We investigated the relationship between aggression, plasma testosterone level (T), and change in T in captive male red jungle fowl (Gallus gallus). T measured on day 1 of our experiment was positively correlated with T on day 8, suggesting that T remains constant in males when the social environment is stable. During aggressive encounters that escalated to include physical combat, males that attacked first (won) had increased T relative to their opponent. Males did not differ in T measured 1 week before the aggressive encounter. Our data suggest that an increase in T during aggression is associated with winning in escalated fights.
Bibliographical noteFunding Information:
We thank Nigella Hillgarth, Margaret Kaufhold, Cassandra Hayes, Troy MacLarty, Joe Decruy-enaere, Christopher Janus, and Craig Dinger for help in carrying out this experiment. We thank Carl Ware for the use of his lab to do our radioimmunoassays. Finally, we thank two anonymous reviewers for constructive comments on our manuscript. This study was supported by NSF Grants DEB 9257749 and IBN 9120902 to Marlene Zuk.