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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 62,933 bioRxiv papers from 279,142 authors.

Most downloaded bioRxiv papers, since beginning of last month

in category evolutionary biology

4,145 results found. For more information, click each entry to expand.

1: Single-cell-resolution transcriptome map of human, chimpanzee, bonobo, and macaque brains
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Posted to bioRxiv 10 Sep 2019

Single-cell-resolution transcriptome map of human, chimpanzee, bonobo, and macaque brains
1,077 downloads evolutionary biology

Ekaterina Khrameeva, Ilia Kurochkin, Dingding Han, Patricia Guijarro, Sabina Kanton, Malgorzata Santel, Zhengzong Qian, Shen Rong, Pavel Mazin, Matvei Bulat, Olga Efimova, Anna Tkachev, Song Guo, Chet Sherwood, Gray Camp, Svante Paabo, Barbara Treutlein, Philipp Khaitovich

Identification of gene expression traits unique to the human brain sheds light on the mechanisms of human cognition. Here we searched for gene expression traits separating humans from other primates by analyzing 88,047 cell nuclei and 422 tissue samples representing 33 brain regions of humans, chimpanzees, bonobos, and macaques. We show that gene expression evolves rapidly within cell types, with more than two-thirds of cell type-specific differences not detected using conventional RNA sequencing of tissue samples. Neurons tend to evolve faster in all hominids, but non-neuronal cell types, such as astrocytes and oligodendrocyte progenitors, show more differences on the human lineage, including alterations of spatial distribution across neocortical layers.

2: Most cancers carry a substantial deleterious load due to Hill-Robertson interference
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Posted to bioRxiv 14 Sep 2019

Most cancers carry a substantial deleterious load due to Hill-Robertson interference
815 downloads evolutionary biology

Susanne Tilk, Christina Curtis, Dmitri Petrov, Christopher Dennis McFarland

Introduction Cancer genomes exhibit surprisingly weak signatures of negative selection[1][1],[2][2]. This may be because tumors evolve either under very weak selective pressures (‘weak selection’) or under conditions that prevent the elimination of many deleterious passenger mutations (‘poor efficacy of selection’)xs. Rationale The weak selection model argues that the majority of genes are only important for multicellular function. The poor efficacy of selection model argues, in contrast, that genome-wide linkage in cancer prevents many deleterious mutations from being removed via Hill-Robertson interference[3][3]. Since these linkage effects weaken as mutation rates decrease, we predict that cancers with lower mutational burdens should exhibit stronger signals of negative selection. Furthermore, because linkage affects driver mutations as well, low mutational burden cancers should also show stronger evidence of positive selection in driver genes. Neither pattern — in drivers or passengers — is expected under the weak selection model. We leverage the 10,000-fold variation in mutational burden across cancer subtypes to stratify tumors by their genome-wide mutational burden and used a normalized ratio of nonsynonymous to synonymous substitutions (dN/dS) to quantify the extent that selection varies with mutation rate. Results We find that appreciable negative selection (dN/dS ~ 0.4) is present in tumors with a low mutational burden, while the remaining cancers (96%) exhibit dN/dS ratios approaching 1, suggesting that the majority of tumors do not remove deleterious passengers. A parallel pattern is seen in drivers, where positive selection attenuates as the mutational burden of cancers increases. Both trends persist across tumor-types, are not exclusive to essential or housekeeping genes, and are present in clonal and subclonal mutations. Two additional orthogonal lines of evidence support the weak efficacy model: passengers are less damaging in low mutational burden cancers, and patterns of attenuated selection also emerge in Copy Number Alterations. Finally, we find that an evolutionary model incorporating Hill-Robertson interference can reproduce both patterns of attenuated selection in drivers and passengers if the average fitness cost of passengers is 1.0% and the average fitness benefit of drivers is 19%. Conclusion Collectively, our findings suggest that the lack of signals of negative selection in most tumors is not due to relaxed selective pressures, but rather the inability of selection to remove individual deleterious mutations in the presence of genome-wide linkage. As a result, despite the weak individual fitness effects of passengers, most cancers harbor a large mutational load (median ~40% total fitness cost) and succeed due to acquisition of additional strong drivers (~5 with an overall benefit of ~130%). Understanding how this deleterious load is overcome may help identify cancer vulnerabilities that may be targeted by new and existing therapies. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3

3: 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
528 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.

