The Function of Scentmarking in Spectral Tarsiers

Abstract

One of the primary trends characterizing primates as distinct from other mammals is their increasing dependence on vision and the concomitant reduced dependence on their sense of olfaction (Fleagle 1998; Martin 1990). Although most primates rely heavily on their sense of vision, their olfactory sense still plays an important role in their day to day activities (Charles-Dominique 1977; Harcourt 1981; Clark 1982; Epple et al. 1988; Dugmore and Evans 1990; Fornasieri and Roeder 1992; Harrington 1977). This is especially true of prosimian primates that have undergone the least reduction in their olfactory apparatus relative to the other primates (Martin 1990; Fleagle 1998). Prosimian primates are known to deposit scent around their territory. Two major hypotheses have been proposed to explain the function of scentmarking behavior in primates and other mammals. First, it has been hypothesized that scentmarking serves to mark off territorial boundaries. For example, in Lemur catta, the majority of the scent marks were in a narrow band within the area of overlap that coincided with the positions of inter-troop confrontations (Mertl-Millhollen 1988). Scentmarks in Lemur catta thus appear to demarcate territorial boundaries and not the completed home range boundaries. This hypothesis has also been proposed for a variety of other animals including pronghorn antelope (Gilbert 1973), hyenas (Gorman 1990), oribi (Gosling 1981), African dwarf mongoose (Rasa 1973), aardwolf (Richardson 1990), and European badger (Roper et al. 1986). It has also been proposed that scentmarking enables group members to monitor female reproductive condition, thereby serving a mate defense function. Male cotton-top tamarins Saguinus oedipus are capable of discerning the chemical signals of ovulation as are meadow voles (Ferkin et al. 1995; Ziegler et al. 1993). This hypothesis has been proposed to account for the ability of males to locate sexually receptive females in many of the nocturnal solitary foraging prosimians (Charles-Dominique et al. 1980; Doyle and Martin 1979; Tattersall and Sussman 1977). Spectral tarsiers have a number of scent marking glands that they use to deposit scent throughout their range. These include (1) the ano-genital gland, (2) the epigastric gland, and (3) the circum-oral gland (Niemitz 1984). They are also known to scentmark by depositing small droplets of urine on substrates. Although previous studies have described the form of scent marking behavior in semi-wild (caged in their natural habitat) (Niemitz 1984), and wild spectral tarsiers (MacKinnon and MacKinnon 1980), no quantitative attempts have been made to identify the function of this behavior. If the function of spectral tarsier scent marking is to communicate information about the female’s reproductive condition, then it is predicted that (1) scentmarks will be randomly distributed throughout the territory and not restricted to the territorial borders and (2) scentmark frequency will increase during the mating season compared to the nonmating season. If spectral tarsier scentmark in order to defend their territory, then it is predicted that (1) both males and females will scentmark equally; (2) scentmarks will not be randomly distributed throughout the group’s territory, but will be restricted to the territory borders, particularly at the areas of overlap; and (3) scent marking behavior will increase in frequency during territorial disputes.