Hormonal Control of Aggressive Behavior in Japanese Quail

Abstract

Abstract1. Thirty-four five-month old male Coturnix were divided into 17 pairs on the basis of matched body weights (mean difference within pairs = 2 grams). The members of each pair were separated except during daily five-minute pair encounters. 2. Two classes of response were measured during the encounters: "head-grabs" and "pecks". A bird was called dominant if he performed more head-grabs and pecks than his pair-mate during the last three of four preexperimental encounters. 3. After the first four encounters the 17 pairs were divided into four groups: castrate, in which the dominant birds underwent bilateral gonadectomy (five pairs); sham operate, in which the dominant birds underwent the surgical procedure of the castrate group except for testis removal (four pairs) ; TCP injected, in which the submissive birds were administered testosterone cyclopentypropionate on a regular schedule (four pairs) ; and saline injected, in which the submissive birds were administered saline on the same schedule (four pairs). Pairs were observed for 23 encounters subsequent to the first experimental manipulations. 4. Gonadectomy had a clear, rapid effect on the behavior measured. From the fourth postoperative encounter through the eleventh, the (originally dominant) castrated birds performed zero head-grabs and zero pecks. The behavior of the pair-mates increased sharply during this time. 5. From the eleventh through the twenty-third postoperative encounter the castrated birds were given four injections of TCP. Androgen injections led to the reestablishment of original dominance relations in all cases. 6. Sham operations produced a mild effect on the established dominance relations. The operated animals showed relatively slight decreases in head-grabs and pecks; some pair-mates showed increased peck frequencies. In contrast to the behavior of the castrates, zero responding by the sham operates was rare. 7. TCP injections produced large changes in the behavior of three out of four intact submissive birds, and a slight change in the fourth. Androgen increased the average number of headgrabs and pecks exhibited by the injected animals by a factor of more than four; the pair-mates showed substantially reduced rates of responding (encounters 6-9). Cessation of androgen treatment produced a reversion to original relations within nine encounters after the last injection. 8. Treatment with saline had no effect on the originally established dominance relations. 9. The level of aggressive activity could be manipulated by varying the level of circulating androgen. Analysis of the functional significance of the observed behavior was made difficult by the close similarity of response in these homosexual contacts to that observed during heterosexual contact.