Elsevier

Behavioural Processes

Volume 180, November 2020, 104240
Behavioural Processes

Conflict over grooming topography between mandrill groomers and groomees

https://doi.org/10.1016/j.beproc.2020.104240Get rights and content

Highlights

  • In mandrills, the groomer primarily determines grooming topography.

  • Groomers preferred to groom "safe" areas (the back and rump).

  • Groomees tries to orient grooming towards unsafe areas.

  • Groomers and groomees conflicted over grooming topography.

Abstract

Grooming directed to different body areas is likely to imply different costs and benefits for groomers and groomees. In this study, we investigated social influences on grooming topography in captive female mandrills (Mandrillus sphinx). Subordinate groomers preferred to direct grooming to "safe" areas (the back and rump) compared to dominant groomers, while subordinate groomees did not solicit preferentially grooming to safe areas. Groomers tended to initiate grooming episodes from safe areas, while groomees solicited the switch to unsafe areas. Our results highlight a previously unrecognized source of conflict between the partners of grooming, one of the most common cooperative interactions in animals.

Introduction

Allogrooming (grooming, hereafter) is probably the most common cooperative behaviour among mammals and birds (Dunbar, 1991; Kenny et al., 2017), where it plays an important role in reducing ectoparasite load (Tanaka and Takefushi, 1993; Clayton et al., 2010; Akinyi et al., 2013). Grooming also implies costs for both the groomer and groomee in terms of reduced vigilance and risk of aggression associated to the close proximity that it necessarily requires (Maestripieri, 1993; Cords, 1995; Schino and Alessandrini, 2015; Blanchard and Pays, 2017). Given that both fur structure and density and ectoparasite load vary along the body surface, it is likely that the different areas of the body need different amounts of grooming, and thus that grooming in the different areas implies different benefits (Zamma, 2002). Similarly, the costs of grooming are also likely to be modulated by the area grooming is directed to. For example, it is possible that grooming directed to the face of another individual (which greatly facilitate eye contact and biting) implies a greater risk of aggression than grooming directed to the tail.

Grooming directed to different body areas seems thus to imply different costs and benefits. Surprisingly, only a tiny fraction of the vast grooming literature takes into account the area of the body grooming is directed to (i.e., its topography). Most studies of the topography of grooming tested the relationships between selfgrooming and allogrooming. These studies showed allogrooming is often directed to areas of the body that cannot be easily reached by selfgrooming, and thus emphasized the hygienic function of allogrooming (Hutchins and Barash, 1976; Barton, 1985; Borries, 1992; Radford and Du Plessis (2006)). Implicitly, these studies also assumed the topography of grooming is mostly under the control of the groomee.

Primate studies that investigated how social factors affect the topography of grooming yielded inconsistent results (see Radford and Du Plessis (2006) for a rare nonprimate example). McKenna (1978) observed that in langurs (Semnopithecus entellus) grooming occurring in the aftermath of aggression was more often directed to the back of the groomee than grooming occurring in more relaxed contexts. Boccia et al. (1982; in rhesus macaques, Macaca mulatta) and Franz (1999; in bonobos, Pan paniscus) reported that subordinate groomers targeted the back of the groomee more often than dominant groomers, while Moser et al. (1991; in long-tailed macaques, M. fascicularis) and Borries (1992, in langurs) found the opposite. The different studies also disagreed over the roles of groomers and groomees in determining the areas being groomed. Franz (1999) and Allanic et al. (2020; both in bonobos) concluded that the groomer is primarily responsible for determining grooming topography, while Boccia et al. (1982) and Borries (1992) suggested it is the groomee that guides grooming interactions. The former three studies reached their conclusion on the basis of the proportion of grooming episodes or of changes in target areas that were preceded by a solicitation. The latter on the basis of the observation that subordinates receive more grooming to safe areas such as the back. Gupta and Sinha (2016, in bonnet macaques, M. radiata) found that grooming solicitations were highly effective in directing grooming to specific areas of the body, but virtually no study examined explicitly the role of grooming solicitations in influencing grooming topography.

In this study, we investigated grooming topography among captive female mandrills (Mandrillus sphinx), and examined the effects of social factors such as dominance rank and kinship on the behaviour of groomers and groomees. By separately analysing grooming solicitations and grooming that was not preceded by a solicitation we were able to assess the preferences of groomees and groomers for grooming directed to different body areas and showed that grooming topography constitutes a previously unrecognized source of conflict between primate groomers and groomees.

Section snippets

Subjects and housing

Subjects of this study were the 9 female members of a captive group of mandrills living in the Rome zoo (Bioparco). The group (that also included one adult male) was housed in a 240 m2 outdoor enclosure connected to indoor quarters. The enclosure was enriched with trunks, ropes and perches. Mandrills were fed twice a day with vegetables, fruits, seeds and monkey chow, while water was available ad libitum. The composition of the group had been stable since 2008, except by births and deaths.

A

Descriptive data

We recorded a total of 1162 grooming episodes among female mandrills. On average, these grooming episodes were directed to 2.17 different body areas (range: 1–26; see Table 1 for details on grooming duration). Overall, mandrills groomed for about 10 % of the observation time. We recorded a total of 470 grooming solicitations, directed to all body areas except the forearm. Overall, 47 % of grooming and 35 % of solicitations were directed to "safe" areas (i.e., the back and rump).

We recorded 1357

Discussion

The results of this study show that mandrill groomers and groomees have different preferences regarding the area to groom or to be groomed. Subordinate groomers preferred to direct grooming towards the back and rump of the groomee. Grooming in these areas is presumably safer, as it allows to avoid direct eye contact and requires the groomee to first turn towards the groomer in case of attack (thus giving the groomer more time to flee). Groomers also tended to initiate grooming from these same

CRediT authorship contribution statement

Gabriele Schino: Conceptualization, Formal analysis, Writing - original draft. Francesco De Angelis: Formal analysis, Investigation, Writing - review & editing.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgements

We thank the Rome zoo (Bioparco) for collaboration and for allowing us access to their mandrill colony. We also thank Giorgio Manzi for his support. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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