Extra-gonadal steroids modulate non-breeding territorial aggression in weakly electric fish

Area of Science:

• Neuroendocrinology
• Animal Behavior
• Fish Biology

Background:

• Intraspecific aggression is regulated by neuroendocrine factors, with androgens often linked to reproductive aggression.
• Aggression can occur in non-breeding seasons when gonads are regressed and steroid hormone levels are low.
• In mammals and birds, aromatization of androgens to estrogens is crucial for aggression regulation year-round.

Purpose of the Study:

• This study investigates the role of steroids in modulating non-breeding aggression in the teleost fish, Gymnotus omarorum.
• It is the first study to explore steroid modulation of non-breeding aggression in teleost fish.
• The research examines the relationship between 11-Ketotestosterone (11-KT) levels, aggression, aromatization, and gonadal steroid sources in G. omarorum.

Main Methods:

• Analyzed male-male non-breeding agonistic behavior in G. omarorum.
• Compared circulating 11-Ketotestosterone (11-KT) levels between dominant and isolated males.
• Assessed the role of aromatase inhibition and evaluated gonads as a steroid source, including castration experiments.

Main Results:

• High levels of aggression were observed in the non-breeding season despite low plasma 11-KT levels.
• No significant difference in 11-KT levels was found between dominant and isolated males.
• Aromatase inhibition reduced aggression and altered contest dynamics, while castration did not affect aggressive behavior.

Conclusions:

• Non-breeding territorial aggression in G. omarorum is independent of circulating 11-KT levels.
• The study demonstrates that aggression in this species during the non-breeding season relies on a non-gonadal estrogenic pathway.
• This finding highlights a novel mechanism for aggression regulation in teleost fish.