Rapid facial mimicry in Platyrrhini: Play face replication in spider monkeys (Ateles fusciceps, Ateles hybridus, and Ateles paniscus)

Rapid facial mimicry (RFM), the rapid and automatic replication of facial expression perceived, is considered a basic form of empathy and was investigated mainly during play. RFM occurs in Catarrhini (Old World primates), but it is not still demonstrated in Platyrrhini (New World primates). For this reason, we collected video data on playful interactions (Nplay_interactions = 149) in three species of spider monkeys (Ateles fusciceps-N = 11, Ateles hybridus-N = 14, and Ateles paniscus-N = 6) housed at La Vallée des Singes and the ZooParc de Beauval (France). For the first time, we demonstrated the occurrence of RFM in Platyrrhini (analyzing 175 events). Players' sex, age, species, relationship quality, and kinship did not modulate RFM probably due to the species' complex fission-fusion dynamics and flexible interindividual social relationships. Compared to the absence of any playful expressions or the presence of only not replicated play face, RFM prolonged the session duration and was sequentially associated with more types of more intense offensive playful patterns (patterns aimed at attacking/pursuing the playmate). We proposed that RFM may favor synchronization and context sharing between players, thus decreasing the risk of behavior misinterpretation while simultaneously fostering a more competitive nature of play. In conclusion, this study stimulates additional research on the evolutionary origins of motor mimicry in primates, possibly dating back to before the divergence of New and Old World monkeys. Furthermore, it also points toward the possibility that RFM may not always lead to cooperation but also to competition, depending on the context and species' social and cognitive features.

Not just females: the socio-ecology of social interactions between spider monkey males

Male-male relationships are mostly characterized by competition. However, males also cooperate with one another if socio-ecological conditions are suitable. Due to their male philopatry, the need for cooperation in home range defence and high degree of fission-fusion dynamics, spider monkeys provide an opportunity to investigate how male-male interactions are associated with socio-ecological factors, such as the presence of potentially receptive females, the degree of food availability and the likelihood of home range defence. We tested predictions about changes in social interactions between wild spider monkey males in relation to these factors. First, males did not change their interaction patterns when potentially receptive females were in the subgroup compared to when they were absent. Second, males tended to be less tolerant of one another when feeding, but spent more time grooming, in contact and proximity with one another when food availability was lower than when it was higher. Third, males exchanged fewer embraces, spent less time grooming, in proximity and in contact with one another, and spent more time vigilant at the home range boundary area than at other locations. Our findings contribute to the understanding of social flexibility and the importance of considering males in socio-ecological models of any group-living species.

Dispersal patterns in black howler monkeys (Alouatta pigra): Integrating multiyear demographic and molecular data

Dispersal is a fundamental process in the functioning of animal societies as it regulates the degree to which closely related individuals are spatially concentrated. A species' dispersal pattern can be complex as it emerges from individuals' decisions shaped by the cost-benefit tradeoffs associated with either remaining in the natal group or dispersing. Given the potential complexity, combining long-term demographic information with molecular data can provide important insights into dispersal patterns of a species. Based on a 15-year study that integrates multiyear demographic data on six groups with longitudinal and cross-sectional genetic sampling of 20 groups (N = 169 individuals, N = 21 polymorphic microsatellite loci), we describe the various dispersal strategies of male and female black howler monkeys (Alouatta pigra) inhabiting Palenque National Park, Mexico. Genetically confirmed dispersal events (N = 21 of 59 males; N = 6 of 65 females) together with spatial autocorrelation analyses revealed that the dispersal pattern of black howlers is bisexual with strong sex-biases in both dispersal rate (males disperse more often than females) and dispersal distance (females disperse farther than males). Observational and genetic data confirm that both males and females can successfully immigrate into established groups, as well as form new groups with other dispersing individuals. Additionally, both males and females may disperse singly, as well as in pairs, and both may also disperse secondarily. Overall, our findings suggest multiple dispersal trajectories for black howler males and females, and longer multiyear studies are needed to unravel which demographic, ecological and social factors underlie individuals' decisions about whether to disperse and which dispersal options to take.

