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Related Concept Videos

What is Natural Selection?01:32

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.
Types of Selection01:46

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...
Mate Choice01:20

Mate Choice

Mate choice—the decision about whom to mate with—is a type of natural selection, since animals must reproduce to pass down their genes. Mate choice is also called intersexual selection because the behavior occurs between the sexes.
Frequency-dependent Selection01:21

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.
X-linked Traits01:19

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
X-linked Traits01:19

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.

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Related Experiment Video

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Identification of Rare Antigen-Specific T Cells from Mouse Lungs with Peptide:Major Histocompatibility Complex Tetramers
09:15

Identification of Rare Antigen-Specific T Cells from Mouse Lungs with Peptide:Major Histocompatibility Complex Tetramers

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Sex-specific selection for MHC variability in Alpine chamois.

Helmut Schaschl1, Franz Suchentrunk, David L Morris

  • 1Department for Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Savoyenstrasse 1, 1160 Vienna, Austria. helmut.schaschl@univie.ac.at

BMC Evolutionary Biology
|February 17, 2012
PubMed
Summary

Male chamois with greater diversity in their immune genes (MHC class II DRB heterozygosity) survive longer. This suggests stronger selection on immune genes in males due to reproductive challenges and higher parasite loads.

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Area of Science:

  • Evolutionary biology
  • Immunogenetics
  • Wildlife ecology

Background:

  • Male mammals generally have shorter lifespans than females, potentially due to traits favoring reproduction over survival.
  • Males often exhibit higher parasite burdens, suggesting differential selection pressures on immune genes between sexes.
  • High variability in Major Histocompatibility Complex (MHC) genes is crucial for pathogen defense and individual longevity.

Purpose of the Study:

  • To investigate if MHC heterozygosity confers a survival advantage in male Alpine chamois compared to females.
  • To explore the relationship between MHC genetic diversity and longevity in a wild mammal population.

Main Methods:

  • Long-term study of free-living Alpine chamois (Rupicapra rupicapra).
  • Analysis of MHC class II DRB locus variation and background heterozygosity using microsatellite loci.
  • Correlation of genetic data with survival rates, considering age and reproductive status.

Main Results:

  • Male chamois heterozygous at the MHC class II DRB locus showed significantly longer survival (P = 0.022).
  • No significant survival benefit was observed for females based on MHC heterozygosity.
  • Reproductively active males had impaired survival due to earlier depletion of fat reserves, especially in areas with scabies, a severe parasitosis.

Conclusions:

  • Increased MHC class II DRB heterozygosity is linked to longer survival in male chamois, indicating a benefit for males.
  • Reproductive activity, winter energetics, and higher parasite loads likely increase the importance of MHC-mediated immunity in males.
  • These factors suggest stronger evolutionary selection pressures on MHC genes in males compared to females.