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Related Experiment Videos

Testosterone and aggression: Berthold, birds and beyond.

K K Soma1

  • 1Department of Psychology, Graduate Program in Neuroscience, and Brain Research Centre, University of British Columbia, Vancouver, BC, Canada. ksoma@psych.ubc.ca

Journal of Neuroendocrinology
|June 16, 2006
PubMed
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Testosterone influences aggression in song sparrows, but aggression can also raise testosterone levels. Nonbreeding sparrows remain aggressive even without testosterone, suggesting alternative brain mechanisms regulate this behavior.

Area of Science:

  • Neuroendocrinology
  • Behavioral Ecology
  • Animal Behavior

Background:

  • Berthold's 1849 study established testicular secretions' role in aggressive behavior.
  • Wild songbird studies reveal complexities and limitations to early hypotheses.
  • Aggression and testosterone levels exhibit a bidirectional relationship in breeding song sparrows.

Purpose of the Study:

  • To investigate the neuroendocrine control of aggression in nonbreeding song sparrows.
  • To explore alternative mechanisms regulating aggression beyond circulating testosterone.
  • To examine the role of oestradiol and its synthesis pathways in aggression.

Main Methods:

  • Field studies on North American song sparrows (Melospiza melodia).
  • Observation of aggression levels and plasma testosterone during breeding and nonbreeding seasons.

Related Experiment Videos

  • Administration of fadrozole (aromatase inhibitor) and oestradiol in nonbreeding males.
  • Investigation of dehydroepiandrosterone (DHEA) metabolism and central oestradiol synthesis.

    • Main Results:

    • Nonbreeding song sparrows exhibit high aggression despite low plasma testosterone.
    • Castration does not reduce aggression in nonbreeding males.
    • Fadrozole significantly decreases nonbreeding male aggression, reversible with oestradiol.
    • Evidence suggests peripheral DHEA or central de novo synthesis of oestradiol regulates aggression.

    Conclusions:

    • Aggression in nonbreeding song sparrows is regulated by brain oestradiol, not circulating testosterone.
    • Central oestradiol synthesis may bypass the costs of circulating testosterone in the nonbreeding season.
    • These neuroendocrine mechanisms are likely conserved across diverse vertebrate species.