Factors influencing establishment success in reintroduced black-faced spider monkeys Ateles chamek

Establishing reintroduced primates in a suitable predetermined area has proven to be a challenge. Establishment is the first major step that has to be taken in the long process of reintroduction. When this first goal is not achieved, the chances of success decline drastically. Understanding the main determinants of establishment is therefore crucial for reintroduction success. This study examined the influence of three independent factors on the establishment success of reintroduced spider monkeys. We analysed data from the releases of eight groups of black-faced spider monkeys (Ateles chamek), which are part of the official reintroduction program of spider monkeys in the South Eastern Peruvian Amazon. Establishment success was measured by the proportion of individuals within groups that were found in the target area 6 months after release. The hours research assistants and volunteers spent with the group within the first 3 months after release-in the context of post-release monitoring-was shown to have a positive effect on the establishment success of the released group in the target area. The presence of an already established group in the area was also found to have a significant positive effect on establishment success. The influence of the days of post-release food provisioning had no effect. Our findings emphasize the importance of long-term monitoring programs to help increase the efficiency of primate reintroductions.

Who’s there? Third parties affect social interactions between spider monkey males

Spider monkeys provide an intriguing opportunity to examine behavioural flexibility in relation to their social environment given their high degree of fission–fusion dynamics and the nature of male–male relationships. These characteristics allow us to examine how flexibility in social interactions is modulated by the perception of risk and uncertainty related to other group members. We investigated whether male–male interactions vary according to partner identity and presence of third parties in wild Geoffroy’s spider monkey (Ateles geoffroyi). We used proportion of approaches followed by an embrace, an indicator of risk and uncertainty, or by grooming, an affiliative behaviour. To confirm the monkeys’ perception of risk or uncertainty we used aggression rates and time spent vigilant. We collected data on eight adult spider monkey males: three of them belonged to one clique and the other five to another clique based on distinct patterns of residence. We found higher proportions of approaches followed by embraces and lower proportions of approaches followed by grooming between males of different cliques than between males of the same clique. In addition, we found higher aggression rates between males from different cliques. The proportions of approaches followed by embraces in the five-male clique were higher when the three-male clique was no longer in the group. The five males were more vigilant when the other three males were present in the group, indicating the monkeys perceived higher risk or uncertainty under these circumstances. We found lower proportions of approaches followed by grooming between two males when there was at least one other male in the subgroup than when there were only the two males. Our results provide evidence for behavioural flexibility in the interactions between spider monkey males as an example of how animals can cope with social challenges by adjusting their behaviour.

Network analysis as a tool to understand social development in spider monkeys

The emerging field of network science has demonstrated that an individual's connectedness within their social network has cascading effects to other dimensions of life. Like humans, spider monkeys live in societies with high fission-fusion dynamics, and are remarkably social. Social network analysis (SNA) is a powerful tool for quantifying connections that may vary as a function of initiating or receiving social behaviors, which has been described as shifting social roles. In primatology, the SNA literature is dominated by work in catarrhines, and has yet to be applied to the study of development in a platyrrhine model. Here, SNA was utilized in combination with R-Index social role calculation to characterize social interaction patterns in juvenile and adult Colombian spider monkeys (Ateles fusciceps rufiventris). Connections were examined across five behaviors: embrace, face-embrace, grooming, agonism, and tail-wrapping from 186 hr of observation and four network metrics. Mann-Whitney U tests were utilized to determine differences between adult and juvenile social network patterns for each behavior. Face-embrace emerged as the behavior with different network patterns for adults and juveniles for every network metric. With regard to social role, juveniles were receivers, not initiators, for embrace, face-embrace, and grooming (ps < .05). Network and social role differences are discussed in light of social development and aspects of the different behaviors.

