Lack of changes in the courtship behaviour of male ring doves after testosterone treatment

The courtship behaviour of male birds depends on gonadal androgen. To date, however, there is little evidence that the expression and the features of courtship behaviours are proportional to the concentration of circulating androgen. The existence of such dose-dependent relationship is at the basis of several current theories of sexual selection. In the male ring dove (Streptopelia risoria) gonadal testosterone (T) controls courtship displays either directly (aggressive displays, i.e. bowing and chasing) or after conversion into oestradiol within the brain (nest-oriented displays). We studied whether the treatment of intact, sexually active males with T induces short-term changes in the fine structure of the bowing display and in the frequency of the courtship displays. Because nest-soliciting depends on brain oestrogen formation, we also measured the activity of the oestrogen-synthesising enzyme aromatase in the brain areas controlling courtship. The structure of the bowing display and the pattern of the courtship were not affected by either of two T treatments that elevated circulating androgen within the physiological range. Males implanted with the higher dose of T had higher aromatase activity in the anterior hypothalamus. Our results indicate that T modulates brain aromatase in intact males and suggest a threshold model of action of steroid hormones on the structure of courtship behaviour.