Federica Dal Pesco

Across different modalities, signals play a core role in attracting mates and influencing mating success. In several non-human primate species, females produce calls during mating that are thought to promote male competition over receptive females. The extent to which social system characteristics modulate the function of copulation calls remains less clear. We studied copulation calls in wild Guinea baboons ( Papio papio ), who live in a multilevel society structured around units in which females associate and mate almost exclusively with a single male. We hypothesised that females use copulation calls as an indirect form of mate competition, with competition increasing in larger units. In addition, we hypothesised that females are more likely to mate again after calling. We analysed 6116 copulations between 2014 and 2025, involving 99 reproductively active females and 78 subadult and adult males. Females produced copulation calls in 72.7% of copulations, with large inter-individual variation. Neither unit size nor its interaction with the female’s swelling size or the presence of simultaneously receptive females affected the probability of calling. A survival analysis with a subset of the data (2353 copulations) revealed no effect of calling on the latency to the next mating. Our results render the hypothesis that female Guinea baboons use calls in indirect mate competition unlikely. Yet, the probability of calling varied with sexual swelling size, suggesting that calls signal female fertility. Possibly, Guinea baboon copulation calls represent an evolutionary remnant, no longer under selective pressure, and can be considered index signals of female fertility.

The growing field of comparative thanatology aims to shed light on how and why the understanding of death evolved. Observations across different nonhuman primate species have reported care-taking behaviour toward dead infants, but also cannibalism. Various hypotheses have been put forward to explain these behaviours, ranging from responses to infantile cues to an understanding of death. To aid comparative analyses and future tests of these hypotheses, we report behaviours toward dead infants in a wild population of Guinea baboons ( Papio papio ) living in the Niokolo-Koba National Park, Senegal. During 12 years of field observations (2014–2025), we recorded 64 infant deaths within the first year of life. In 22 of these cases, mothers, but occasionally also other group members, carried, protected, groomed, and dragged dead infants. In 6 cases, cannibalism occurred. None of the mothers expressed any signs of emotional distress in response to infant death. We suggest that no concept of death in Guinea baboons needs to be invoked to explain the observed behaviours. Instead, post-mortem caretaking behaviours can be viewed as the by-product of selection for infant care, which includes not abandoning an infant that might temporarily be unresponsive. The lack of infant responses to maternal behaviour, together with the disintegration of the corpse, may drive a shift from perceiving the infants as an object that elicits caretaking to one that is either abandoned or, in some cases, comes to resemble food, ultimately facilitating cannibalism.

Over six decades of research on wild baboons and their close relatives (collectively, the African papionins) have uncovered substantial variation in their behavior and social systems. While most papionins form discrete social groups (single-level societies), a few others form small social units that are nested within larger supergroups (multi-level societies). These two systems are generally thought to be qualitatively distinct, but data from wild populations increasingly suggest that there may be areas of overlap. To quantify this potential gradient in social structure, a more systematic, comparative analysis is needed. Here, we constructed a database of behavioral and demographic records spanning 135 group-years, 28 social groups, 13 long-term field studies, and 11 species to quantify variation in grooming network structure and identify the individual and dyadic properties (e.g., kinship and social status effects) that underlie this variation. Consistent with accumulating field observations, the single-level species could be divided into two categories: cohesive and cliquish . Cohesive single-level networks were dense, kin-biased, and moderately rank-structured, while cliquish single-level networks were more differentiated, slightly more kin-biased, and strongly rank-structured. As expected, multi-level networks were very modular and shaped by females’ ties to specific dominant males but varied in their kin biases. Taken together, these data suggest that in the African papionins i) kin and rank biases are widespread but vary in their strength; ii) male-centered subgroups are exclusive to multi-level systems; and iii) increases in network modularity can emerge in response to heightened nepotism and male-centered clustering.

The growing field of comparative thanatology aims to shed light on how and why the understanding of death evolved. Observations across different nonhuman primate species have reported care-taking behaviour of dead infants, but also cannibalism. Various hypotheses have been put forward to explain these infant-directed behaviours, ranging from responses to infantile cues to an understanding of death. To aid comparative analyses and test some of these hypotheses, we report behaviours directed at dead infants in a wild population of Guinea baboons ( Papio papio ) living in the Niokolo-Koba National Park, Senegal. During 12 years of field observations (2014-2025), 67 infants died before reaching 1 year of age. In 4 cases, we could not establish when the infants had died because the field station was closed due to the COVID-19 pandemic. In 22 of the remaining 63 cases, mothers, but occasionally also other group members, carried, protected, groomed, and dragged dead infants. In 6 cases, cannibalism occurred. None of the mothers expressed any signs of emotional distress in response to infant death. We suggest that a concept of death in Guinea need not be invoked to explain the observed behaviours. Instead, selection appears to have favoured post-mortem caretaking behaviours to avoid abandoning an infant that might temporarily be unresponsive. The lack of infant responses to maternal behaviour and the disintegration of the corpse may drive the transition from perceiving the infants as an object that evokes caretaking to one that resembles food, which ultimately facilitates occurrences of cannibalism.

