scholarly journals Natural selection and recombination rate variation shape nucleotide polymorphism across the genomes of three relatedPopulusspecies

2015 ◽  
Author(s):  
Jing Wang ◽  
Nathaniel R Street ◽  
Douglas G Scofield ◽  
Pär K Ingvarsson
Keyword(s):  
Natural Selection ◽  
Rate Variation ◽  
Sequencing Data ◽  
Nucleotide Polymorphism ◽  
Effective Population ◽  
Recombination Rates ◽  
Evolutionary Forces ◽  
Genome Wide ◽  
Population Sizes ◽  
Wide Scale

AbstractA central aim of evolutionary genomics is to identify the relative roles that various evolutionary forces have played in generating and shaping genetic variation within and among species. Here we use whole-genome re-sequencing data to characterize and compare genome-wide patterns of nucleotide polymorphism, site frequency spectrum and population-scaled recombination rates in three species ofPopulus:P. tremula, P. tremuloidesandP. trichocarpa. We find thatP. tremuloideshas the highest level of genome-wide variation, skewed allele frequencies and population-scaled recombination rates, whereasP. trichocarpaharbors the lowest. Our findings highlight multiple lines of evidence suggesting that natural selection, both due to purifying and positive selection, has widely shaped patterns of nucleotide polymorphism at linked neutral sites in all three species. Differences in effective population sizes and rates of recombination are largely explaining the disparate magnitudes and signatures of linked selection we observe among species. The present work provides the first phylogenetic comparative study at genome-wide scale in forest trees. This information will also improve our ability to understand how various evolutionary forces have interacted to influence genome evolution among related species.

scholarly journals Dissecting the Effects of Selection and Mutation on Genetic Diversity in Three Wood White (Leptidea) Butterfly Species

2019 ◽  
Vol 11 (10) ◽  
pp. 2875-2886 ◽  
Author(s):  
Venkat Talla ◽  
Lucile Soler ◽  
Takeshi Kawakami ◽  
Vlad Dincă ◽  
Roger Vila ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Natural Selection ◽  
Nucleotide Diversity ◽  
Gene Annotation ◽  
Rate Variation ◽  
Butterfly Species ◽  
Relative Role ◽  
Effective Population ◽  
Genome Wide ◽  
Population Sizes

Abstract The relative role of natural selection and genetic drift in evolution is a major topic of debate in evolutionary biology. Most knowledge spring from a small group of organisms and originate from before it was possible to generate genome-wide data on genetic variation. Hence, it is necessary to extend to a larger number of taxonomic groups, descriptive and hypothesis-based research aiming at understanding the proximate and ultimate mechanisms underlying both levels of genetic polymorphism and the efficiency of natural selection. In this study, we used data from 60 whole-genome resequenced individuals of three cryptic butterfly species (Leptidea sp.), together with novel gene annotation information and population recombination data. We characterized the overall prevalence of natural selection and investigated the effects of mutation and linked selection on regional variation in nucleotide diversity. Our analyses showed that genome-wide diversity and rate of adaptive substitutions were comparatively low, whereas nonsynonymous to synonymous polymorphism and substitution levels were comparatively high in Leptidea, suggesting small long-term effective population sizes. Still, negative selection on linked sites (background selection) has resulted in reduced nucleotide diversity in regions with relatively high gene density and low recombination rate. We also found a significant effect of mutation rate variation on levels of polymorphism. Finally, there were considerable population differences in levels of genetic diversity and pervasiveness of selection against slightly deleterious alleles, in line with expectations from differences in estimated effective population sizes.

scholarly journals Demography and natural selection have shaped genome-wide variation in the widely distributed conifer Norway Spruce (Picea abies)

2019 ◽  
Author(s):  
Xi Wang ◽  
Carolina Bernhardsson ◽  
Pär K. Ingvarsson
Keyword(s):  
Genetic Diversity ◽  
Natural Selection ◽  
Picea Abies ◽  
Population Size ◽  
Effective Population Size ◽  
Norway Spruce ◽  
Demographic History ◽  
Sequencing Data ◽  
Effective Population ◽  
Genome Wide

