The age at which a juvenile female reaches sexual maturity can be modulated by a variety of environmental and social factors. Experiments described in this thesis were designed to enhance the current understanding of the relationships among three variables that influence the onset of sexual maturation in female mice (Mus musculus), including:  exposure to dietary phytoestrogens during development,  variations in prenatal androgens, and  the presence or absence of genetically-unrelated males after weaning. For the first time, age at onset of male-induced female puberty was investigated using non-invasive behavioural and fertility measures. Through enzyme immunoassay procedures, daily output of urinary creatinine, 17P-estradiol, and progesterone was profiled in developing females that were either isolated or exposed to adult males. Uterine and ovarian tissue was also measured in such females, and male exposure was observed to increase reproductive tissue mass and was influenced by prior androgen exposure in interaction with diet and male presence. Male-exposed females fed a diet containing phytoestrogens immediately became sexually receptive when housed directly with males, and they conceived earlier than females in other conditions. Females with longer anogenital distance, which reflects higher in utero androgen exposure, displayed more escape attempts and aggressive posturing in the direct presence of males, especially when they had been housed near males and fed the phytoestrogen-containing diet. Urinary 17P-estradiol was substantially reduced in females raised on the phytoestrogenfree diet. Urinary output of progesterone was not strongly influenced by diet. Maleexposed females ' output of progesterone and 17P-estradiol was more dynamic in comparison to that of isolated females. The size of this effect depended on diet, prior androgen exposure, and whether urinary steroid measures were adjusted by urinary creatinine. Urinary creatinine was elevated by the low phytoestrogen diet and reduced by male exposure. These data suggest that dietary phytoestrogens and in utero androgen exposure interact with presence or absence of males in determining the age at onset of sexual maturity in developing females.
A final experiment was designed to examine two components of adult male urine, preputial gland emissions and unconjugated estrogens, that have been posited to act on females to advance reproductive maturation. Intact and preputialectomized males were compared in their output of urinary creatinine, 17~-estradiol, and testosterone, and in their influence on reproductive tissue in juvenile females. Lack of preputial glands did not hinder the capacity of males to induce uterine and ovarian growth in females. Male urinary creatinine was reduced by exposure to juvenile females. Creatinine-adjusted 17~estradiol and testosterone were greater in female-exposed males, regardless of whether the preputial glands were present. Based on these findings and those reported elsewhere, it is probable that male excreted urinary steroids are important in regulating reproductive changes in developing females exposed to males.