4: Deviations from Hardy Weinberg Equilibrium at CCR5-Δ32 in Large Sequencing Data Sets?
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Posted to bioRxiv 14 Sep 2019

Deviations from Hardy Weinberg Equilibrium at CCR5-Δ32 in Large Sequencing Data Sets?
513 downloads evolutionary biology

Xinzhu Wei, Rasmus Nielsen

We have been made aware by Mark Daly and colleagues that there might be genotyping errors in the gnomeAD database. Also, David Reich and colleagues have pointed out a genotyping error in the UK Biobank that might also affect our results of this paper and certainly has affected our previous paper. For this reason, some of the results in the posted version of this paper may no longer hold up and we ask other researchers to disregard the evidence in this paper pending further inquiry.

5: Genome Tree of Life: Deep Burst of Organism Diversity
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Posted to bioRxiv 05 Sep 2019

Genome Tree of Life: Deep Burst of Organism Diversity
484 downloads evolutionary biology

JaeJin Choi, Sung-Hou Kim

An organism Tree of Life (organism ToL) is a conceptual and metaphorical tree to capture a simplified narrative of the evolutionary course and kinship among the extant organisms of today. Such tree cannot be experimentally validated, but may be reconstructed based on characteristics associated with the organisms. Since the whole genome sequence of an organism is, at present, the most comprehensive descriptor of the organism, a genome Tol can be an empirically derivable surrogate for the organism ToL. However, a genome ToL has been impossible to construct because of the practical reasons that experimentally determining the whole genome sequences of a large number of diverse organisms was technically impossible. Thus, for several decades gene ToLs based on selected genes have been commonly used as a surrogate for the organisms ToL. This situation changed dramatically during the last several decades due to rapid advances in DNA sequencing technology. Here we present a genome ToL, which shows that (a) whole genome information can be compared without sequence alignment, (b) all extant organisms can be classified into six large groups and (c) all the founders of the groups have emerged in a Deep Burst at the very beginning period of the emergence of the Life on Earth.

6: 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
397 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.

7: Complex eukaryotic-like actin regulation systems from Asgard archaea
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Posted to bioRxiv 14 Sep 2019

Complex eukaryotic-like actin regulation systems from Asgard archaea
361 downloads evolutionary biology

Caner Akil, Linh T Tran, Magali Orhant-Prioux, Yohendran Baskaran, Edward Manser, Laurent Blanchoin, Robert C Robinson

Asgard archaea genomes contain potential eukaryotic-like genes that provide intriguing insight for the evolution of eukaryotes. The actin polymerization/depolymerization cycle is critical for providing force and structure for a variety of processes in eukaryotes, including membrane remodelling. Here, we identify actin filament severing, capping, annealing and bundling, and monomer sequestration activities by gelsolin proteins from Thorarchaeota (Thor), which complete a eukaryote-like actin depolymerization cycle. Thor gelsolins are comprised of one or two copies of the prototypical gelsolin domain and appear to be a record of an initial pre-eukaryotic gene duplication event, since eukaryotic gelsolins are generally comprised of three to six domains. X-ray crystal structure determination of these proteins in complex with mammalian actin revealed similar interactions to the first domain of human gelsolin. Asgard two-domain, but not one-domain, gelsolins contain calcium-binding sites, which is manifested in calcium-controlled activities. Expression of two-domain gelsolins in mammalian cells led to enhanced actin filament disassembly on ionomycin-triggered calcium release. This functional demonstration, at the cellular level, provides evidence for calcium-regulated actin cytoskeleton in Asgard archaea, and indicates that the calcium-regulated actin cytoskeleton predates eukaryotes. In eukaryotes, dynamic bundled filaments are responsible for shaping filopodia and microvilli. By correlation, the formation of the protrusions observed from Lokiarchaeota cell bodies may involve gelsolin-regulated actin structures.