AbstractUnder the neutral theory, species with larger effective population sizes are expected to harbour higher genetic diversity. However, across a wide variety of organisms, the range of genetic diversity is orders of magnitude more narrow than the range of effective population size. This observation has become known as Lewontin’s paradox and although aspects of this phenomenon have been extensively studied, the underlying causes for the paradox remain unclear. Norway spruce (Picea abies) is a widely distributed conifer species across the northern hemisphere and it consequently plays a major role in European forestry. Here, we use whole-genome re-sequencing data from 35 individuals to perform population genomic analyses in P. abies in an effort to understand what drives genome-wide patterns of variation in this species. Despite having a very wide geographic distribution and an enormous current population size, our analyses find that genetic diversity of P.abies is low across a number of populations (p=0.005-0.006). To assess the reasons for the low levels of genetic diversity, we infer the demographic history of the species and find that it is characterised by several re-occurring bottlenecks with concomitant decreases in effective population size can, at least partly, provide an explanation for low polymorphism we observe in P. abies. Further analyses suggest that recurrent natural selection, both purifying and positive selection, can also contribute to the loss of genetic diversity in Norway spruce by reducing genetic diversity at linked sites. Finally, the overall low mutation rates seen in conifers can also help explain the low genetic diversity maintained in Norway spruce.

scholarly journals Island songbirds as windows into evolution in small populations

2020 ◽  
Author(s):  
Thibault Leroy ◽  
Marjolaine Rousselle ◽  
Marie-Ka Tilak ◽  
Aude Caizergues ◽  
Celine Scornavacca ◽  
...  
Keyword(s):  
Natural Selection ◽  
Bird Species ◽  
Empirical Support ◽  
Sequence Evolution ◽  
Large Set ◽  
Deleterious Mutations ◽  
Effective Population ◽  
Evolutionary Forces ◽  
Island Species ◽  
Population Sizes

Due to their limited ranges and inherent isolation, island species have long been recognized as crucial systems for tackling a range of evolutionary questions, including in the early study of speciation. Such species have been less studied in the understanding of the evolutionary forces driving DNA sequence evolution. Island species usually have lower census population sizes (N) than continental species and, supposedly, lower effective population sizes (Ne). Given that both the rates of change caused by genetic drift and by selection are dependent upon Ne, island species are theoretically expected to exhibit (i) lower genetic diversity, (ii) less effective natural selection against slightly deleterious mutations, and (iii) a lower rate of adaptive evolution. Here, we have used a large set of newly sequenced and published whole genome sequences of Passerida bird species or subspecies (14 insular and 11 continental) to test these predictions. We empirically confirm that island species exhibit lower census size and Ne, supporting the hypothesis that the smaller area available on islands constrains the upper bound of Ne. In the insular species, we find significantly lower nucleotide diversity in coding regions, higher ratios of non-synonymous to synonymous polymorphisms, and lower adaptive substitution rates. Our results provide robust evidence that the lower Ne experienced by island species has affected both the ability of natural selection to efficiently remove weakly deleterious mutations and also the adaptive potential of island species, therefore providing considerable empirical support for the nearly neutral theory. We discuss the implications for both evolutionary and conservation biology.

scholarly journals Large Number of Replacement Polymorphisms in Rapidly Evolving Genes of Drosophila: Implications for Genome-Wide Surveys of DNA Polymorphism

Genetics ◽  
1999 ◽  
Vol 153 (4) ◽  
pp. 1717-1729 ◽  
Author(s):  
Karl J Schmid ◽  
Loredana Nigro ◽  
Charles F Aquadro ◽  
Diethard Tautz
Keyword(s):  
Recombination Rate ◽  
Current Knowledge ◽  
Purifying Selection ◽  
Neutral Evolution ◽  
Nucleotide Polymorphism ◽  
Effective Population ◽  
Nucleotide Substitutions ◽  
Large Numbers ◽  
Genome Wide ◽  
Population Sizes

