Urine-derived key volatiles may signal genetic relatedness in male rats.

Olfactory cues play a vital role in kin recognition and mate choice of the rat. Here, using 2 inbred strains of rats, Brown Norway (BN) and Lewis, as models to simulate kinship via genetic distance, we examined whether urine-derived volatiles are genetically determined, and, if so, how they code for olfactory information and the degree of genetic relatedness in mate choice. Binary choice tests showed that BN females preferred the urine odor of Lewis males over that of BN males, suggesting that they avoided males genetically similar to themselves and were able to assess this olfactorily. Gas chromatography-mass spectrometry analysis revealed that the composition of urine-derived volatiles was more similar within strains than between strains and suggests that odortypes may reflect genetic relatedness. Our data further show that BN males had lower ratios of 2-heptanone and 4-heptanone and higher ratios of dimethyl sulfone and 4-ethyl phenol than Lewis males. When we supplemented BN and Lewis male urine to make each similar, the preferences of BN females were reversed. We conclude that some urine-derived volatiles covary in relative abundance with degree of genetic relatedness, and this relationship may play a key role in chemical signaling and genetic identity in this species.