Chemical signals in male house mice urine: protein-bound molecules modulate interaction between sexes

The role of urinary chemosignals in sexual interactions was investigated in pairs of adult mice. Based on previous findings, volatile molecules bound by the Major Urinary Proteins (MUPs) from adult male urine were thought to be sufficient to carry information about the sex of the emitter, and thus sufficient to modify the behaviour of conspecifics. In the first experiment, virgin and stud adult males were exposed to receptive females painted or not with MUPs-borne molecules. Both virgin and stud males showed an increased latency to the first anogenital sniff and a reduced number of sniffings towards MUPs-treated females. This suggests that adult mice are repelled by MUPs-borne volatile molecules, even in the presence of female stimuli conveyed by receptive mates. In the second experiment only stud males were tested, with ovariectomized or estrogen-primed females. These latter were either untreated, painted with MUPs-borne molecules or MUPs without volatile ligands. Ovariectomized females and those treated with MUPs without ligands received less sniffs than the other two groups. Estrogen-primed females were mounted more times, with a shorter latency. Ovariectomized females and females treated with MUPs-borne ligands were attacked earlier by males. The presence of chemical cues from male urine is thus sufficient to modify the behaviour of stud males towards receptive females. In particular, MUPs-borne volatiles are sufficient to act as male cues and to induce aggression towards receptive females. It can be speculated that in nature adult male mice rely on olfactory cues like MUPs-borne odorants to firstly identify a male conspecific and possibly use similar chemical cues from their own urine to signal their presence.