AbstractWe present a survey of nucleotide polymorphism of three novel, rapidly evolving genes in populations of Drosophila melanogaster and D. simulans. Levels of silent polymorphism are comparable to other loci, but the number of replacement polymorphisms is higher than that in most other genes surveyed in D. melanogaster and D. simulans. Tests of neutrality fail to reject neutral evolution with one exception. This concerns a gene located in a region of high recombination rate in D. simulans and in a region of low recombination rate in D. melanogaster, due to an inversion. In the latter case it shows a very low number of polymorphisms, presumably due to selective sweeps in the region. Patterns of nucleotide polymorphism suggest that most substitutions are neutral or nearly neutral and that weak (positive and purifying) selection plays a significant role in the evolution of these genes. At all three loci, purifying selection of slightly deleterious replacement mutations appears to be more efficient in D. simulans than in D. melanogaster, presumably due to different effective population sizes. Our analysis suggests that current knowledge about genome-wide patterns of nucleotide polymorphism is far from complete with respect to the types and range of nucleotide substitutions and that further analysis of differences between local populations will be required to understand the forces more completely. We note that rapidly diverging and nearly neutrally evolving genes cannot be expected only in the genome of Drosophila, but are likely to occur in large numbers also in other organisms and that their function and evolution are little understood so far.

scholarly journals Genomic Analysis of the Only Blind Cichlid Reveals Extensive Inactivation in Eye and Pigment Formation Genes

2020 ◽  
Vol 12 (8) ◽  
pp. 1392-1406
Author(s):  
Matthew L Aardema ◽  
Melanie L J Stiassny ◽  
S Elizabeth Alter
Keyword(s):  
Statistical Power ◽  
Genomic Analysis ◽  
Branch Length ◽  
Directional Selection ◽  
Effective Population ◽  
Pigment Formation ◽  
Evolutionary Forces ◽  
Genome Wide ◽  
Population Sizes ◽  
Inactivating Mutations

Abstract Trait loss represents an intriguing evolutionary problem, particularly when it occurs across independent lineages. Fishes in light-poor environments often evolve “troglomorphic” traits, including reduction or loss of both pigment and eyes. Here, we investigate the genomic basis of trait loss in a blind and depigmented African cichlid, Lamprologus lethops, and explore evolutionary forces (selection and drift) that may have contributed to these losses. This species, the only known blind cichlid, is endemic to the lower Congo River. Available evidence suggests that it inhabits deep, low-light habitats. Using genome sequencing, we show that genes related to eye formation and pigmentation, as well as other traits associated with troglomorphism, accumulated inactivating mutations rapidly after speciation. A number of the genes affected in L. lethops are also implicated in troglomorphic phenotypes in Mexican cavefish (Astyanax mexicanus) and other species. Analysis of heterozygosity patterns across the genome indicates that L. lethops underwent a significant population bottleneck roughly 1 Ma, after which effective population sizes remained low. Branch-length tests on a subset of genes with inactivating mutations show little evidence of directional selection; however, low overall heterozygosity may reduce statistical power to detect such signals. Overall, genome-wide patterns suggest that accelerated genetic drift from a severe bottleneck, perhaps aided by directional selection for the loss of physiologically expensive traits, caused inactivating mutations to fix rapidly in this species.

scholarly journals On the estimation of ancestral population sizes of modern humans

1997 ◽  
Vol 69 (2) ◽  
pp. 111-116 ◽  
Author(s):  
ZIHENG YANG
Keyword(s):  
Population Size ◽  
Sequence Data ◽  
Divergence Time ◽  
Ancestral Population ◽  
Rate Variation ◽  
Effective Population ◽  
Modern Humans ◽  
Extant Species ◽  
Population Sizes ◽  
Highly Correlated

