Changes in Plasma Testosterone and Aggressive Behavior in Male Green Iguanas (Iguana iguana) Following Orchidectomy

Abstract Eighteen green iguanas (Iguana iguana) were randomly assigned to three groups: control group (sham orchidectomy); group I (orchidectomy before the breeding season); and group II (orchidectomy during the breeding season). Circulating testosterone concentrations were determined using a radioimmunoassay and correlated with aggressive behavior scores. Monthly mean (± SD) testosterone concentrations and aggression scores varied with group and season. The highest testosterone concentrations were present in the control group (mean ± SD: 11.6 ± 2.8) during the breeding season (November through January). Likewise, the highest aggression scores were present in the control group (11.6 ± 9.6) and group II animals (4.7 ± 2.2) during the breeding season (November through January). Elevations in testosterone concentration preceded initial increases in aggressive behavior by approximately 1 month. Orchidectomy significantly decreased plasma testosterone concentrations between groups, with significant differences...