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4. Scent Marking
- Johns Hopkins University Press
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FOUR Scent Marking After the error of atheism, there is nothing that leads weak minds further astray from the paths of virtue than the idea that the minds of other animals resemble our own, and that therefore we have no greater right to future life than have gnats and ants. René Descartes, Passions of the Soul, 1649 In this chapter the influences of learning will be shown to be particularly salient in responses to conspecific scent marks or depositions commonly said to contain pheromones, emphasizing the fact that invariant responses to chemical stimuli are not the norm in mammals. Scent marking is one of the most common socially related behaviors of mammals. As a sexually dimorphic trait, species-specific behaviors used in scent marking, such as the leg lift urination posture of the dog, depend in large part upon intrauterine exposure of the brain to testosterone, sensitizing neural structures to activation by testosterone in adulthood (Beach, 1974) (Figure 4.1). Scent marking is present within at least 15 of the 18 mammalian orders and within the entire range of social structures (e.g., pair-bonded territories; single-male territories, or demes, with clearly de- fined boundaries; single-male territories around harems, packs, etc.) and is a critical means by which many macrosmatic mammals provide information regarding their location and physiological status. In most species, males do the majority of the marking and, when scent glands are involved , have larger scent glands than females (Figure 4.2). This behavioral and structural sexual dimorphism appears analogous to that of many birds. Thus, just as the males of most avian species are brightly colored and are more involved in territorial and courtship displays than 47 48 THE GREAT PHEROMONE MY TH the females, most male mammals are more brightly odored, if you will, and more involved in territorial scent-marking activities (Doty, 1974). Like the individual plumage of birds or the characteristics of human faces, the scent sources of mammals are complex. The components of scent glands and urine, for example, can number in the hundreds and even thousands, depending upon such non-mutually exclusive factors as genetics, commensal bacteria, season, habitat, diet, housing conditions, and endocrine state (Schellinck and Brown, 1999; Pohorecky et al., 2008). In the case of urine, Rasmussen and Krishnamurthy (2000) state: The number and complexity of chemical compounds in urine is enormous— up to several thousand different compounds. Large volumes of emitted urine may remain in liquid form for several days. Thus, urine represents a relatively persistent signal. In addition, compounds or blends impart difSTAND FLEX LEAN RAISE ELEVATE HANDSTAND FLEX-RAISE LEAN-RAISE SQUAT ARCH SQUAT-RAISE ARCH-RAISE FIGURE 4.1 Twelve elimination postures observed in purebred beagles. In 60 males and 53 females tested, males predominantly urinated using the elevate posture (97%) and the raise posture (2.1%). Females used a wider range of postures, including the squat (68%), the squat raise (19.3%), the raise (4.6%), and the flex-raise (3.1%). Modified from Sprague and Anisko (1973); used with permission of Koninklijke BRILL NV. [54.210.126.232] Project MUSE (2024-03-29 03:04 GMT) SCENT MARKING 49 ferent messages, and various compounds degrade at different rates, providing a temporal indication of signal age and thus the presence of the emitter... The presence of proteins may retard this degradation or affect the release rate of smaller, more volatile compounds. (p. 408) The influence of diet on the attractiveness of urine or scent marks has been demonstrated in a range of species, including guinea pigs (Beauchamp , 1976), meadow voles (Grigoriadis et al., 1989), and beavers (Tang et al., 1995). For example, meadow voles are more strongly attracted to scent marks of conspecifics having higher-protein diets (Grigoriadis et al., 1989), and many of the large number of phenolics and terpines found in the castoreum of beavers are diet-derived, conceivably advertising to potential mates the nutritional status of the individual and, indirectly, the food supply in his territory (Tang et al., 1995). Dietary factors can mask MSA MSA FIGURE 4.2. A. Shaven belly of male deer mouse (Peromyscus maniculatus bardaii) exposing the large midventral sebaceous scent gland area (MSA). B. Same area of female deer mouse showing much smaller scent gland region. Modified from Doty and Kart (1972). 50 THE GREAT PHEROMONE MY TH individual odors that may have a strong genetic determinant (Shellinck et al., 1997) and microbial products often produce the characteristic...