scholarly journals The comparative population genetics of Neisseria meningitidis and Neisseria gonorrhoeae

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7216 ◽  
Author(s):  
Lucile Vigué ◽  
Adam Eyre-Walker
Keyword(s):  
Population Genetics ◽  
Gene Transfer ◽  
Neisseria Meningitidis ◽  
Population Size ◽  
Effective Population Size ◽  
Adaptive Evolution ◽  
Lateral Gene Transfer ◽  
Pathogenic Bacteria ◽  
Core Genome ◽  
Effective Population

Neisseria meningitidis and N. gonorrhoeae are closely related pathogenic bacteria. To compare their population genetics, we compiled a dataset of 1,145 genes found across 20 N. meningitidis and 15 N. gonorrhoeae genomes. We find that N. meningitidis is seven-times more diverse than N. gonorrhoeae in their combined core genome. Both species have acquired the majority of their diversity by recombination with divergent strains, however, we find that N. meningitidis has acquired more of its diversity by recombination than N. gonorrhoeae. We find that linkage disequilibrium (LD) declines rapidly across the genomes of both species. Several observations suggest that N. meningitidis has a higher effective population size than N. gonorrhoeae; it is more diverse, the ratio of non-synonymous to synonymous polymorphism is lower, and LD declines more rapidly to a lower asymptote in N. meningitidis. The two species share a modest amount of variation, half of which seems to have been acquired by lateral gene transfer and half from their common ancestor. We investigate whether diversity varies across the genome of each species and find that it does. Much of this variation is due to different levels of lateral gene transfer. However, we also find some evidence that the effective population size varies across the genome. We test for adaptive evolution in the core genome using a McDonald–Kreitman test and by considering the diversity around non-synonymous sites that are fixed for different alleles in the two species. We find some evidence for adaptive evolution using both approaches.

scholarly journals The comparative population genetics of Neisseria meningitidis and Neisseria gonorrhoeae

2018 ◽  
Author(s):  
Lucile Vigue ◽  
Adam Eyre-Walker
Keyword(s):  
Gene Transfer ◽  
Neisseria Meningitidis ◽  
Population Size ◽  
Effective Population Size ◽  
Lateral Gene Transfer ◽  
Pathogenic Bacteria ◽  
Core Genome ◽  
Effective Population ◽  
Synonymous Polymorphism ◽  
20 Nm

Neisseria meningitidis (Nm) and N. gonorrhoeae (Ng) are closely related pathogenic bacteria. Using those genes found across 20 Nm and 15 Ng genomes we find that Nm is 7x more diverse than Ng in their combined core genome. Both species have acquired the majority of their diversity by recombination with divergent strains, however we find that Nm has acquired more of its diversity by recombination than Ng. We find that linkage disequilibrium declines rapidly across both species. Several observations suggest that Nm has a higher effective population size than Ng; it is more diverse, the ratio of non-synonymous to synonymous polymorphism is lower, and LD declines more rapidly to a lower asymptote. The two species share a modest amount of variation, half of which seems to have been acquired by lateral gene transfer and half from their common ancestor. We investigate whether diversity varies across the genome of each species and find that it does. Much of this variation is due to different levels of lateral gene transfer. However, we also find some evidence that the effective population size varies across the genome. We test for adaptive evolution in the core genome and found some evidence.

scholarly journals The comparative population genetics of Neisseria meningitidis and Neisseria gonorrhoeae

2018 ◽  
Author(s):  
Lucile Vigue ◽  
Adam Eyre-Walker
Keyword(s):  
Gene Transfer ◽  
Neisseria Meningitidis ◽  
Population Size ◽  
Effective Population Size ◽  
Lateral Gene Transfer ◽  
Pathogenic Bacteria ◽  
Core Genome ◽  
Effective Population ◽  
Synonymous Polymorphism ◽  
20 Nm

