Does allogrooming serve a hygienic function in Cercocebus torquatus lunulatus?

To test the hygienic functional hypothesis of allogrooming in the white-cro wned mangabey (Cercocebus torquatus lunulatus), we analyzed the distributio n of such behavior over the body surface in the individuals of two captive groups of this species (N = 9 and N = 8). To sample the data, we used focal animal sampling and continuous recording. Before analyzing the data, we me asured a representative subject in order to calculate the body surface area occupied by each site, defined accessibility rigorously (distinguishing am ong three categories of sites: easy to reach, difficult to reach, and inacc essible), and tested empirically the classification proposed. To determine whether allogrooming was likely to concentrate on the body sites with acces sibility problems, we ran three successive analyses, each of with was incre asingly specific: grouping types of sites, analyzing each site separately, and analyzing each subject's reception profile. The results obtained show t hat in both groups inaccessible sites received more allogrooming than predi cted by their actual surface area; sites that were difficult to reach recei ved an amount of allogrooming proportional to the body surface area they oc cupied, and those easy to reach received less allogrooming than expected. T his complementarity between the distribution of auto- and allogrooming is c onsistent with the hygienic functional hypothesis of allogrooming. However, not all inaccessible sides nor those difficult-to-reach were allogroomed e qually: Allogrooming concentrated primarily on dorsal and caudal regions, w hose care is incompatible with a ventral/ventral orientation between groome r and groomee. The strong distributional selectivity of allogrooming and th e interindividual variability in preferred allogrooming sites suggest that the hygienic functional hypothesis cannot fully account for all the aspects of the corporal distribution of such behavior. Thus, in support of the mul tifunctional nature of allogrooming, we conclude that there must be more th an cleaning involved in Cercocebus torquatus lunulatus' allogrooming. (C) 1 999 Wiley-Liss, Inc.