We found that the order of aggressiveness of adult male Japanese quail determined by paired fighting was not correlated with plasma testosterone level, plasma LH level, size of cloacal protrusion, testicular weight, nor body weight. Injections of testosterone into lower-ranked individuals did not elevate their ranks of aggressiveness. Aggressive behavior was lost after castration. Injections of testosterone, androstenedione, and estradiol-17β restored aggressive behavior in castrated males. The order of aggressiveness of these hormone-injected castrated birds was identical to the order observed before castration. Administration of individually different doses of testosterone did not change the order. Injections with 5α- and 5β-dihydrotestosterone did not restore aggressive behavior in castrated males. These results are consistent with the hypothesis that aggressive behavior in adult male Japanese quail, as well as their sexual behavior, is induced by estradiol-17β converted by aromatase in the brain from testosterone. However, no correlation seems to exist between the endogenous or exogenous testosterone level and the order of aggressiveness.
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