8: The evolutionary plasticity of chromosome metabolism allows adaptation to DNA replication stress
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Posted to bioRxiv 16 Sep 2019

The evolutionary plasticity of chromosome metabolism allows adaptation to DNA replication stress
349 downloads evolutionary biology

Marco Fumasoni, Andrew W. Murray

Chromosome metabolism is defined by the pathways that collectively maintain the genome, including chromosome replication, repair and segregation. Because aspects of these pathways are conserved, chromosome metabolism is considered resistant to evolutionary change. We used the budding yeast, Saccharomyces cerevisiae , to investigate the evolutionary plasticity of chromosome metabolism. We experimentally evolved cells constitutively experiencing DNA replication stress caused by the absence of Ctf4, a protein that coordinates the activities at replication forks. Parallel populations adapted to replication stress, over 1000 generations, by acquiring multiple, successive mutations. Whole-genome sequencing and testing candidate mutations revealed adaptive changes in three aspects of chromosome metabolism: DNA replication, DNA damage checkpoint and sister chromatid cohesion. Although no gene was mutated in every population, the same pathways were sequentially altered, defining a functionally reproducible evolutionary trajectory. We propose that this evolutionary plasticity of chromosome metabolism has important implications for genome evolution in natural populations and cancer.

9: Genomic history and ecology of the geographic spread of rice
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Posted to bioRxiv 31 Aug 2019

Genomic history and ecology of the geographic spread of rice
343 downloads evolutionary biology

Rafal M Gutaker, Simon Groen, Emily Sarah Bellis, Jae Young Choi, Inês S Pires, R Kyle Bocinsky, Emma R Slayton, Olivia Wilkins, Cristina C Castillo, Sonia Negrão, M. Margarida Oliveira, Dorian Q Fuller, Jade A d'Alpoim Guedes, Jesse R Lasky, Michael D. Purugganan

Rice (Oryza sativa) is one of the world's most important food crops. We reconstruct the history of rice dispersal in Asia using whole-genome sequences of >1,400 landraces, coupled with geographic, environmental, archaeobotanical and paleoclimate data. We also identify extrinsic factors that impact genome diversity, with temperature a leading abiotic factor. Originating ~9,000 years ago in the Yangtze Valley, rice diversified into temperate and tropical japonica during a global cooling event ~4,200 years ago. Soon after, tropical rice reached Southeast Asia, where it rapidly diversified starting ~2,500 yBP. The history of indica rice dispersal appears more complicated, moving into China ~2,000 yBP. Reconstructing the dispersal history of rice and its climatic correlates may help identify genetic adaptation associated with the spread of a key domesticated species.

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

Massive haplotypes underlie ecotypic differentiation in sunflowers
331 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.

11: Haplotype-based inference of the distribution of fitness effects
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Posted to bioRxiv 16 Sep 2019

Haplotype-based inference of the distribution of fitness effects
317 downloads evolutionary biology

Diego Ortega-Del Vecchyo, Kirk E Lohmueller, John Novembre

Recent genome sequencing studies with large sample sizes in humans have discovered a vast quantity of low-frequency variants, providing an important source of information to analyze how selection is acting on human genetic variation. In order to estimate the strength of natural selection acting on low-frequency variants, we have developed a likelihood-based method that uses the lengths of pairwise identity-by-state between haplotypes carrying low-frequency variants. We show that in some non-equilibrium populations (such as those that have had recent population expansions) it is possible to distinguish between positive or negative selection acting on a set of variants. With our new framework, one can infer a fixed selection intensity acting on a set of variants at a particular frequency, or a distribution of selection coefficients for standing variants and new mutations. We apply our method to the UK10K phased haplotype dataset of 3,781 individuals and find a similar proportion of neutral, moderately deleterious, and deleterious variants compared to previous estimates made using the site frequency spectrum. We discuss several interpretations for this result, including that selective constraints have remained constant over time.

