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Speciation Rates

Speciation Rates

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.

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...

Life Histories

Life Histories

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.

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).

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Related Experiment Video

Updated: Jan 9, 2026

Maintaining Biological Cultures and Measuring Gene Expression in Aphis nerii: A Non-model System for Plant-insect Interactions

Maintaining Biological Cultures and Measuring Gene Expression in Aphis nerii: A Non-model System for Plant-insect Interactions

Published on: August 31, 2018

Life Cycle Simplifications in Aphids Drive Changes in Evolutionary Rates and Selection Regimes.

T Vericel¹, G Gong¹, F Legeai¹

¹UMR 1349 IGEPP, INRAE, Le Rheu 35650, France.

Molecular Biology and Evolution

|December 1, 2025

Summary

This summary is machine-generated.

Simplified aphid life cycles (monoecy) lead to faster molecular evolution due to relaxed selection on genes. This contrasts with complex life cycles (heteroecy), which show intensified selection, impacting evolutionary trajectories.

Keywords:

aphids comparative genomics dN/dS host alternation life cycle transition

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Published on: November 1, 2017

Area of Science:

Evolutionary biology
Genomics
Molecular evolution

Background:

Aphids exhibit complex life cycles involving host alternation (heteroecy) or simplified cycles (monoecy).
The impact of life cycle simplification on the rate of molecular evolution is not well understood.

Purpose of the Study:

To investigate how transitions from heteroecy to monoecy affect evolutionary dynamics at the gene level in aphids.
To determine if life cycle simplification alters selection pressures on genes.

Main Methods:

Comparative genomics analysis of 46 aphid species.
Identification of 9,304 orthologs.
Estimation of evolutionary rates (dN/dS) and selection regimes.

Main Results:

715 orthologs showed faster evolution in monoecious species, linked to relaxed selection.
Heteroecious species displayed signatures of intensified selection.
Genes under relaxed selection in monoecious species are involved in environmental sensing, signaling, and host alternation traits.

Conclusions:

Loss of complex life cycles in aphids leads to reduced selective constraints and ecological simplification.
Life cycle transitions significantly shape molecular evolution and can drive gene decay.