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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...

Genetics of Speciation

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.

Speciation Rates

Speciation Rates

Hybrid Zones

Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may possess distinct phenotypic or genetic differences that impact their survival and reproductive success. The genetic variances introduced by hybridization influence species diversity and speciation processes within the hybrid zone.

Trihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...

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Related Experiment Video

Updated: May 27, 2026

Live Imaging Characterization of Centromere Movements During Male Meiotic Prophase in Arabidopsis thaliana

Live Imaging Characterization of Centromere Movements During Male Meiotic Prophase in Arabidopsis thaliana

Published on: October 24, 2025

Competition between cytotypes changes across a longitudinal gradient in Centaurea stoebe (Asteraceae).

Alexandra R Collins¹, Ruhollah Naderi, Heinz Mueller-Schaerer

¹University of Fribourg, Ecology and Evolution Department, Fribourg, Switzerland. robin.collins@unifr.ch

American Journal of Botany

|November 15, 2011

Summary

Polyploid plants (tetraploids) did not outperform diploids in biomass but showed better long-term persistence traits. Their competitive ability varied geographically, suggesting polyploid establishment depends on location and interactions with diploids.

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Area of Science:

Plant evolutionary biology
Ecology
Genetics

Background:

Polyploidy, arising from whole genome duplication, is a significant driver of plant adaptive evolution.
Successful establishment of polyploids alongside diploid progenitors often requires competitive superiority.
Understanding the conditions for polyploid persistence is crucial for plant speciation and evolution.

Purpose of the Study:

To investigate the competitive interactions between diploid and tetraploid cytotypes of Centaurea stoebe.
To determine if tetraploids possess greater competitive ability than diploids.
To assess how competitive abilities vary with population type (single- vs. mixed-cytotype) and along a longitudinal gradient.

Main Methods:

Conducted pairwise competition experiments between diploid and tetraploid Centaurea stoebe.
Compared aboveground biomass, belowground biomass allocation, and traits related to long-term persistence.
Analyzed competitive abilities across different sampling localities in Europe, considering single- and mixed-cytotype populations.

Main Results:

Tetraploids did not show greater aboveground biomass but allocated more biomass belowground compared to diploids.
Tetraploids exhibited enhanced long-term persistence traits, including more frequent bolting and accessory rosette production.
Competitive ability of tetraploids varied geographically, being stronger in Western Europe than in Eastern Europe, suggesting regional differences in inter-cytotype competition.

Conclusions:

Competitive interactions between plant cytotypes are not uniform across their distributional range.
Geographic variation in competitive ability influences the potential for polyploid establishment and coexistence with diploids.
Examining competitive dynamics across diverse localities is essential for understanding polyploid evolution and persistence.