Neisseria meningitidis (Nm) and N. gonorrhoeae (Ng) are closely related pathogenic bacteria. Using those genes found across 20 Nm and 15 Ng genomes we find that Nm is 7x more diverse than Ng in their combined core genome. Both species have acquired the majority of their diversity by recombination with divergent strains, however we find that Nm has acquired more of its diversity by recombination than Ng. We find that linkage disequilibrium declines rapidly across both species. Several observations suggest that Nm has a higher effective population size than Ng; it is more diverse, the ratio of non-synonymous to synonymous polymorphism is lower, and LD declines more rapidly to a lower asymptote. The two species share a modest amount of variation, half of which seems to have been acquired by lateral gene transfer and half from their common ancestor. We investigate whether diversity varies across the genome of each species and find that it does. Much of this variation is due to different levels of lateral gene transfer. However, we also find some evidence that the effective population size varies across the genome. We test for adaptive evolution in the core genome and found some evidence.

scholarly journals The population genetics of haplo-diploids and X-linked genes

1984 ◽  
Vol 44 (3) ◽  
pp. 321-341 ◽  
Author(s):  
P. J. Avery
Keyword(s):  
Population Genetics ◽  
Genetic Variability ◽  
Population Size ◽  
Effective Population Size ◽  
Disease Genes ◽  
Effective Population ◽  
Random Drift ◽  
Mutation Pressure ◽  
Electrophoretic Data ◽  
Fitness Parameters

SUMMARYFrom the available electrophoretic data, it is clear that haplodiploid insects have a much lower level of genetic variability than diploid insects, a difference that is only partially explained by the social structure of some haplodiploid species. The data comparing X-linked genes and autosomal genes in the same species is much more sparse and little can be inferred from it. This data is compared with theoretical analyses of X-linked genes and genes in haplodiploids. (The theoretical population genetics of X-linked genes and genes in haplodiploids are identical.) X-linked genes under directional selection will be lost or fixed more quickly than autosomal genes as selection acts more directly on X-linked genes and the effective population size is smaller. However, deleterious disease genes, maintained by mutation pressure, will give higher disease incidences at X-linked loci and hence rare mutants are easier to detect at X-linked loci. Considering the forces which can maintain balanced polymorphisms, there are much stronger restrictions on the fitness parameters at X-linked loci than at autosomal loci if genetic variability is to be maintained, and thus fewer polymorphic loci are to be expected on the X-chromosome and in haplodiploids. However, the mutation-random drift hypothesis also leads to the expectation of lower heterozygosity due to the decrease in effective population size. Thus the theoretical results fit in with the data but it is still subject to argument whether selection or mutation-random drift are maintaining most of the genetic variability at X-linked genes and genes in haplodiploids.

scholarly journals Adaptive Evolution and Effective Population Size in Wild House Mice

2012 ◽  
Vol 29 (10) ◽  
pp. 2949-2955 ◽  
Author(s):  
M. Phifer-Rixey ◽  
F. Bonhomme ◽  
P. Boursot ◽  
G. A. Churchill ◽  
J. Pialek ◽  
...  
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Adaptive Evolution ◽  
House Mice ◽  
Effective Population ◽  
Wild House Mice

scholarly journals Effective population size for culturally evolving traits

2021 ◽  
Author(s):  
Dominik Deffner ◽  
Anne Kandler ◽  
Laurel Fogarty
Keyword(s):  
Population Genetics ◽  
Social Network ◽  
Cultural Diversity ◽  
Population Size ◽  
Effective Population Size ◽  
Network Structure ◽  
Cultural Exchange ◽  
Effective Size ◽  
Effective Population ◽  
Social Network Structure

