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 Recent evolution in Rattus norvegicus is shaped by declining effective population size

2015 ◽  
Author(s):  
Eva E Deinum ◽  
Daniel L Halligan ◽  
Rob W Ness ◽  
Yao-Hua Zhang ◽  
Lin Cong ◽  
...  
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Rattus Norvegicus ◽  
Demographic History ◽  
Physical Distance ◽  
House Mice ◽  
Effective Population ◽  
Genome Sequences ◽  
Wild House Mice ◽  
Wild Rats

The brown rat, Rattus norvegicus, is both a notorious pest and a frequently used model in biomedical research. By analysing genome sequences of 12 wild-caught brown rats from their ancestral range in NE China, along with the sequence of a black rat, R. rattus, we investigate the selective and demographic forces shaping variation in the genome. We estimate that the recent effective population size (N_e) of this species = 1.24 x 10^5, based on silent site diversity. We compare patterns of diversity in these genomes with patterns in multiple genome sequences of the house mouse Mus musculus castaneus), which has a much larger N_e. This reveals an important role for variation in the strength of genetic drift in mammalian genome evolution. By a Pairwise Sequentially Markovian Coalescent (PSMC) analysis of demographic history, we infer that there has been a recent population size bottleneck in wild rats, which we date to approximately 20,000 years ago. Consistent with this, wild rat populations have experienced an increased flux of mildly deleterious mutations, which segregate at higher frequencies in protein-coding genes and conserved noncoding elements (CNEs). This leads to negative estimates of the rate of adaptive evolution (alpha) in proteins and CNEs, a result which we discuss in relation to the strongly positive estimates observed in wild house mice. As a consequence of the population bottleneck, wild rats also show a markedly slower decay of linkage disequilibrium with physical distance than wild house mice.

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.

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 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.

scholarly journals A phylogenetic estimator of effective population size or mutation rate.

Genetics ◽  
1994 ◽  
Vol 136 (2) ◽  
pp. 685-692 ◽  
Author(s):  
Y X Fu
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Mutation Rate ◽  
Dna Sequences ◽  
High Efficiency ◽  
Minimum Variance ◽  
Population Subdivision ◽  
Effective Population ◽  
Fisher Model ◽  
Mitochondrial Sequences

Abstract A new estimator of the essential parameter theta = 4Ne mu from DNA polymorphism data is developed under the neutral Wright-Fisher model without recombination and population subdivision, where Ne is the effective population size and mu is the mutation rate per locus per generation. The new estimator has a variance only slightly larger than the minimum variance of all possible unbiased estimators of the parameter and is substantially smaller than that of any existing estimator. The high efficiency of the new estimator is achieved by making full use of phylogenetic information in a sample of DNA sequences from a population. An example of estimating theta by the new method is presented using the mitochondrial sequences from an American Indian population.

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