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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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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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In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
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Natural Selection and Mating Preferences01:06

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The principle of natural selection posits that organisms better adapted to their environment are more likely to survive and reproduce. This principle is closely intertwined with mating preferences, a key aspect of sexual selection, which evolutionary psychologists believe is driven by instincts to propagate one's genes. Such instincts significantly influence mating behaviors and preferences between genders.
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Mate Choice01:20

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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.
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A complete procedure for testing a claim about a population proportion is provided here.
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Assessing Differences in Sperm Competitive Ability in Drosophila
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STABILIZING SELECTION AND VARIANCE IN FIG WASP SEX RATIOS.

S A West1,2, E A Herre1

  • 1Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama.

Evolution; International Journal of Organic Evolution
|June 2, 2017
PubMed
Summary
This summary is machine-generated.

Phenotypic variance in fig wasp offspring sex ratios is lower when single foundress broods occur more frequently. This supports the theory that traits under stabilizing selection show less variance as their fitness impact increases.

Keywords:
Fig waspsintensity of selectionsex ratiostabilizing selectionvariance

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Area of Science:

  • Evolutionary Biology
  • Behavioral Ecology
  • Population Genetics

Background:

  • Theoretical models predict a negative correlation between phenotypic variance of a trait and its fitness impact under stabilizing selection.
  • This relationship has been infrequently tested empirically, particularly in natural populations.
  • Pollinating fig wasp foundress offspring sex ratios are a model trait for studying stabilizing selection due to fitness consequences of extreme ratios.

Purpose of the Study:

  • To empirically test the theoretical prediction of a negative correlation between phenotypic variance and fitness impact for single foundress sex ratios.
  • To investigate if the frequency of single foundress broods influences the intensity of stabilizing selection on sex ratios.
  • To examine this relationship across multiple species of pollinating fig wasps.

Main Methods:

  • Studied 16 species of Panamanian pollinating fig wasps.
  • Quantified the phenotypic variance in single foundress sex ratios for each species.
  • Assessed the natural frequency of single foundress brood production per species.
  • Performed comparative analyses using species as independent data points and accounting for phylogenetic relationships.

Main Results:

  • A significant negative correlation was found between the phenotypic variance of single foundress sex ratios and the frequency of encountering single foundress broods.
  • Species with more frequent single foundress broods exhibited lower phenotypic variance in their sex ratios.
  • Phylogenetic comparative analysis confirmed the results obtained using species as independent data points.

Conclusions:

  • The findings support the theory that phenotypic variance decreases as the fitness impact of a trait under stabilizing selection increases.
  • The frequency of encountering single foundress broods acts as a proxy for the intensity of stabilizing selection on sex ratios in these wasps.
  • This study provides strong empirical evidence for the relationship between selection intensity and phenotypic variance in a natural system.