ABSTRACTPopulation size has long been considered an important driver of cultural diversity and complexity. Results from population genetics, however, demonstrate that in populations with complex demographic structure or mode of inheritance, it is not the census population size, N, but the effective size of a population, Ne, that determines important evolutionary parameters. Here, we examine the concept of effective population size for traits that evolve culturally, through processes of innovation and social learning. We use mathematical and computational modeling approaches to investigate how cultural Ne and levels of diversity depend on (1) the way traits are learned, (2) population connectedness, and (3) social network structure. We show that one-to-many and frequency-dependent transmission can temporally or permanently lower effective population size compared to census numbers. We caution that migration and cultural exchange can have counter-intuitive effects on Ne. Network density in random networks leaves Ne unchanged, scale-free networks tend to decrease and small-world networks tend to increase Ne compared to census numbers. For one-to-many transmission and different network structures, effective size and cultural diversity are closely associated. For connectedness, however, even small amounts of migration and cultural exchange result in high diversity independently of Ne. Our results highlight the importance of carefully defining effective population size for cultural systems and show that inferring Ne requires detailed knowledge about underlying cultural and demographic processes.AUTHOR SUMMARYHuman populations show immense cultural diversity and researchers have regarded population size as an important driver of cultural variation and complexity. Our approach is based on cultural evolutionary theory which applies ideas about evolution to understand how cultural traits change over time. We employ insights from population genetics about the “effective” size of a population (i.e. the size that matters for important evolutionary outcomes) to understand how and when larger populations can be expected to be more culturally diverse. Specifically, we provide a formal derivation for cultural effective population size and use mathematical and computational models to study how effective size and cultural diversity depend on (1) the way culture is transmitted, (2) levels of migration and cultural exchange, as well as (3) social network structure. Our results highlight the importance of effective sizes for cultural evolution and provide heuristics for empirical researchers to decide when census numbers could be used as proxies for the theoretically relevant effective numbers and when they should not.

Changing Effective Population Size and the McDonald-Kreitman Test

Genetics ◽  
2002 ◽  
Vol 162 (4) ◽  
pp. 2017-2024 ◽  
Author(s):  
Adam Eyre-Walker
Keyword(s):  
Amino Acid ◽  
Positive Selection ◽  
Population Size ◽  
Effective Population Size ◽  
Adaptive Evolution ◽  
Synonymous Codon ◽  
Low Frequency ◽  
Effective Population ◽  
Amino Acid Mutations ◽  
Codon Use

Abstract Artifactual evidence of adaptive amino acid substitution can be generated within a McDonald-Kreitman test if some amino acid mutations are slightly deleterious and there has been an increase in effective population size. Here I investigate the conditions under which this occurs. I show that fairly small increases in effective population size can generate artifactual evidence of positive selection if there is no selection upon synonymous codon use. This problem is exacerbated by the removal of low-frequency polymorphisms. However, selection on synonymous codon use restricts the conditions under which artifactual evidence of adaptive evolution is produced.

scholarly journals Inferring population size history from large samples of genome wide molecular data - an approximate Bayesian computation approach

2016 ◽  
Author(s):  
Simon Boitard ◽  
Willy Rodriguez ◽  
Flora Jay ◽  
Stefano Mona ◽  
Frederic Austeritz
Keyword(s):  
Population Genetics ◽  
Population Size ◽  
Effective Population Size ◽  
Approximate Bayesian Computation ◽  
Recent Common Ancestor ◽  
Bayesian Computation ◽  
Effective Population ◽  
Wide Range ◽  
Complete Genomes ◽  
Approximate Bayesian

Inferring the ancestral dynamics of effective population size is a long-standing question in population genetics, which can now be tackled much more accurately thanks to the massive genomic data available in many species. Several promising methods that take advantage of whole-genome sequences have been recently developed in this context. However, they can only be applied to rather small samples, which limits their ability to estimate recent population size history. Besides, they can be very sensitive to sequencing or phasing errors. Here we introduce a new approximate Bayesian computation approach named PopSizeABC that allows estimating the evolution of the effective population size through time, using a large sample of complete genomes. This sample is summarized using the folded allele frequency spectrum and the average zygotic linkage disequilibrium at different bins of physical distance, two classes of statistics that are widely used in population genetics and can be easily computed from unphased and unpolarized SNP data. Our approach provides accurate estimations of past population sizes, from the very first generations before present back to the expected time to the most recent common ancestor of the sample, as shown by simulations under a wide range of demographic scenarios. When applied to samples of 15 or 25 complete genomes in four cattle breeds (Angus, Fleckvieh, Holstein and Jersey), PopSizeABC revealed a series of population declines, related to historical events such as domestication or modern breed creation. We further highlight that our approach is robust to sequencing errors, provided summary statistics are computed from SNPs with common alleles.

