Biology subjects

Carter, A. J.

Publications and source records attributed to Carter, A. J..

4 recordsLinked to original sources

bioRxiv2025

Disparate social structures are underpinned by distinct social rules across a primate radiation

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 STATEMENTWhat 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.

animal behavior and cognition↗

bioRxiv2022

Female chacma baboons modulate their sexual receptivity in response to male coercion

Research in social mammals has revealed the complexity of strategies females use in response to female-female reproductive competition and sexual conflict. One point at which competition and conflict manifests acutely is during sexual receptivity, indicated by swellings in some primates. Whether females can adjust their sexual receptivity from cycle to cycle to decrease reproductive competition and sexual conflict in response to changes in the social environment has not been tested. As a first step, this study explores whether sexual receptivity duration is predicted by the social environment in wild female chacma baboons (Papio ursinus). Given that female baboons face intense reproductive competition and sexual coercion, we predicted that: females could shorten the duration of their sexual receptive period to reduce female-female aggression and male coercion or increase it to access multiple or their preferred male(s). We quantified 157 ovulatory cycles from 46 wild females living in central Namibia recorded over 15 years. We found no support for our hypothesis; however, we found a negative correlation between maximal-swelling duration and group size, a proxy of within-group competition. This study provides further evidence that swelling is costly for females as well as a testable framework for future investigations of cycle length manipulation.

animal behavior and cognition↗

bioRxiv2021

Breeding seasonality generates reproductive trade-offs in a long-lived mammal

The evolutionary benefits of reproductive seasonality are usually measured by a single fitness component, namely offspring survival to nutritional independence (Bronson, 2009). Yet different fitness components may be maximised by dissimilar birth timings. This may generate fitness trade-offs that could be critical to understanding variation in reproductive timing across individuals, populations and species. Here, we use long-term demographic and behavioural data from wild chacma baboons (Papio ursinus) living in a seasonal environment to test the adaptive significance of seasonal variation in birth frequencies. Like humans, baboons are eclectic omnivores, give birth every 1-3 years to a single offspring that develops slowly, and typically breed year-round. We identify two distinct optimal birth timings in the annual cycle, located 4-months apart, which maximize offspring survival or minimize maternal interbirth intervals (IBIs), by respectively matching the annual food peak with late or early weaning. Observed births are the most frequent between these optima, supporting an adaptive trade-off between current and future reproduction. Furthermore, infants born closer to the optimal timing favouring maternal IBIs (instead of offspring survival) throw more tantrums, a typical manifestation of mother-offspring conflict (Maestripieri, 2002). Maternal trade-offs over birth timing, which extend into mother-offspring conflict after birth, may commonly occur in long-lived species where development from birth to independence spans multiple seasons. Such trade-offs may substantially weaken the benefits of seasonal reproduction, and our findings therefore open new avenues to understanding the evolution of breeding phenology in long-lived animals, including humans. SIGNIFICANCE STATEMENTWhy some species breed seasonally and others do not remain unclear. The fitness consequences of birth timing have traditionally been measured on offspring survival, ignoring other fitness components. We investigated the effects of birth timing on two fitness components in wild baboons, who breed year-round despite living in a seasonal savannah. Birth timing generates a trade-off between offspring survival and future maternal reproductive pace, meaning that mothers cannot maximize both. When birth timing favours maternal reproductive pace (instead of offspring survival), behavioural manifestations of mother-offspring conflict around weaning are intense. These results open new avenues to understand the evolution of reproductive timings in long-lived animals including humans, where such reproductive trade-offs may commonly weaken the intensity of reproductive seasonality.

evolutionary biology↗

bioRxiv2021

Why do some primate mothers carry their infant's corpse? A cross-species comparative study

Non-human primates respond to the death of a conspecific in diverse ways, some which may present phylogenetic continuity with human thanatological behaviours. Of these responses, infant corpse carrying by mothers (ICC) is the most-frequently reported. Despite its prevalence, quantitative analyses of this behaviour are scarce and inconclusive. We compiled a database of 409 published cases across 50 different primate species of mothers responses to their infants deaths to test hypotheses proposed to explain between- and within-species variation in corpse carrying. Using Bayesian phylogenetic regressions, we preliminarily identified three factors as possible predictors of ICC occurrence. However, using an information-theoretic approach, no combination of these predictors performed better than the null model, offering no support for any of the hypotheses we tested. In contrast, for those cases where infants corpses were carried, infant age affected ICC duration, with longer ICC observed for younger infants. This result may provide support for hypotheses that suggest that ICC is a by-product of a strong mother-infant bond. The results are discussed in the context of the evolution of emotion and their implications for evolutionary thanatology are considered.

animal behavior and cognition↗