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Related Concept Videos

Inclusive Fitness00:57

Inclusive Fitness

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Most altruistic behavior—in which one animal helps another at a cost to themselves—occurs between relatives. Scientists think these altruistic behaviors evolved because they increase the inclusive fitness of the animal providing help.
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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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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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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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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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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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The repeatable opportunity for selection differs between pre- and postcopulatory fitness components.

Lucas Marie-Orleach1,2,3,4, Nikolas Vellnow1,5, Lukas Schärer1

  • 1Department of Environmental Sciences, Zoological Institute University of Basel Basel 4051 Switzerland.

Evolution Letters
|February 8, 2021
PubMed
Summary

Postcopulatory sexual selection in flatworms is stronger than precopulatory selection. This study introduces a new method to measure repeatable selection, disentangling deterministic and stochastic components for a clearer understanding of sexual selection strength.

Keywords:
Cryptic female choicehermaphroditesmate choicemeasuring selectionopportunity for sexual selectionsperm competition

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Area of Science:

  • Evolutionary Biology
  • Sexual Selection
  • Reproductive Biology

Background:

  • Intense sexual selection can occur before and after copulation in multiply mating species.
  • Comparing pre- and postcopulatory selection is difficult due to challenges in observing postcopulatory events and the mixed components of the opportunity for selection metric.
  • The flatworm Macrostomum lignano, a simultaneously hermaphroditic species, provides a model for studying sexual selection.

Purpose of the Study:

  • To quantify pre- and postcopulatory male fitness components in Macrostomum lignano.
  • To develop and apply a novel method for assessing the repeatable opportunity for selection, disentangling deterministic and stochastic components.
  • To compare the strength of pre- and postcopulatory sexual selection in this species.

Main Methods:

  • Utilized fluorescent sperm-tracking transgenics for in vivo observation of postcopulatory processes.
  • Sequentially exposed focal worms to three mating groups to assess mating success, sperm-transfer efficiency, sperm fertilizing efficiency, and partner fecundity.
  • Calculated the repeatable opportunity for selection (I_R) by combining variance (I) and repeatability (R) of individual success.

Main Results:

  • Postcopulatory processes, specifically sperm-transfer and sperm-fertilizing efficiency, exhibited a higher repeatable opportunity for selection compared to mating success.
  • This indicates that postcopulatory sexual selection is stronger than precopulatory sexual selection in Macrostomum lignano.
  • The study successfully demonstrated that the opportunity for selection includes a repeatable, deterministic component.

Conclusions:

  • Postcopulatory sexual selection plays a more significant role than precopulatory selection in the studied flatworm species.
  • The developed method of calculating the repeatable opportunity for selection provides a more accurate estimation of selection strength.
  • This approach allows for the separation of deterministic and stochastic elements influencing selection, advancing the study of evolutionary processes.