scholarly journals Genetic diversity and structure of two endangered mole salamander species of the Trans-Mexican Volcanic Belt

Herpetozoa ◽  
2019 ◽  
Vol 32 ◽  
pp. 237-248 ◽  
Author(s):  
Octavio Monroy-Vilchis ◽  
Rosa-Laura Heredia-Bobadilla ◽  
Martha M. Zarco-González ◽  
Víctor Ávila-Akerberg ◽  
Armando Sunny
Keyword(s):  
Genetic Diversity ◽  
Population Genetics ◽  
Population Size ◽  
Effective Population Size ◽  
Volcanic Belt ◽  
Population Declines ◽  
Effective Population ◽  
Mexican Volcanic Belt ◽  
Genetic Diversity And Structure ◽  
Trans Mexican Volcanic Belt

The most important factor leading to amphibian population declines and extinctions is habitat degradation and destruction. To help prevent further extinctions, studies are needed to make appropriate conservation decisions in small and fragmented populations. The goal of this study was to provide data from the population genetics of two micro-endemic mole salamanders from the Trans-Mexican Volcanic Belt. Nine microsatellite markers were used to study the population genetics of 152 individuals from two Ambystoma species. We sampled 38 individuals in two localities for A. altamirani and A. rivualre. We found medium to high levels of genetic diversity expressed as heterozygosity in the populations. However, all the populations presented few alleles per locus and genotypes. We found strong genetic structure between populations for each species. Effective population size was small but similar to that of the studies from other mole salamanders with restricted distributions or with recently fragmented habitats. Despite the medium to high levels of genetic diversity expressed as heterozygosity, we found few alleles, evidence of a genetic bottleneck and that the effective population size is small in all populations. Therefore, this study is important to propose better management plans and conservation efforts for these species.

scholarly journals Adaptive Protein Evolution in Animals and the Effective Population Size Hypothesis.

2015 ◽  
Author(s):  
Nicolas Galtier
Keyword(s):  
Amino Acid ◽  
Population Size ◽  
Effective Population Size ◽  
Adaptive Evolution ◽  
Protein Evolution ◽  
Amino Acid Substitution ◽  
Animal Species ◽  
Effective Population ◽  
Large Populations ◽  
Adaptive Processes

The rate at which genomes adapt to environmental changes and the prevalence of adaptive processes in molecular evolution are two controversial issues in current evolutionary genetics. Previous attempts to quantify the genome-wide rate of adaptation through amino-acid substitution have revealed a surprising diversity of patterns, with some species (e.g. Drosophila) experiencing a very high adaptive rate, while other (e.g. humans) are dominated by nearly-neutral processes. It has been suggested that this discrepancy reflects between-species differences in effective population size. Published studies, however, were mainly focused on model organisms, and relied on disparate data sets and methodologies, so that an overview of the prevalence of adaptive protein evolution in nature is currently lacking. Here we extend existing estimators of the amino-acid adaptive rate by explicitly modelling the effect of favourable mutations on non-synonymous polymorphism patterns, and we apply these methods to a newly-built, homogeneous data set of 44 non-model animal species pairs. Data analysis uncovers a major contribution of adaptive evolution to the amino-acid substitution process across all major metazoan phyla - with the notable exception of humans and primates. The proportion of adaptive amino-acid substitution is found to be positively correlated to species effective population size. This relationship, however, appears to be primarily driven by a decreased rate of nearly-neutral amino-acid substitution due to more efficient purifying selection in large populations. Our results reveal that adaptive processes dominate the evolution of proteins in most animal species, but do not corroborate the hypothesis that adaptive substitutions accumulate at a faster rate in large populations. Implications regarding the factors influencing the rate of adaptive evolution and positive selection detection in humans vs. other organisms are discussed.

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