Fertility and Mating Behaviour of Androgenized Mice

Abstract

Female Bagg mice injected with 1 mg testosterone propionate when 5 days old (androgenized mice) were sterile when they were mated at the age of 3 months. It was shown that the sterility was not due to a failure to ovulate but rather to aggressive behaviour towards the male which apparently prevented sexual consummation. The results of this study are compared with those of an earlier study (Peters & S\l=o/\rensen,1970) in which androgenized Bagg mice were mated immediately after weaning at the age of 1 month. These animals showed reduced fertility, but were not sterile. Fighting in this group of mice was only moderate and copulation and impregnation took place throughout maturity. The possible reasons for the different fertility and behaviour towards the male in androgenized mice that are mated at different ages are discussed. Androgenized females housed with males from the time of weaning, however, behave in a manner similar to that of mice which have been reared together: they fight rarely and then only moderately. It is thought that in androgenized mice a stimulus (probably a pheromone) activates their brain, previously programmed for aggression, when their first contact with a male is in adulthood: they do not become sensitive to the stimulus if they remain in constant contact with a male from the time they are weaned.Consequently, androgenized mice that are first mated when they are adult, fight their male mates, preventing insemination: those reared with a male accept and permit sexual contact when they are adult.

Variation in phenotype due to random intrauterine positioning of male and female fetuses in rodents

“…Examples of such sex-related characteristics are within-sex aggression (Beatty, 1979), urine marking of a novel environment (Bronson, 1976), copulatory behaviour (Beach, 1979;Södersten, 1979), infanticide or maternal behaviour towards young (Svare, 1979), and maternal (lactation-induced) aggression (Svare, 1980). In addition, the timing of puberty and length of oestrous cycles are markedly influenced by exposure to testosterone during both prenatal (Turner, 1939) and neonatal life (Peters & Sorensen, 1971). The following discussion will concern comparisons of these types of characteristics in OM and 2M females and males and the possible relevance of variation in these characteristics to the reproductive ecology of rodents.…”