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How to Create and Use Binocular Rivalry
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Sibling rivalry: Males with more brothers develop larger testes.

Heidi S Fisher1,2, Kristin A Hook1, W David Weber1

  • 1Department of Biology University of Maryland College Park Maryland.

Ecology and Evolution
|September 26, 2018
PubMed
Summary

Male deer mice retain larger testes even in monogamy, suggesting evolutionary adaptations in sperm production persist. Early life competition, like having more brothers, also increases testis size and fertility.

Keywords:
deer mouseoffspring sex ratiophenotypic plasticitysexual selectionsperm competition

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Area of Science:

  • Evolutionary biology
  • Reproductive biology
  • Behavioral ecology

Background:

  • Paternity in promiscuous species is often determined by sperm competition.
  • Testis size correlates with gamete production and mating competition risk.
  • Deer mice (Peromyscus maniculatus) exhibit promiscuity, unlike monogamous sister species (P. polionotus).

Purpose of the Study:

  • To investigate the persistence of larger testes in promiscuous species under enforced monogamy.
  • To examine the influence of early rearing environment on adult testis size and fertility.

Main Methods:

  • Studied testis size in Peromyscus maniculatus after long-term enforced monogamy.
  • Utilized a second-generation hybrid population to assess environmental effects.
  • Correlated testis size with adult fertility.

Main Results:

  • Larger testes in P. maniculatus were maintained despite enforced monogamy.
  • Males reared with more brothers developed larger adult testes.
  • Increased testis size was associated with higher fertility.

Conclusions:

  • Evolutionary differences in sperm production can be stable across generations and environments.
  • Early developmental environment significantly impacts testis size and reproductive potential.
  • Sperm production is shaped by both long-term natural selection and early-life factors.