The theory developed by Takahata and colleagues for estimating the effective population size of ancestral species using homologous sequences from closely related extant species was extended to take account of variation of evolutionary rates among loci. Nuclear sequence data related to the evolution of modern humans were reanalysed and computer simulations were performed to examine the effect of rate variation on estimation of ancestral population sizes. It is found that the among-locus rate variation does not have a significant effect on estimation of the current population size when sequences from multiple loci are sampled from the same species, but does have a significant effect on estimation of the ancestral population size using sequences from different species. The effects of ancestral population size, species divergence time and among-locus rate variation are found to be highly correlated, and to achieve reliable estimates of the ancestral population size, effects of the other two factors should be estimated independently.

scholarly journals The formation of avian montane diversity across barriers and along elevational gradients

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
José Martín Pujolar ◽  
Mozes P. K. Blom ◽  
Andrew Hart Reeve ◽  
Jonathan D. Kennedy ◽  
Petter Zahl Marki ◽  
...  
Keyword(s):  
Gene Flow ◽  
Population Differentiation ◽  
Bird Species ◽  
Geographic Area ◽  
Effective Population ◽  
Tropical Mountains ◽  
Mountainous Regions ◽  
Pleistocene Climate ◽  
Genome Wide ◽  
Population Sizes

AbstractTropical mountains harbor exceptional concentrations of Earth’s biodiversity. In topographically complex landscapes, montane species typically inhabit multiple mountainous regions, but are absent in intervening lowland environments. Here we report a comparative analysis of genome-wide DNA polymorphism data for population pairs from eighteen Indo-Pacific bird species from the Moluccan islands of Buru and Seram and from across the island of New Guinea. We test how barrier strength and relative elevational distribution predict population differentiation, rates of historical gene flow, and changes in effective population sizes through time. We find population differentiation to be consistently and positively correlated with barrier strength and a species’ altitudinal floor. Additionally, we find that Pleistocene climate oscillations have had a dramatic influence on the demographics of all species but were most pronounced in regions of smaller geographic area. Surprisingly, even the most divergent taxon pairs at the highest elevations experience gene flow across barriers, implying that dispersal between montane regions is important for the formation of montane assemblages.

scholarly journals Robust detection of natural selection using a probabilistic model of tree imbalance

2021 ◽  
Author(s):  
Enes Dilber ◽  
Jonathan Terhorst
Keyword(s):  
Natural Selection ◽  
Open Source Software ◽  
Probabilistic Model ◽  
Simulated Data ◽  
Population Expansion ◽  
Effective Population ◽  
Robust Detection ◽  
Evolutionary Forces ◽  
Tree Topologies ◽  
Neutrality Tests

Neutrality tests such as Tajima's D and Fay and Wu's H are standard implements in the population genetics toolbox. One of their most common uses is to scan the genome for signals of natural selection. However, it is well understood that deviance measures like D and H are confounded by other evolutionary forces---in particular, population expansion---that may be unrelated to selection. Because they are not model-based, it is not clear how to deconfound these statistics in a principled way. In this paper we derive new likelihood-based methods for detecting natural selection which are robust to confounding by fluctuations in effective population size. At the core of our method is a novel probabilistic model of tree imbalance, which generalizes Kingman's coalescent to allow certain aberrant tree topologies to arise more frequently than is expected under neutrality. We derive a frequency spectrum-based estimator which can be used in place of D, and also extend to the case where genealogies are first estimated. We benchmark our methods on real and simulated data, and provide an open source software implementation.

scholarly journals Heterogeneity in effective size across the genome: effects on the Inverse Instantaneous Coalescence Rate (IICR) and implications for demographic inference under linked selection.

