Self-Grooming Response of Meadow Voles to the Odor of Opposite-Sex Conspecifics in Relation to the Dietary Protein Content of Both Sexes Nicholas J. Hobbs, Allen M. Aven & Michael H. Ferkin Biology Department, The University of Memphis, Memphis, TN, USA Introduction Scent-marking (Johnston 1983, 2003; Gosling & Roberts 2001; Roberts 2007) and self-grooming (Thi- essen 1977; Thiessen & Harriman 1986; Ferkin et al. 1996) can signal interest in the opposite sex for many mammals. Self-grooming spreads odiferous substances that increase the active space of the odor field that surrounds groomers (Bossert & Wilson 1963), making them more easily detected by nearby opposite-sex conspecifics (Ferkin & Leonard 2005). Self-grooming may transmit information about the groomer that affects interactions with opposite-sex conspecifics (Steiner 1973, 1974; Brockie 1976; Thi- essen 1977; Gosling 1985; Thiessen & Harriman 1986; Witt et al. 1988; Ferkin et al. 2001; Ferkin 2006; Ferkin & Leonard, in press). For example, meadow voles spend more time self-grooming in response to odors of opposite-sex conspecifics in heightened states of sexual receptivity than those not in such states (Ferkin et al. 1996). Voles also spend more time self-grooming when exposed to odors of unfamiliar, opposite-sex conspecifics than to those of their opposite-sex siblings (Paz-y-Min ˜ o et al. Correspondence Nicholas J. Hobbs, Biology Department, The University of Memphis, Ellington Hall, Memphis, TN 38152, USA. E-mail: nhobbs@memphis.edu Received: April 11, 2008 Initial acceptance: May 24, 2008 Final acceptance: July 28, 2008 (S. A. Foster) doi: 10.1111/j.1439-0310.2008.01573.x Abstract Many animals self-groom when they encounter the scent marks of opposite-sex conspecifics. Self-grooming transmits odiferous substances that contain information about the groomer’s condition, which is affected by its nutritional state. We tested the hypothesis that the amount of time that individuals self-groom to opposite-sex conspecifics is affected by the amount of protein in their diet and that of the scent donor. We did so by feeding meadow voles (Microtus pennsylvanicus)a diet containing 9%, 13%, or 22% dietary protein for 30 d and observing their self-grooming behavior when they were exposed to bedding scented by an opposite-sex conspecific (odor donor) fed one of the three diets, or fresh cotton bedding (control). The hypothesis was partially supported. We found that the protein content of the diet of male and female groomers did not affect the amount of time they self-groomed. However, the protein content of the diet of male odor donors affected the amount of time that female voles spent self-grooming. Female voles self-groomed more in response to male odor donors fed a 22% protein- content diet than to those produced by male odor donors fed either a 9% or a 13% protein-content diet. Interestingly, the amount of time males self-groomed was not affected by the protein content of the diet of the female odor donor. These results may, in part, be explained by the natural history of free-living meadow voles, sex differences in costs associated with mate attraction and reproduction, and the direct or indi- rect benefits that females receive from males fed a diet high in protein content. Ethology Ethology 114 (2008) 1210–1217 ª 2008 The Authors 1210 Journal compilation ª 2008 Blackwell Verlag, Berlin