Charting the neglected West: The social system of Guinea baboons

Abstract

Objectives: Primate social systems are remarkably diverse, and thus play a central role in understanding social evolution, including the biological origin of human societies. Although baboons have been prominently featured in this context, historically little was known about the westernmost member of the genus, the Guinea baboon (Papio papio).

Material and methods: Here, we summarize the findings from the first years of observations at the field site CRP Simenti in the Niokolo Koba National Park in Senegal.

Results: Guinea baboons reveal a nested multi-level social organization, with reproductive units comprising one "primary" male, one to several females, young, and occasionally "secondary" males at the base of the society. Three to five units form "parties," which team up with other parties to form a "gang." Different gangs have largely overlapping home ranges and agonistic interactions between different parties or gangs are rare. Some but not all strongly socially bonded males are highly related, and population genetic and behavioral evidence indicate female-biased dispersal. Females play an important role in intersexual bond formation and maintenance, and female tenure length varies between a few weeks to several years.

Discussion: While the social organization resembles that of hamadryas baboons (P. hamadryas), the social structure differs considerably, specifically in terms of low male aggressiveness and female freedom. Despite substantial differences in social organization and social structure, the acoustic structure of Guinea baboon vocalizations does not differ substantially from that of other baboon taxa. With its multi-level organization, stable bonds between males and females, as well as a high-degree of male-male cooperation and tolerance, Guinea baboons constitute an intriguing model for reconstructing human social evolution.

Keywords: Guinea baboons; Papio papio; female dispersal; human evolution; nested multi-level society; primate evolution; social system.

Figure 1

Distribution of the six Papio species. Species distributions are modified from Zinner et al. (2013). Baboon drawings by Stephen Nash

Figure 2

(a) Map of Senegal with the location of the Niokolo Koba National Park. The field site CRP Simenti lies next to the Gambia river (b). Hygrothermic climograph of the Tambacounda region according to Walter and Lieth (1967). Depicted are monthly temperatures (mean, min, max) in relation to monthly precipitation. Based on the assumed dependency between evaporation and temperature (e.g., monthly Ø 10 °C evaporates 20 mm, and Ø 20 °C evaporates 40 mm), the climograph demarcates periods of aridity, i.e., dry season and humidity, i.e. wet season. Meteorological data was recorded at the Tambacounda Weather Station (ID: GHCND:SG000061687) and derived from the National Oceanic and Atmospheric Administration (NOAA; http://www.ncdc.noaa.gov/cdo-web/). (c) Home range overlap of three of the study gangs at Simenti. Location data was collected by means of GPS‐enabled collars over a three‐year period (2010–2012). Kernel home ranges (fixed KDE) were modeled using the rule‐based ad‐hoc method (Kie, 2013). Dashed lines depict the home ranges (95% contour) and solid lines the core areas (50% contour). The numbers represent the most important wetlands (Mare) in our study region: (1) Mare Simenti, (2) temporary Mare, (3) Mare Kountadala, (4) Mare Nanaka

Figure 3

Boxplot with median, IQR, and minimum and maximum values (a). Adult female and adult male body mass. (b) Correlation between maxillary canine height and body mass. (c) Correlation between testicular volume and adult male body mass

Figure 4

Dendrograms derived from a hierarchical cluster analysis of the association indices among nine adult males during the 2010 observation period (n = 36 dyads) and among 16 adult males during the 2011 observation period (n = 120 dyads). Letter codes represent individual males (from Patzelt et al., 2014)

Figure 5

Social organization within a gang of Guinea baboons, based on proximity scans (unpublished data) collected during a 2‐month period in 2013 from the Simenti gang. One‐male‐units, some with secondary males (small squares), team up to form “parties,” which in turn form larger aggregations (“gangs”). The number of females per male varies considerably, as does female tenure length (Goffe et al., 2016). Females may maintain relations with females outside their own unit or party (Goffe et al. in preparation)

Figure 6

Vocal Repertoire of Guinea baboons. Discriminant function analyses using the six identified call clusters as grouping variable. The classification procedure revealed a high overall classification success with 99.2% of calls correctly assigned to the respective call type. For each call‐cluster a representative spectrogram is shown (modified from Maciej, Ndao, et al., 2013)