12: Phylogenies of extant species are consistent with an infinite array of diversification histories
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Posted to bioRxiv 31 Jul 2019

Phylogenies of extant species are consistent with an infinite array of diversification histories
300 downloads evolutionary biology

Stilianos Louca, Matthew W Pennell

Time-calibrated molecular phylogenies of extant species ("extant timetrees") are widely used for estimating the dynamics of diversification rates ([1][1]–[6][2]) and testing for associations between these rates and environmental factors ([5][3], [7][4]) or species traits ([8][5]). However, there has been considerable debate surrounding the reliability of these inferences in the absence of fossil data ([9][6]–[13][7]), and to date this critical question remains unresolved. Here we mathematically clarify the precise information that can be extracted from extant timetrees under the generalized birth-death model, which underlies the majority of existing estimation methods. We prove that for a given extant timetree and a candidate diversification scenario, there exists an infinite number of alternative diversification scenarios that are equally likely to have generated a given tree. These “congruent” scenarios cannot possibly be distinguished using extant timetrees alone, even in the presence of infinite data. Importantly, congruent diversification scenarios can exhibit markedly different and yet plausible diversification dynamics, suggesting that many previous studies may have over-interpreted phylogenetic evidence. We show that sets of congruent models can be uniquely described using composite variables, which contain all available information about past dynamics of diversification ([14][8]); this suggests an alternative paradigm for learning about the past from extant timetrees. [1]: #ref-1 [2]: #ref-6 [3]: #ref-5 [4]: #ref-7 [5]: #ref-8 [6]: #ref-9 [7]: #ref-13 [8]: #ref-14

13: Bacterial genes outnumber archaeal genes in eukaryotic genomes
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Posted to bioRxiv 23 Sep 2019

Bacterial genes outnumber archaeal genes in eukaryotic genomes
298 downloads evolutionary biology

Julia Brückner, William F. Martin

The origin of eukaryotes is one of evolution’s most important transitions, yet it is still poorly understood. Evidence for how it occurred should be preserved in eukaryotic genomes. Based on phylogenetic trees from ribosomal RNA and ribosomal proteins, eukaryotes are typically depicted as branching together with or within archaea. This ribosomal affiliation is widely interpreted as evidence for an archaeal origin of eukaryotes. However, the extent to which the archaeal ancestry of genes for the cytosolic ribosomes of eukaryotic cells is representative for the rest of the eukaryotic genome is unknown. Here we have clustered 19,050,992 protein sequences from 5,443 bacteria and 212 archaea with 3,420,731 protein sequences from 150 eukaryotes spanning six eukaryotic supergroups to identify genes that link eukaryotes exclusively to bacteria and archaea respectively. By downsampling the bacterial sample we obtain estimates for the bacterial and archaeal proportions of genes among 150 eukaryotic genomes. Eukaryotic genomes possess a bacterial majority of genes. On average, eukaryotic genes are 56% bacterial in origin. The majority drops to 53% in eukaryotes that never possessed plastids, and increases to 61% in photosynthetic eukaryotic lineages, where the cyanobacterial ancestor of plastids contributed additional genes to the eukaryotic genome, reaching 67% in higher plants. Intracellular parasites, which undergo reductive evolution in adaptation to the nutrient rich environment of the cells that they infect, relinquish bacterial genes for metabolic processes. In the current sample, this process of adaptive gene loss is most pronounced in the human parasite Encephalitozoon intestinalis with 86% archaeal and 14% bacterial derived genes. The most bacterial eukaryote genome sampled is rice, with 67% bacterial and 33% archaeal genes. The functional dichotomy, initially described for yeast, of archaeal genes being involved in genetic information processing and bacterial genes being involved in metabolic processes is conserved across all eukaryotic supergroups.

14: On the relative ease of speciation with periodic gene flow
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Posted to bioRxiv 08 Sep 2019

On the relative ease of speciation with periodic gene flow
295 downloads evolutionary biology

Ethan B. Linck, C. J. Battey

Common models of speciation with gene flow consider constant migration or admixture on secondary contact, but earth’s recent climatic history suggests many populations have experienced cycles of isolation and contact over the last million years. How does this process impact the rate of speciation, and how much can we learn about its dynamics by analyzing the genomes of modern populations? Here we develop a simple model of speciation through Bateson-Dobzhansky-Muller incompatibilities in the face of periodic gene flow and validate our model with forward time simulations. We then use empirical atmospheric CO 2 concentration data from the Vostok Ice Cores to simulate cycles of isolation and secondary contact in a tropical montane landscape, and ask whether they can be distinguished from a standard isolation-with-migration model by summary statistics or joint site frequency spectrum-based demographic inference. We find speciation occurs much faster under periodic than constant gene flow with equivalent effective migration rates ( Nm ). These processes can be distinguished through combinations of summary statistics or demographic inference from the site frequency spectrum, but parameter estimates appear to have little resolution beyond the most recent cycle of isolation and migration. Our results suggest speciation with periodic gene flow is a common force in generating species diversity through Pleistocene climate cycles, and highlight the limits of current inference techniques for demographic models mimicking the complexity of earth’s recent climatic history.

