Male social status, physiology, and ability to block pregnancies in female house mice (Mus musculus)

Abstract

1. Dominant and subordinate male house mice (Mus musculus) were examined for differences in ability to induce a pregnancy block (Bruce effect) in recently inseminated female conspecifics. 2. A male became behaviorally dominant or subordinate by one or two daily 15-min agonistic encounters with one other male for 5 months. Social status was monitored by the outcome of daily fighting, urine-marking patterns, and the ability of the animals' urine to increase uterine weights in prepubertal females. Clear differences were found in all these parameters during the experiments. When killed, dominant males had larger testes, preputials, and seminal vesicles. Adrenal glands were significantly heavier in subordinates. 3. Subordinates blocked pregnancies as effectively as both dominants and control males with no previous agonistic social experience.