Alarm calling in yellow-bellied marmots: II. The importance of direct fitness

Alarm calling in sciurid rodents is often explained by inclusive fitness benefits that callers accrue. Inclusive fitness arguments imply that indirect fitness plays an important role in the evolution and maintenance of alarm calling. A more parsimonious hypothesis is that animals alarm call to increase their direct fitness by warning their offspring. Group-living animals are related to each other social group member by a coefficient of relatedness, r, that theoretically ranges from 0–1.0. The sum of these pair-wise coefficients, ‘total r’, reflects the magnitude of possible inclusive fitness benefits. The amount of variation in the rate of yellow-bellied marmot, Marmota flaviventris, alarm calling that was explained by direct parental care was compared with that variation explained by total r. After pups emerged, adult females with pups called more than other age/sex classes. Additionally, 42% of the variation in the rate of calling over the entire study was a function of whether the caller was a female who had pups emerge above ground that year. Total r explained no significant variation in the rate of alarm calling. Alarm calling in group-living yellow-bellied marmots is a form of direct parental care and inclusive fitness, broadly defined, is of little importance for the maintenance of alarm calling. ? 1997 The Association for the Study of Animal Behaviour When alarmed by predators, many species produce specific vocalizations referred to as alarm calls (Klump & Shalter 1984). Alarm calling may increase the caller’s probability of predation (Sherman 1977, 1985), and the question of why many social animals produce apparently altruistic alarm calls to warn group mates has puzzled biologists for some time (e.g. Maynard Smith 1965; Charnov & Krebs 1975; Smith 1986; Hoogland 1995). Several authors invoked kin selection (Hamilton 1964) as a mechanism to explain some or all of the alarm calling in sciurid rodents (e.g. Dunford 1977; Sherman 1977; Davis 1984; MacWhirter 1992; Hoogland 1983, 1995). Kin selection includes that fitness that individuals gain by helping their descendent kin (direct fitness) and non-descendent kin (indirect fitness) (Brown 1987). By invoking kin selection, sensu Correspondence: D. T. Blumstein, Department of Systematics and Ecology, University of Kansas, Lawrence, KS 66045, U.S.A. (email: [email protected]). J. Steinmetz is at the Illinois Natural History Survey, Center for Acquatic Ecology, 607 E. Peabody Dr., Champaign, IL 61820, U.S.A. 0003–3472/97/010173+12 $25.00/0/ar960286 ? 1 17 lato, without distinguishing the direct and indirect components, researchers imply that indirect fitness benefits are an important driving force behind apparently altruistic behaviours such as alarm calling (but see Dunford 1977, page 784, who noted that although kin selection was important for the evolution of alarm calling, alarm calling was not an ‘altruistic’ behaviour because it was not risky). A more parsimonious explanation (Williams 1966) is that callers primarily produce alarm calls to warn their descendent kin, particularly vulnerable offspring who have much to gain from being warned (Maynard Smith 1965; Shields 1980). Most researchers would not consider such parental care, or more generally, behaviour patterns that increase direct fitness, to be ‘altruistic’, because altruism implies that non-descendants must benefit (Bertram 1982). In support of alarm calling as a way to maximize direct fitness, females of several species call relatively more within a single year, when recently emerged and presumably vulnerable offspring are present (McCarley 1966; Smith 1978; Schwagmeyer 1980; Shields 1980), and/or call more in years when emergent 997 The Association for the Study of Animal Behaviour