15: Evolution of herbivory remodels a Drosophila genome
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Posted to bioRxiv 12 Sep 2019

Evolution of herbivory remodels a Drosophila genome
294 downloads evolutionary biology

Andrew D Gloss, Anna C Nelson Dittrich, Richard T Lapoint, Benjamin Goldman Huertas, Kirsten I. Verster, Julianne L Pelaez, Andrew D.L. Nelson, Jessica Aguilar, Ellie Armstrong, Joseph L.M. Charboneau, Simon C Groen, David H Hembry, Christopher J Ochoa, Timothy K O'Connor, Stefan Prost, Hiromu C Suzuki, Sophie Zaaijer, Paul D Nabity, Noah K Whiteman

One-quarter of extant Eukaryotic species are herbivorous insects, yet the genomic basis of this extraordinary adaptive radiation is unclear. Recently-derived herbivorous species hold promise for understanding how colonization of living plant tissues shaped the evolution of herbivore genomes. Here, we characterized exceptional patterns of evolution coupled with a recent (<15 mya) transition to herbivory of mustard plants (Brassicaceae, including Arabidopsis thaliana) in the fly genus Scaptomyza, nested within the paraphyletic genus Drosophila. We discovered a radiation of mustard-specialized Scaptomyza species, comparable in diversity to the Drosophila melanogaster species subgroup. Stable isotope, behavioral, and viability assays revealed these flies are obligate herbivores. Genome sequencing of one species, S. flava, revealed that the evolution of herbivory drove a contraction in gene families involved in chemosensation and xenobiotic metabolism. Against this backdrop of losses, highly targeted gains ("blooms") were found in Phase I and Phase II detoxification gene sub-families, including glutathione S-transferase (Gst) and cytochrome P450 (Cyp450) genes. S. flava has more validated paralogs of a single Cyp450 (N=6 for Cyp6g1) and Gst (N=5 for GstE5-8) than any other drosophilid. Functional studies of the Gst repertoire in S. flava showed that transcription of S. flava GstE5-8 paralogs was differentially regulated by dietary mustard oils, and of 22 heterologously expressed cytosolic S. flava GST enzymes, GSTE5-8 enzymes were exceptionally well-adapted to mustard oil detoxification in vitro. One, GSTE5-8a, was an order of magnitude more efficient at metabolizing mustard oils than GSTs from any other metazoan. The serendipitous intersection of two genetic model organisms, Drosophila and Arabidopsis, helped illuminate how an insect genome was remodeled during the evolutionary transformation to herbivory, identifying mechanisms that facilitated the evolution of the most diverse guild of animal life.

16: Ancient genomic regulatory blocks are a major source for gene deserts in vertebrates after whole genome duplications
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Posted to bioRxiv 25 Sep 2019

Ancient genomic regulatory blocks are a major source for gene deserts in vertebrates after whole genome duplications
290 downloads evolutionary biology

Maria Touceda-Suarez, Elisabeth M. Kita, Rafael D Acemel, Panos N. Firbas, Marta S. Magri, Silvia Naranjo, Juan J. Tena, Jose Luis Gomez-Skarmeta, Ignacio Maeso, Manuel Irimia

We investigated how the two rounds of whole genome duplication that occurred at the base of the vertebrate lineage have impacted ancient microsyntenic associations involving developmental regulators (known as genomic regulatory blocks, GRBs). We showed that the majority of GRBs present in the last common ancestor of chordates have been maintained as a single copy in humans. We found evidence that dismantling of the additional GRB copies occurred early in vertebrate evolution often through the differential retention of the regulatory gene but loss of the bystander gene's exonic sequences. Despite the large evolutionary scale, the presence of duplicated highly conserved non-coding regions provided unambiguous proof for this scenario for dozens of ancient GRBs. Remarkably, the dismantling of ancient GRB duplicates has contributed to the creation of large gene deserts associated with regulatory genes in vertebrates, providing a widespread mechanism for the origin of these enigmatic genomic traits.

