ORIGINAL PAPER Dietary protein content affects the response of meadow voles, Microtus pennsylvanicus, to over-marks Nicholas J. Hobbs & Michael H. Ferkin Received: 4 June 2010 / Revised: 21 December 2010 / Accepted: 10 January 2011 / Published online: 26 January 2011 # Springer-Verlag and ISPA 2011 Abstract The response to signals, including scent marks, from opposite-sex conspecifics can be affected by the nutritional state of both the sender and receiver of these signals. Protein content of the diet affects how meadow voles (Microtus pennsylvanicus) respond to single scent marks, but it is unknown how it affects an individual’s response to the overlapping scent marks of two donors (an over-mark). In experiment 1, we tested the hypothesis that protein content of the diet affects the amount of time voles spend investigating the marks of the top- and bottom-scent donors of an over-mark. Males and females fed a 22% protein diet spent more time investigating the scent mark of the top-scent donor than that of the bottom-scent donor; voles fed 9% and 13% protein diets spent similar amounts of time investigating the top- and bottom-scent donors. In experiment 2, we tested the hypothesis that protein content of the diet of the top- and bottom-scent donors affects the amount of time conspecifics spend investigating their scent marks. Female voles spent more time investigating the mark of the top-scent male than that of the bottom-scent male, independent of the differences in protein content of the diets of the top- and bottom-scent donors. Male voles, however, spent more time investigating the top-scent female when she was fed a diet higher in protein content than that of the bottom-scent female. Our results are discussed within the context of the natural history of voles. Keywords Over-mark . Meadow vole . Communication . Dietary protein Introduction Communication between opposite-sex conspecifics can be affected by the nutritional state of those participating. For example, in many species individuals that have been food- deprived or fed a low-protein diet are less responsive to signals from opposite-sex conspecifics than are individuals that are well-fed or fed a high protein diet (Louis et al. 1994; Hunt et al. 2005; Pierce et al. 2005a,b; 2007a). Thus, the diet and subsequent quality of the receiver affect how it responds to the signals of opposite-sex conspecifics (Ferkin et al. 1997; Fisher and Rosenthal 2006; Hobbs et al. 2008). In addition, the diet and subsequent quality of the sender affect how opposite-sex conspecifics respond to its signals (Wade and Schneider 1992; Ferkin et al. 1997; Gill and Rissman 1997; Jones and Wade 2002; Pierce et al. 2007b; Hobbs et al. 2008). In many species, traits used by males to attract or indicate interest in females are influenced by dietary components such as dietary protein (Ferkin et al. 1997; Droney 1998; McGlothlin et al. 2007; Hobbs et al. 2008), calcium (McGraw 2007), vitamin D (Martin and Lopez 2006), and carotenoids (Kodric-Brown 1985; Hill 1991, 1992), with females responding preferentially to males fed diets high in these substances. Thus, a male’s nutritional state may be an accurate indicator of his relative quality (Kodric- Brown and Brown 1984; Roberts 2007). By selecting males in a better nutritional state, females may accrue indirect and direct benefits, which would increase her reproductive success (Zeh and Zeh 1988; Grafen 1990; Johnstone 1995). For many terrestrial mammals, information about their nutritional state can be conveyed via their scent marks N. J. Hobbs : M. H. Ferkin Department of Biological Sciences, The University of Memphis, Ellington Hall, Memphis, TN 38152, USA N. J. Hobbs (*) 3700 Walker Ave., Memphis, TN 38152, USA e-mail: nhobbs@memphis.edu acta ethol (2011) 14:57–64 DOI 10.1007/s10211-011-0090-0