Primate infants depend on their mothers for nursing, transportation, and survival, but also benefit from other behaviours such as contact, protection, and the mother serving as a model for social learning. During infancy, variation in maternal care ("maternal style") can have profound consequences for infant development and survival. We investigated the link between maternal style and infant growth and survival in wild Guinea baboons (Papio papio). This species lives in a tolerant social system with female-biased dispersal. We used data from N = 80 infants to assess variation in maternal style. The final statistical models comprised data from N = 50 infants for the growth analysis based on Parallel Laser Photogrammetry (PLP) measures of forearm length, and N = 63 infants for the survival analysis. To account for heterogeneity in data, we applied a recently established statistical framework that controls for variation in maternal behaviour with infant age. We found only moderate variation among mothers and no evidence for a link between maternal style and infant growth or survival. Neither infant sex, maternal age, nor NDVI variation, a measure later shown to be a poor indicator of food availability, predicted infant growth or survival. We suspect that, in this population living in a habitat with high carrying capacity, disease and predation have greater effects on infant growth and survival than maternal behaviour. Future studies should consider the interplay between infant behaviour and maternal responses in greater detail to better understand variation in early social development.

Male reproductive success varies within populations. Models explaining reproductive skew largely emphasize dominance, yet the determinants of male reproductive success in egalitarian societies remain poorly understood. Using nine years of behavioral and genetic data from five parties, we investigated male reproductive monopolization in wild Guinea baboons ( Papio papio ), an egalitarian multilevel society with one-male “units” nested within “parties” and low male-male contest competition. Genetic analyses showed 93% of the 71 infants were sired by the female’s “unit male”, with rare extra-unit paternities consistent with limited control models. Within parties, reproduction was shared among multiple unit males, resulting in low reproductive skew, with top males siring 23-40% of offspring, well below levels in hierarchical species. Female takeovers were rare, suggesting male restraint. Reproductive success, assessed as the number of unit females, was positively associated with dominance ratings, yet males with average ratings held the largest units. Prime-age predicted reproductive success better than dominance. In conclusion, male Guinea baboons’ reproductive success is shaped less by dominance than by age and stable associations with females, who play an active role in inter-sexual relationships. These results emphasize the need to move beyond frameworks focused solely on dominance-based mechanisms and to consider species-specific social organization. Significance statement: Current theoretical models of male reproductive success often focus on dominance and males’ ability to monopolize access to females. Yet, less is known about the determinants of reproductive success in societies with egalitarian male relationships, such as the multilevel society of wild Guinea baboons. Using nine years of behavioral and genetic data from five groups (“parties”), we show that unit males almost always sire their unit’s offspring. However, at the party level, male reproductive skew is low. Reproductive success is better predicted by prime-age than dominance and appears to result from long-term associations with females, likely shaped by female choice. Our results highlight the need to examine diverse social systems to understand the evolution of reproductive strategies beyond dominance-centered models.

Over six decades of research on wild baboons and their close relatives (collectively, the African papionins) have uncovered substantial variation in their behavior and social systems. While most papionins form discrete social groups (single-level societies), a few others form small social units that are nested within larger supergroups (multi-level societies). These two systems are generally thought to be qualitatively distinct, but data from wild populations increasingly suggest that there may be areas of overlap. To quantify this potential gradient in social structure, a more systematic, comparative analysis is needed. Here, we constructed a database of behavioral and demographic records spanning 135 group-years, 28 social groups, 13 long-term field studies, and 11 species to quantify variation in grooming network structure, and identify the individual and dyadic properties (e.g., kinship and social status effects) that underlie this variation. Consistent with accumulating observations in the field, the single-level species could be divided into two categories: cohesive and cliquish . Cohesive single-level networks were dense, kin-biased, and moderately rank-structured, while cliquish single-level networks were more differentiated, slightly more kin-biased, and strongly rank-structured. As expected, multi-level networks were very modular and shaped by females’ ties to specific dominant males but varied in their kin biases. Taken together, these data suggest that (i) kin and rank biases are widespread but vary in their strength; (ii) male-centered subgroups are exclusive to multi-level systems; and (iii) increases in network modularity can emerge in response to heightened nepotism and male-centered clustering. SIGNIFICANCE STATEMENT: What forces explain variation in primate societies? While kinship and dominance shape the social lives of many of our close relatives, it is unclear how their effects differ across species. Using a new database comprising decades of field research, we found that baboons and their close relatives fell into three general patterns: one in which groups were cohesive, kin-biased, and moderately rank-biased, another in which groups were more cliquish and nepotistic, and a third in which groups were divided into clusters centered on dominant males. Distinct primate societies may thus reflect differences in the strength of females’ nepotistic biases and the degree of males’ social influence.

Recognizing skilful group members is crucial for making optimal social choices. Whether and how nonhuman animals attribute skill to others is still debated. Using a lever-operated food box, we enhanced the foraging skill of a single male ( the specialist ) in one zoo-housed and two wild groups of Guinea baboon ( Papio papio ). We measured group members' behavioural responses before, during and after our manipulation to reveal whether they focused on the outcome of the male's actions or changed their assessment of his long-term value. During the manipulation, females in the specialist’s unit, but not the wider group, competed over access to the specialist—increasing their grooming of him 10-fold and aggression near him fourfold. Both behaviours were predicted by the amount each female ate from the food box and returned to baseline within 2 weeks of its removal. This behavioural pattern supports an outcome-based assessment where females responded to male-provided benefits (utility) rather than attributing competence (value). By contrast, males from the wider party ate prodigiously from the reward but did not change their behaviour towards the specialist at all—revealing different social strategies corresponding to the social stratification of the Guinea baboon’s multi-level society.