2021 ◽  
Author(s):  
Simon Boitard ◽  
Armando Arredondo ◽  
Camille Noûs ◽  
Lounes Chikhi ◽  
Olivier Mazet
Keyword(s):  
Genetic Diversity ◽  
Balancing Selection ◽  
Effective Population ◽  
Recombination Rates ◽  
Genome Wide ◽  
Coalescence Rate ◽  
Demographic Inference ◽  
The Impact ◽  
Linked Selection ◽  
Coalescence Times

The relative contribution of selection and neutrality in shaping species genetic diversity is one of the most central and controversial questions in evolutionary theory. Genomic data provide growing evidence that linked selection, i.e. the modification of genetic diversity at neutral sites through linkage with selected sites, might be pervasive over the genome. Several studies proposed that linked selection could be modelled as first approximation by a local reduction (e.g. purifying selection, selective sweeps) or increase (e.g. balancing selection) of effective population size (Ne). At the genome-wide scale, this leads to a large variance of Ne from one region to another, reflecting the heterogeneity of selective constraints and recombination rates between regions. We investigate here the consequences of this variation of Ne on the genome-wide distribution of coalescence times. The underlying motivation concerns the impact of linked selection on demographic inference, because the distribution of coalescence times is at the heart of several important demographic inference approaches. Using the concept of Inverse Instantaneous Coalescence Rate, we demonstrate that in a panmictic population, linked selection always results in a spurious apparent decrease of Ne along time. Balancing selection has a particularly large effect, even when it concerns a very small part of the genome. We quantify the expected magnitude of the spurious decrease of Ne in humans and Drosophila melanogaster, based on Ne distributions inferred from real data in these species. We also find that the effect of linked selection can be significantly reduced by that of population structure.

scholarly journals The theory and practice of measuring broad-range recombination rate from marker selected pools

2019 ◽  
Author(s):  
Kevin H.-C. Wei ◽  
Aditya Mantha ◽  
Doris Bachtrog
Keyword(s):  
Genetic Distance ◽  
Allele Frequency ◽  
Recombination Rate ◽  
High Throughput Sequencing ◽  
Genetic Material ◽  
Cost Effective ◽  
Theory And Practice ◽  
Rate Variation ◽  
Sequencing Data ◽  
Genome Wide

ABSTRACTRecombination is the exchange of genetic material between homologous chromosomes via physical crossovers. Pioneered by T. H. Morgan and A. Sturtevant over a century ago, methods to estimate recombination rate and genetic distance require scoring large number of recombinant individuals between molecular or visible markers. While high throughput sequencing methods have allowed for genome wide crossover detection producing high resolution maps, such methods rely on large number of recombinants individually sequenced and are therefore difficult to scale. Here, we present a simple and scalable method to infer near chromosome-wide recombination rate from marker selected pools and the corresponding analytical software MarSuPial. Rather than genotyping individuals from recombinant backcrosses, we bulk sequence marker selected pools to infer the allele frequency decay around the selected locus; since the number of recombinant individuals increases proportionally to the genetic distance from the selected locus, the allele frequency across the chromosome can be used to estimate the genetic distance and recombination rate. We mathematically demonstrate the relationship between allele frequency attenuation, recombinant fraction, genetic distance, and recombination rate in marker selected pools. Based on available chromosome-wide recombination rate models of Drosophila, we simulated read counts and determined that nonlinear local regressions (LOESS) produce robust estimates despite the high noise inherent to sequencing data. To empirically validate this approach, we show that (single) marker selected pools closely recapitulate genetic distances inferred from scoring recombinants between double markers. We theoretically determine how secondary loci with viability impacts can modulate the allele frequency decay and how to account for such effects directly from the data. We generated the recombinant map of three wild derived strains which strongly correlates with previous genome-wide measurements. Interestingly, amidst extensive recombination rate variation, multiple regions of the genomes show elevated rates across all strains. Lastly, we apply this method to estimate chromosome-wide crossover interference. Altogether, we find that marker selected pools is a simple and cost effective method for broad recombination rate estimates. Although it does not identify instances of crossovers, it can generate near chromosome-wide recombination maps in as little as one or two libraries.

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