hehenberger, Anton S. Esaulov, Olga I. Belyakova, Yuri A. Mazei, Alexander P. Mylnikov, Patrick J Keeling

The diversity and biology of unicellular relatives of animals has strongly informed our understanding of the transition from single-celled organisms to the multicellular Metazoa. Here we analyse the cellular structures and complex life cycles of the novel unicellular holozoans Pigoraptor and Syssomonas (Opisthokonta). Both lineages are characterized by complex life cycles with a variety of cell types, the formation of multicellular aggregations and syncytium-like structures, and an unusual diet for single-celled opisthokonts (partial cell fusion and joint sucking of a large eukaryotic prey), all of which provide new insights into the origin of multicellularity in Metazoa. The ability to feed on large eukaryotic prey could have been a powerful trigger in the formation and development both aggregative (e.g., joint feeding, which also implies signalling) and clonal (e.g., hypertrophic growth followed by palintomy) multicellular stages that played important roles in the emergence of multicellular animals.

20: Eco-evolutionary dynamics of nested Darwinian populations and the emergence of community-level heredity
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Posted to bioRxiv 04 Nov 2019

Eco-evolutionary dynamics of nested Darwinian populations and the emergence of community-level heredity
266 downloads evolutionary biology

Guilhem Doulcier, Amaury Lambert, Silvia De Monte, Paul Rainey

Interactions among microbial cells can generate new chemistries and functions, but exploitation requires establishment of communities that reliably recapitulate community-level phenotypes. Using mechanistic mathematical models, we show how simple manipulations to population structure can exogenously impose Darwinian-like properties on communities. Such imposition causes communities to participate directly in the process of evolution by natural selection and drives the evolution of cell-level interactions to the point where, despite underlying stochasticity, derived communities give rise to offspring communities that faithfully re-establish parental phenotype. The mechanism (developmental correction) is akin to a developmental process that arises from density dependent interactions among cells. Knowledge of ecological factors affecting evolution of developmental correction has implications for understanding the evolutionary origin of egalitarian transitions in individuality, symbioses, and for top-down engineering of microbial communities.

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