Influence of social dominance and female odor on the sperm activity of male mice

In mammals, sperm activity is known to be varied largely according to individuals though physiological reasons have not been clarified yet. In our previous study [Koyama S, Kamimura S. Lowered sperm motility in mice of subordinate social status. Physiol Behav 1999;65:665-669.], we showed that sperm motility was higher in the dominant mice than the subordinate mice, by which it was suggested that social factors could affect sperm activity in mammals. In the present study, we investigated how the observed influence of social dominance would be modified by the existence of females. From 5 to 15 weeks of age, male mice were pair housed and were kept under three different housing conditions: (1) with females; (2) with bedding soiled by females; and (3) control group. The social dominance of the paired males was determined by resident-intruder tests that were carried out from 8 to 15 weeks of age. At the end of 15 weeks of age, sperm activity, weights of organs, level of serum testosterone and corticosterone were determined. It was revealed that sperm density was higher and weight of preputial glands was heavier in dominants than in subordinates when they were kept with females or female bedding, In the subordinates, however, there were no differences among the three housing conditions; that is, there were no female effects on the subordinates. On the other hand, sperm motility was high in the dominants of control group, low in the subordinates, and lower in the dominants that were kept with females. The dominants of the males that were kept with females showed high aggressiveness, and there were negative correlationships to be seen between aggressiveness and sperm motility. It was suggested that: (1) Female odor promotes spermatogenesis of the dominants, but it does not promote that of the subordinates. (2) Sperm motility is more affected by social dominance than by female odor. (3) Excessive aggressiveness has negative influence on sperm motility. (C) 2000 Elsevier Science Inc. All rights reserved.