Sexual Development of Female Prairie Deermice: Influence of Physical versus Urine Contact with Grouped or Isolated Adult Females

Female prairie deermice (Peromyscus maniculatus bairdii) born into freely growing laboratory populations are drastically retarded in sexual development. The reproductive organs of these animals are significantly smaller than those of controls maintained as bisexual pairs (Terman, 1969, 1973b, 1979, 1980). For example, the uteri and ovaries of population females range from 0.20 to 0.33 the size of those of controls. Pairing of these reproductively-retarded animals with proven mates is followed by reproduction in approximately 50% of the mice within 40 days (Terman, 1973a). These data suggest that the retarding mechanism is reversible and is a socially related phenomenon. Recent studies have demonstrated the influence of tactile cues on sexual development. Young born into populations and reared as bisexual pairs in cages in which they received visual, auditory, or olfactory but not tactile stimulation from population animals developed significantly larger reproductive organs than their sibs freely ranging in the populations (Terman, 1979). More recent work in the same context but with older animals has shown that once the reproductive organs were retarded in development, other cues (auditory, visual, olfactory) may act to slow the growth recovery of these organs in animals housed in cages within the population enclosures (Terman, 1980). The present experiments were designed to explore further the influence of olfactory and tactile cues on sexual maturation in young prairie deermice. Specifically, the purpose of these experiments was to test the influence of contact with adult females, their urine or distilled water on sexual development to 40 days of age as measured by the ovarian and uterine weights of young female prairie deermice. Three experiments were conducted sequentially. In each, young females 21-24 days of age born into a laboratory colony were weighed, marked by toe clipping and placed in contact with one or more adult females, their urine, or distilled water. The young females were treated as follows: Experiment 1-in contact with one or two adult females, their urine or distilled water; Experiment 2-in contact with four adult females, their urine or distilled water; Experiment 3-in contact with eight adult females, their urine or distilled water. Adult (95-150 days of age) nulliparous females were the source of the urine used in this experiment. The adult females were maintained alone or in groups of two, four, or eight unrelated females in a single chamber of a two compartment opaque plastic cage. Insofar as possible, when a young female was placed with adults, a sister was placed in the adjacent chamber of the two-chambered cage, and another sister was isolated in a single chamber of a separate cage. Urine was collected every other day by placing individual adult females in a funnel apparatus consisting of a 200-ml glass jar with a screen top inverted within a polypropylene funnel for a 3to 4-h period. Urine from each donor group was pooled, kept separate from other donor groups, stored in a refrigerator, and used no more than 2 days after collection. The appropriate urine or distilled water was applied daily to a circular area approximately 3 cm in diameter on the inside front corner of the cage of each isolated animal. The urine of a donor or a group of donors was applied in the adjacent chamber of the cage where the donors were housed. Application was by three strokes of a #2 artist's brush freshly dipped in the appropriate solution. Control animals were kept in isolation and distilled water was painted in their cages daily. At 40 days of age, the young females were killed with chloroform, weighed, the visceral cavity was opened, and the entire animal was placed in 10% buffered formalin. The ovaries and uteri were cleaned of fat, lightly blotted, and weighed to the nearest 0.01 mg. Multiple comparisons of the treatment means of the body, ovarian, and uterine weights in each experiment were made by Duncan's New Multiple Range Test at P < 0.05. The mean weights and standard errors of the body, ovaries, and uteri of the experimental females in experiments one, two and three are presented in Table 1. The body weights of females in each of the three experiments did not differ significantly across treatments. 504 Vol. 65, No. 3