An investigation into the hygienic function of allogrooming in capuchin monkeys (Cebus apella): grooming of different body regions in relation to surface area

Abstract

The evolutionary origin of allogrooming behaviour is generally accepted to be hygiene. In recent years this function has received little interest from scientific research while the relatively new social functions are repeatedly studied in a wide variety of species. The discussion of allogrooming having multiple functions (namely in primates) has been reviewed numerous times; however, hygiene is often ignored or is considered through implicit reference only. The aim of this investigation was to examine the importance of hygiene in the allogrooming behaviour of capuchin monkeys (Cebus apella). This species has never before been thoroughly studied for allogrooming in the context of hygiene. Previous work by Pérez and Veà Baró (1999) examined the hygienic function of allogrooming in the white-crowned mangabey (Cercocebus torquatus lunulatus) and gave evidence supporting this function. Their analyses were marred by the use of percentages in a chi-square test. This investigation repeats the analysis of Pérez and Veà Baró (1999) with the intention of highlighting these errors and providing suitable alternative approaches to data analysis. In doing so the study provides significant data in support of grooming for hygiene. These results are based on a large sample size (5 focal females, 153 hours of observations) and show a high level of grooming activity. The focal females observed were involved in alloG bouts for 5.94% of observation time. The work by Pérez and Veà Baró (1999) and the current investigation support the evidence of Barton (1983a, b, 1985) and Hutchins and Barash (1976) for the importance of hygiene in primate allogrooming. The study also shows that the support for the hygienic function does not discredit any of the alternative functions hypothesised. Indeed, the data suggest that other "more social” functions are in operation and can be seen in the variation between individuals and across observation periods. A discussion of the multiple functions of grooming and consideration of a "multiple functions" hypothesis will also be made in this investigation. It will also be discussed how allogrooming, in the context of hygiene, can benefit both the groomer and groomee without the need to invoke models such as reciprocal altruism or kin selection.