Gonadectomy
To assess agonistic behavior in the absence of gonadal steroid hormones,we performed behavioral experiments in castrated males. Testes were removed through a small lateral incision as described for the basic surgery procedure. Postsurgical care was also performed as previously described. To ensure that levels of circulating steroids had declined,castrated males were used in behavioral dyadic encounters at least one month after surgery. Contests in GDX dyads (both castrated contenders) were compared to contests in SHAM dyads (both SHAM contenders). GDX and SHAM encounters were performed simultaneously.The success of gonad removalwas confirmed by quantification of plasma levels of 11-KT in GDX vs. SHAM individuals (see below).