scholarly journals Hydrodynamic flow and concentration gradients in the gut enhance neutral bacterial diversity

2021 ◽  
Vol 119 (1) ◽  
pp. e2108671119
Author(s):  
Darka Labavić ◽  
Claude Loverdo ◽  
Anne-Florence Bitbol
Keyword(s):  
Population Size ◽  
Hydrodynamic Flow ◽  
Mixed System ◽  
Fixation Probability ◽  
Effective Population ◽  
Concentration Gradients ◽  
Active Population ◽  
Spatial Features ◽  
Bacterial Mutants ◽  
Bacterial Concentrations

The gut microbiota features important genetic diversity, and the specific spatial features of the gut may shape evolution within this environment. We investigate the fixation probability of neutral bacterial mutants within a minimal model of the gut that includes hydrodynamic flow and resulting gradients of food and bacterial concentrations. We find that this fixation probability is substantially increased, compared with an equivalent well-mixed system, in the regime where the profiles of food and bacterial concentration are strongly spatially dependent. Fixation probability then becomes independent of total population size. We show that our results can be rationalized by introducing an active population, which consists of those bacteria that are actively consuming food and dividing. The active population size yields an effective population size for neutral mutant fixation probability in the gut.

scholarly journals Hydrodynamic flow and concentration gradients in the gut enhance neutral bacterial diversity

2021 ◽  
Author(s):  
Darka Labavic ◽  
Claude Loverdo ◽  
Anne-Florence Bitbol
Keyword(s):  
Population Size ◽  
Hydrodynamic Flow ◽  
Mixed System ◽  
Fixation Probability ◽  
Effective Population ◽  
Concentration Gradients ◽  
Active Population ◽  
Spatial Features ◽  
Bacterial Mutants ◽  
Bacterial Concentrations

The gut microbiota features important genetic diversity, and the specific spatial features of the gut may shape evolution within this environment. We investigate the fixation probability of neutral bacterial mutants within a minimal model of the gut that includes hydrodynamic flow and resulting gradients of food and bacterial concentrations. We find that this fixation probability is substantially increased compared to an equivalent well-mixed system, in the regime where the profiles of food and bacterial concentration are strongly spatially-dependent. Fixation probability then becomes independent of total population size. We show that our results can be rationalized by introducing an active population, which consists of those bacteria that are actively consuming food and dividing. The active population size yields an effective population size for neutral mutant fixation probability in the gut.

scholarly journals Fixation probability of beneficial mutations in a fluctuating population

2009 ◽  
Vol 91 (1) ◽  
pp. 73-82 ◽  
Author(s):  
STEINAR ENGEN ◽  
RUSSELL LANDE ◽  
BERNT-ERIK SÆTHER
Keyword(s):  
Population Size ◽  
Logistic Model ◽  
Return Time ◽  
Fixation Probability ◽  
Population Fluctuations ◽  
Effective Population ◽  
Environmental Variance ◽  
Fixation Rate ◽  
Beneficial Mutations ◽  
Probability Of Fixation

SummaryWe compute an accurate approximation to the probability of fixation for a beneficial mutation in a population fluctuating with a stationary distribution of population size. The population dynamics are described by the theta-logistic model with environmental variance, assuming that the population size is large enough to ignore demographic variance. We show that stochastic fluctuations of population size reduce the probability of fixation. However, it is not the magnitude of the population fluctuationsper sethat creates this reduction. Only the environmental variance has a substantial effect on the probability of fixation. The strength of density dependence (or expected return time to equilibrium) and the functional form of density-regulation, given by the parameter θ in the theta-logistic model, have little effect on the fixation probability. Effective population size based on harmonic mean population size will therefore underestimate the expected fixation rate of beneficial mutations in fluctuating populations.

scholarly journals The probability of fixation of a favoured allele in a subdivided population

1993 ◽  
Vol 62 (2) ◽  
pp. 149-157 ◽  
Author(s):  
N. H. Barton
Keyword(s):  
Population Structure ◽  
Population Size ◽  
Discrete Model ◽  
Fixation Probability ◽  
Effective Population ◽  
Weak Selection ◽  
Extinction Rates ◽  
Subdivided Population ◽  
Probability Of Fixation ◽  
Neutral Markers

SummaryIn a stably subdivided population with symmetric migration, the chance that a favoured allele will be fixed is independent of population structure. However, random extinction introduces an extra component of sampling drift, and reduces the probability of fixation. In this paper, the fixation probability is calculated using the diffusion approximation; comparison with exact solution of the discrete model shows this to be accurate. The key parameters are the rates of selection, migration and extinction, scaled relative to population size (S = 4Ns, M = 4Nm, Λ = 4Nλ); results apply to a haploid model, or to diploids with additive selection. If new colonies derive from many demes, the fixation probability cannot be reduced by more than half. However, if colonies are initially homogeneous, fixation probability can be much reduced. In the limit of low migration and extinction rates (M, Λ ≪ 1), it is 2s/{1 + (Λ/MS)(1 −exp(−S))}, whilst in the opposite limit (S ≪ 1), it is 4sM/{Λ(Λ + M)}. In the limit of weak selection (M, Λ ≫ 1), it is 4sM/{Λ(Λ + M)}. These factors are not the same as the reduction in effective population size (Ne/N), showing that the effects of population structure on selected alleles cannot be understood from the behaviour of neutral markers.

scholarly journals NATURAL SELECTION FOR WITHIN-GENERATION VARIANCE IN OFFSPRING NUMBER

Genetics ◽  
1974 ◽  
Vol 76 (3) ◽  
pp. 601-606
Author(s):  
John H Gillespie
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Population Size ◽  
Effective Population Size ◽  
Variance Component ◽  
Fixation Probability ◽  
Effective Population ◽  
Offspring Number ◽  
Selection For

ABSTRACT In this paper it is shown that natural selection can act on the within-generation variance in offspring number. The fitness of a genotype will increase as its variance in offspring number decreases. The intensity of selection on the variance component is inversely proportional to population size, although the fixation probability of a gene which differs from its allele only in the variance in its offspring number is independent of population size. The concept of effective population size is shown to be of limited use when there is genetic variation in the variance in offspring number.

Evolutionary genetics of small populations

2017 ◽  
Author(s):  
Richard Frankham ◽  
Jonathan D. Ballou ◽  
Katherine Ralls ◽  
Mark D. B. Eldridge ◽  
Michele R. Dudash ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Evolutionary Genetics ◽  
Small Population ◽  
Small Populations ◽  
Effective Population ◽  
Genetic Management ◽  
Evolutionary Genetic ◽  
Loss Of Genetic Diversity ◽  
Number Of Individuals

Genetic management of fragmented populations involves the application of evolutionary genetic theory and knowledge to alleviate problems due to inbreeding and loss of genetic diversity in small population fragments. Populations evolve through the effects of mutation, natural selection, chance (genetic drift) and gene flow (migration). Large outbreeding, sexually reproducing populations typically contain substantial genetic diversity, while small populations typically contain reduced levels. Genetic impacts of small population size on inbreeding, loss of genetic diversity and population differentiation are determined by the genetically effective population size, which is usually much smaller than the number of individuals.

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