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Related Concept Videos

Types of Selection01:46

Types of Selection

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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...
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Gene Flow02:39

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Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.
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Frequency-dependent Selection01:21

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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.
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Osmoregulation in Fishes02:32

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When cells are placed in a hypotonic (low-salt) fluid, they can swell and burst. Meanwhile, cells in a hypertonic solution—with a higher salt concentration—can shrivel and die. How do fish cells avoid these gruesome fates in hypotonic freshwater or hypertonic seawater environments?
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Fixed Action Patterns01:06

Fixed Action Patterns

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A fixed action pattern (FAP) is a specific, hard-wired sequence of behaviors that occurs in response to an external stimulus, called a sign stimulus. The behavior is “fixed” because it is essentially unchangeable—proceeding similarly across individuals of a species every time it occurs.
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Limits to Natural Selection01:38

Limits to Natural Selection

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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.
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Related Experiment Video

Updated: Apr 27, 2026

Implantation of a New Micro Acoustic Tag in Juvenile Pacific Lamprey and American Eel
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Do North Atlantic eels show parallel patterns of spatially varying selection?

Malene G Ulrik, José Martín Pujolar, Anne-Laure Ferchaud

  • 1Department of Bioscience, Aarhus University, Ny Munkegade 114, Bldg, 1540, DK-8000 Aarhus C, Denmark. michael.m.hansen@biology.au.dk.

BMC Evolutionary Biology
|June 21, 2014
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Summary

Genetic analysis of European eels reveals 11 genes under selection, primarily involved in metabolism and defense. Unlike American eels, temperature showed little correlation, suggesting diverse environmental pressures shape these closely related species.

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Area of Science:

  • Evolutionary biology
  • Population genetics
  • Ecology

Background:

  • European and American eels are sister species with gene flow, ideal for studying parallel selection.
  • A panel of 80 coding-gene SNPs was used to genotype European eels across 8 locations.
  • The study investigated single-generation signatures of spatially varying selection in European eel.

Purpose of the Study:

  • To identify genes under selection in European eel populations.
  • To compare selection patterns between European and American eels.
  • To explore the relationship between allele frequencies and environmental variables.

Main Methods:

  • Genotyping of European eel (glass eels) using 80 coding-gene SNPs.
  • FST-based outlier tests to detect elevated genetic differentiation.
  • Association analysis between allele frequencies and environmental variables.

Main Results:

  • Signatures of selection were found at 11 coding-gene SNPs.
  • Candidate genes are mainly involved in metabolism and defense.
  • Only 2 SNPs correlated with temperature, unlike in American eels, suggesting other environmental factors are influential.

Conclusions:

  • Different selection signatures between species may result from distinct selective pressures, potentially linked to larval migration differences.
  • Lack of parallel selection could be due to polygenic traits, reducing the chance of selection acting on the same genes in both species.