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Static allometry and animal genitalia.

William G Eberhard1

  • 1Smithsonian Tropical Research Institute, and Escuela de Biología, Universidad de Costa Rica, Ciudad Universitaria, Costa Rica. william.eberhard@gmail.com

Evolution; International Journal of Organic Evolution
|September 23, 2008
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Summary

Male genitalia in arthropods and vertebrates show a trend for low static allometric values, differing from other sexually selected traits. This suggests a broader evolutionary explanation beyond just female choice.

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Area of Science:

  • Evolutionary biology
  • Comparative anatomy
  • Sexual selection

Background:

  • Sexual selection often drives the evolution of exaggerated traits, typically showing steep allometric slopes.
  • Genital morphology is crucial for reproductive success but its allometry is less understood.
  • Previous explanations for genital allometry focused solely on female choice.

Purpose of the Study:

  • To investigate the allometric trends of male genitalia across diverse species.
  • To compare genital allometry with other sexually selected traits.
  • To propose a more comprehensive explanation for the observed allometric patterns in genitalia.

Main Methods:

  • Surveyed 117 arthropod species and 17 vertebrate species.
  • Analyzed static allometric values of male genitalia.
  • Compared genital allometry with other structures under sexual selection.

Main Results:

  • A strong trend for low static allometric values was observed in male genitalia across surveyed species.
  • This trend contrasts with the typically steep allometric slopes of other sexually selected structures.
  • The trend was less consistent in mammals compared to arthropods.
  • Preliminary data on female arthropod genitalia suggest similar low allometric slopes.

Conclusions:

  • The "one-size-fits-all" explanation for low genital allometric slopes needs revision.
  • A more general model incorporating both natural and sexual selection, including mechanical fit and stimulation, is proposed.
  • This broader model may also explain the allometry of female genitalia in arthropods.