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Hardy-Weinberg Principle

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.

Types of Selection

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...

Genetic Drift

Genetic Drift

Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.

Mutation, Gene Flow, and Genetic Drift

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

Distribution and Dispersion

Distribution and Dispersion

To understand intra-specific interactions in populations, scientists measure the spatial arrangement of species individuals. This geographic arrangement is known as the species distribution or dispersion. Highly territorial species exhibit a uniform distribution pattern, in which individuals are spaced at relatively equal distances from one another. Species that are highly tied to particular resources, such as food or shelter, tend to concentrate around those resources, and thus exhibit a...

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Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli

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THE EVOLUTIONARILY STABLE PHENOTYPE DISTRIBUTION IN A RANDOM ENVIRONMENT.

Akira Sasaki¹, Stephen Ellner²

¹Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812, Japan.

Evolution; International Journal of Organic Evolution

|June 1, 2017

Summary

Phenotypic variability can be a bet-hedging strategy in changing environments. Evolutionarily stable distributions are often discrete, with more phenotypes emerging as environmental fluctuations increase.

Keywords:

Bet-hedging evolutionarily stable strategy (ESS)genetic polymorphism phenotypic variation random environment

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Area of Science:

Evolutionary biology
Population genetics
Theoretical ecology

Background:

Phenotypic variability can serve as a bet-hedging strategy in unpredictable environments.
Understanding evolutionarily stable phenotype distributions under fluctuating selection is crucial.

Purpose of the Study:

To examine two models of evolutionarily stable phenotype distributions under stabilizing selection with a fluctuating optimum.
To investigate the impact of generational overlap and environmental variance on these distributions.

Main Methods:

Developed two models: a mixed-strategies model (offspring with a distribution of phenotypes) and a pure-strategies model (offspring with a single, genetically determined phenotype).
Analyzed models with overlapping generations, considering adult survival or a dormant propagule pool.
Investigated conditions for evolutionarily stable strategies (ESS) and the nature of phenotype distributions (discrete vs. continuous, monomorphic vs. polymorphic).

Main Results:

In the mixed-strategies model, the ESS distribution is unique, independent of generational overlap, and generically discrete.
ESS can be monomorphic (single phenotype) under low environmental variability, becoming polymorphic (multiple phenotypes) with increased variability.
The pure-strategies model also yields discrete phenotype distributions, with more distinct phenotypes appearing as environmental variance rises.

Conclusions:

Phenotypic variability, as a bet-hedging strategy, leads to discrete, evolutionarily stable phenotype distributions.
The structure of these distributions (monomorphic, dimorphic, or with infinite phenotypes) depends on the level and type of environmental fluctuation.
Both mixed and pure strategies in offspring production result in similar patterns of discrete phenotypic distributions under increasing environmental variance.