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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.Positive Frequency-Dependent SelectionIn positive...

Limits to Natural Selection

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...

What is Population Genetics?

What is Population Genetics?

A population is composed of members of the same species that simultaneously live and interact in the same area. When individuals in a population breed, they pass down their genes to their offspring. Many of these genes are polymorphic, meaning that they occur in multiple variants. Such variations of a gene are referred to as alleles. The collective set of all the alleles within a population is known as the gene pool.While some alleles of a given gene might be observed commonly, other variants...

Evolutionary Relationships through Genome Comparisons

Evolutionary Relationships through Genome Comparisons

Genome comparison is one of the excellent ways to interpret the evolutionary relationships between organisms. The basic principle of genome comparison is that if two species share a common feature, it is likely encoded by the DNA sequence conserved between both species. The advent of genome sequencing technologies in the late 20th century enabled scientists to understand the concept of conservation of domains between species and helped them to deduce evolutionary relationships across diverse...

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...

Conservation of Small Populations

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less likely to...

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Related Experiment Video

Updated: Jun 8, 2026

Heuristic Mining of Hierarchical Genotypes and Accessory Genome Loci in Bacterial Populations

Heuristic Mining of Hierarchical Genotypes and Accessory Genome Loci in Bacterial Populations

Published on: December 7, 2021

Ecosystem-specific selection pressures revealed through comparative population genomics.

Maureen L Coleman¹, Sallie W Chisholm

¹Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Proceedings of the National Academy of Sciences of the United States of America

|October 13, 2010

Summary

Marine microbes like Prochlorococcus and Pelagibacter show high genetic diversity. Phosphorus availability appears to be a key factor driving adaptive gene evolution in Atlantic populations.

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Last Updated: Jun 8, 2026

Heuristic Mining of Hierarchical Genotypes and Accessory Genome Loci in Bacterial Populations

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Published on: December 7, 2021

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Resurrection of Dormant Daphnia magna: Protocol and Applications

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Published on: January 19, 2018

Area of Science:

Microbial genomics
Marine microbial ecology
Evolutionary biology

Background:

Bacterial populations exhibit extensive genetic diversity shaped by various evolutionary forces.
Understanding the adaptive versus neutral basis of gene content variation within microbial populations is crucial.

Purpose of the Study:

To quantify gene content heterogeneity in Prochlorococcus and Pelagibacter populations across ocean basins.
To identify selective pressures driving divergence in marine microbial "population genomes".

Main Methods:

Comparative genomics of Prochlorococcus and Pelagibacter from Atlantic and Pacific Oceans.
Analysis of gene abundance and phylogenetic clustering to infer adaptive evolution.

Main Results:

A substantial fraction of genes were rare within each population, indicating ongoing gene transfer and loss.
Few genes differed significantly in abundance between Atlantic and Pacific populations.
Genes related to phosphorus acquisition were enriched in the Atlantic and showed distinct phylogenetic clustering, unlike housekeeping genes.

Conclusions:

Phosphorus availability is a major selective force driving divergence between Atlantic and Pacific marine microbial populations.
The study demonstrates a powerful approach for identifying selective agents in microbial systems.