THE SECONDARY SEX CHARACTERS AND REPRODUCTIVE BEHAVIOR OF GONADECTOMIZED STICKLEBACKS TREATED WITH METHYL TESTOSTERONE

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Abstract
Treatment of intact juvenile or gonadectomized adult male and female stickle-backs with methyl testosterone, either by immersion in dilute solutions or by implantation of pellets into the body cavity, induces male secondary sex characters. The effect, as quantified by measurements of the height of the brush border tubules in the mesonephros, is the same in both sexes and reaches a maximum in 3 to 4 weeks. Both the gonadectomized males and females develop prespawning aggressive and territorial behavior if maintained 4 or 5 weeks under long-day photoperiods (16-hour day alternating with 8-hour darkness). Such behavior does not appear under a short photoperiod. The administration of methyl testosterone does not intensify aggressive behavior in either the 8-hour or 16-hour photoperiod fish. The combined effects of long photoperiods and methyl testosterone induces nest-building behavior (characteristic of normal breeding males) in 50% to 60% of the castrated males and about 6% of the gonadectomized females. The behavior of the treated males is qualitatively and quantitatively similar to naturally matured fish but that of the females shows differences. Although male sexual behavior may also be induced in androgen treated castrates it has not been observed in the females under comparable experimental procedures.