Conditional allogrooming in the herb-field mouse

Among members of the family Muridae, the herb-field mouse, Apodemus microps , is unique in that aggression is almost entirely lacking. This species, th erefore, is a model organism for experimental studies of social behavior wi thout the confounding influence of aggression. We used video surveillance c ameras to assess the importance of self-grooming and allogrooming in the so cial life of this species. Detailed analysis of individual behavioral seque nces using Markov chain methods revealed that self-grooming is a relatively stereotypic, sex-independent activity usually lasting about 8 s. Allogroom ing is conditional in the herb-field mouse, because it takes the form of a reciprocal strategy, with the differences between nonmatching bouts varying according to whether the initiator of allogrooming is male or female and w hether both interactants are of the same or opposite sex. Our analysis reve aled that the exchange of allogrooming bouts between individuals of the sam e sex is reciprocal, but that males allow females to "defect" more often th an vice versa, and males groomed females for longer than predicted by the d istribution of individual self-grooming bouts. In those species where the d emand for mating by males is far greater than that offered by females, in o ther words where females may select mates, asymmetry of allogrooming may pr ovide a mechanism for females to test the "suitability" of males for mating . It may also provide the means for males to stimulate females before matin g. Furthermore, allogrooming was the only sex-dependent behavior of the sev eral tested in our experiment. As such, we suggest that allogrooming is the predominant premating mechanism in this species.