Long-Term Effect of a Urinary Chemosignal on Reproductive Fitness in Female Mice

The effect of synthetic 2,5-dimethylpyrazine (a compound naturally produced by grouped females) on the overall reproductive success of female mice was investigated. The exposure of tested females to control or experimental stimuli began on the day of birth and lasted throughout maturation, mating, pregnancy, and the lactating of their first litters. Females exposed to this urinary compound attained their first estrus significantly later than the animals exposed to water only. On average, the prepubertal, exposed females reached puberty 3.7 to 3.9 days later than the unexposed animals. The females in which puberty was delayed by this synthetic chemosignal did not show a single fully completed estrous cycle before the age of 35 days. Only 52-64% of exposed females successfully bred and reared their litters as compared to 86-96% of the unexposed, control females (p < 0.05). A significantly higher mortality of pups associated with 2,5-dimethylpyrazine exposure during lactation was observed. The reproductive deficit displayed by females born into a 2,5-dimethylpyrazine environment is qualitatively similar to the effect observed in dense populations, in both laboratory and free-living conditions.