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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.

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...

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).

Speciation Rates

Speciation Rates

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.

What is Natural Selection?

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.

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Related Experiment Video

Updated: Jun 16, 2025

Rearing and Long-Term Maintenance of Eristalis tenax Hoverflies for Research Studies

Rearing and Long-Term Maintenance of Eristalis tenax Hoverflies for Research Studies

Published on: May 19, 2018

Fluctuating selection among years in a wild insect.

Rolando Rodríguez-Muñoz¹, Paul E Hopwood¹, Jon Slate²

¹Centre for Ecology & Conservation, University of Exeter, Penryn Campus, Penryn, United Kingdom.

Evolution; International Journal of Organic Evolution

|March 4, 2025

Summary

This summary is machine-generated.

Variation in natural selection is crucial for understanding evolution. A 10-year study on field crickets (Gryllus campestris) revealed significant yearly shifts in selection pressures on various traits, highlighting the dynamic nature of evolution in wild populations.

Keywords:

Gryllus campestris genetic variation lifespan mating rate polyandry selection gradient

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Area of Science:

Evolutionary Biology
Ecology
Animal Behavior

Background:

Temporal and spatial variation in selection can resolve evolutionary puzzles like stasis and genetic variation maintenance.
Multigenerational selection data in wild invertebrates are limited, despite their likely sensitivity to environmental changes.
Short-lived ectotherms are hypothesized to experience greater intergenerational environmental variation, making selection dynamics significant.

Purpose of the Study:

To investigate multigenerational variation in selection pressures in a wild invertebrate population.
To quantify selection gradients on multiple traits over a decade in a field cricket population.
To determine if selection directionality fluctuates across generations in response to environmental changes.

Main Methods:

A 10-year field study of an individually tagged Gryllus campestris population.
Utilized a network of 133 day-night video cameras to collect over a million hours of behavioral and life-history data.
Assigned parentage using genetic markers to measure individual fitness (number of adult offspring) and calculate selection gradients on traits like emergence date, body size, and lifespan.

Main Results:

Observed substantial variation in selection gradients across years for multiple traits in the cricket population.
Documented significant annual differences in average trait values, including adult emergence date, body size, and lifespan.
Found evidence of selection switching from positive to negative for adult emergence date over the study period.

Conclusions:

Fluctuations in selection gradients appear common in wild invertebrate populations.
While selection can vary considerably year-to-year, complete reversals in selection direction may be infrequent.
This study provides crucial long-term, multigenerational data on selection in wild invertebrates, informing evolutionary theory.