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

Modelling the evolution of viral oncogenesis
276 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.

18: A Bayesian implementation of the multispecies coalescent model with introgression for comparative genomic analysis
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Posted to bioRxiv 14 Sep 2019

A Bayesian implementation of the multispecies coalescent model with introgression for comparative genomic analysis
256 downloads evolutionary biology

Thomas Flouris, Xiyun Jiao, Bruce Rannala, Ziheng Yang

Recent analyses suggest that cross-species gene flow or introgression is common in nature, especially during species divergences. Genomic sequence data can be used to infer introgression events and to estimate the timing and intensity of introgression, providing an important means to advance our understanding of the role of gene flow in speciation. Here we implement the multispecies-coalescent-with-introgression (MSci) model, an extension of the multispecies-coalescent (MSC) model to incorporate introgression, in our Bayesian Markov chain Monte Carlo (MCMC) program BPP. The MSci model accommodates deep coalescence (or incomplete lineage sorting) and introgression and provides a natural framework for inference using genomic sequence data. Computer simulation confirms the good statistical properties of the method, although hundreds or thousands of loci are typically needed to estimate introgression probabilities reliably. Re-analysis of datasets from the purple cone spruce confirms the hypothesis of homoploid hybrid speciation. We estimated the introgression probability using the genomic sequence data from six mosquito species in the Anopheles gambiae species complex, which varies considerably across the genome, likely driven by differential selection against introgressed alleles.

19: Integrated evolutionary and structural analysis reveals xenobiotics and pathogens as the major drivers of mammalian adaptation
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Posted to bioRxiv 09 Sep 2019

Integrated evolutionary and structural analysis reveals xenobiotics and pathogens as the major drivers of mammalian adaptation
253 downloads evolutionary biology

Greg Slodkowicz, Nick Goldman

Understanding the molecular basis of adaptation to the environment is a central question in evolutionary biology, yet linking detected signatures of positive selection to molecular mechanisms remains challenging. Here we demonstrate that combining sequence-based phylogenetic methods with structural information assists in making such mechanistic interpretations on a genomic scale. Our integrative analysis shows that positively selected sites tend to co-localise on protein structures and that positively selected clusters are found in functionally important regions of proteins, indicating that positive selection can contravene the well-known principle of evolutionary conservation of functionally important regions. This unexpected finding, along with our discovery that positive selection acts on structural clusters, opens new strategies for the development of better models of protein evolution. Remarkably, proteins where we detect the strongest evidence of clustering belong to just two functional groups: components of immune response and metabolic enzymes. This gives a coherent picture of immune response and xenobiotic metabolism as the drivers of adaptive evolution of mammals.

20: Common genetic variants shape broad patterns of within-population variation in gene expression.
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Posted to bioRxiv 10 Sep 2019

Common genetic variants shape broad patterns of within-population variation in gene expression.
252 downloads evolutionary biology

Emily B. Josephs, Young Wha Lee, Corlett Wolfe Wood, Daniel Schoen, Stephen Wright, John Stinchcombe

Understanding the persistence of genetic variation within populations has long been a goal of evolutionary biology. One promising route towards achieving this goal is using population genetic approaches to describe how selection acts on the loci associated with trait variation. In particular, gene expression provides a model trait for addressing the challenge of the maintenance of variation because it can be measured genome-wide without information about how gene expression affects traits. Previous work has shown that loci affecting the expression of nearby genes (cis-eQTL) tend to be under purifying selection, but we lack a clear understanding of the selective forces acting on variants that affect the expression of large numbers of genes across the genome (large-effect trans-eQTL). Here, we identify loci that affect the expression of coexpression networks using genomic and transcriptomic data from one population of the obligately outcrossing plant, Capsella grandiflora. We identify nine loci associated with the expression of 10s to 1000s of genes. One of these loci is also associated with trait variation, but we do not detect evidence of balancing selection acting on sequence variation surrounding these loci.

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