Demography and life history of a group of white-bellied spider monkeys (Ateles belzebuth) in western Amazonia

Species-specific demographic parameters and life history variables are important for understanding how individual primate taxa have adapted to evolutionary and ecological pressures and for conducting interspecific comparisons as well as for conducting population viability analyses and for managing captive populations. Here, we describe results from a 12+ year study of the demographic dynamics of a wild group of white-bellied spider monkeys (Ateles belzebuth belzebuth) living near the Tiputini Biodiversity Station in a largely pristine rainforest in western Amazonia. Across the study period, group size varied between 25 and 37 individuals, and there was a clearly female-biased sex ratio within all age classes. Females were the dispersing sex, as 19 females born into the group disappeared close to reaching adult body size and were presumed to have emigrated, while seven subadult or adult females joined the group during the study period. We estimated the age of dispersal for females at 5.9 ± SD 0.4 years (N = 13). Our study confirms that males are the philopatric sex, as all natal males have remained in the group and some have begun to reproduce, while no males have immigrated. Males began ranging independently from their mothers at ∼4.5 years of age and began copulating with adult females by the age of ∼5 years. Females had long inter-birth intervals (44.2 ± SD 7.8 months; range: 32-64 months, N = 21). Based on our data, female spider monkeys might have longer life spans than males, as only one out of six adult males but 9 out of 11 adult females present in the group in mid 2005 were still present in January 2018. The slow development and extended life histories of wild spider monkeys pose significant challenges for the ability of these primates to cope with habitat degradation and hunting throughout their geographical distribution.

Homosexual Behavior Between Male Spider Monkeys (Ateles geoffroyi)

Homosexual behavior is defined as genital contact or genital manipulation between same-sex individuals. In nonhuman primates, it may regulate social relationships by serving as a means of reconciliation, tension alleviation, or alliance formation. Grappling is a rare and complex behavior, which most frequently occurs between same-sex individuals of the genus Ateles and can include mutual manipulation of the genitalia. Here we report three cases of penile-anal intromission during grappling between wild male spider monkeys living in the natural protected area of Otoch Ma'ax Yetel Kooh, Mexico. In all the observed cases, the same adult male was the actor. To our knowledge, this is the first report of penile-anal intromission between males in any New World primate species.

Quality and overlap of individual core areas are related to group tenure in female spider monkeys

In species with a high degree of fission-fusion dynamics group members may differ in the use of the group home range to reduce food competition. Such differential use may result in distinct individual core areas. We studied core area quality and overlap among 21 female spider monkeys belonging to the same group over a period of 4 years. Core areas ranged between 62 and 161 ha with a mean overlap of 56% between any given two females. Only a small portion (mean = 3 ha) of each individual core area was used exclusively. No single part of the home range was used as core area by all females, and only an area of less than 1 ha was used as part of the core area by 20 of the 21 females. The time a female spent in the group (i.e., group tenure) was associated with characteristics of the core areas: the longer the group tenure, the better the quality of her core area. In addition, the longer the time two females spent together in the same group, the larger the overlap between their individual core areas. As this result was obtained while controlling for the time two females spent together in the same subgroup, females may reduce direct competition by using the same resource at different times. In sum, spider monkey females' group tenure plays a central role in the quality and overlapping patterns of their individual core areas.

Genetic analyses suggest no immigration of adult females and their offspring into the Sonso community of chimpanzees in the Budongo Forest Reserve, Uganda

Chimpanzees are frequently used to illustrate the relationship between sex differences in dispersal and sex differences in cooperation in primates and other group-living mammals. Male chimpanzees are highly philopatric, typically remaining in their natal communities for their entire lives to cooperate with related males in competition against less related males from other groups, whereas females typically disperse once at adolescence and cooperate with each other less frequently. However, there have been a few reports of dependent male offspring joining groups when their mothers transferred between communities as adults. Although such events are difficult to document, determining how often they actually occur is important for elucidating the links between philopatry, kinship, and cooperation in both chimpanzees and group-living animals more generally. Here we use genetic analyses to investigate a previous report of a large-scale transfer of many females and their offspring into the Sonso community of chimpanzees in the Budongo Forest Reserve, Uganda. Using autosomal microsatellite genotypes, we assigned a Sonso father to ten of the fourteen putative immigrants, and found that the four putative immigrants for whom we could not assign a Sonso father (perhaps due to incomplete sampling of all Sonso candidate fathers) nevertheless had Y-chromosome microsatellite haplotypes that were common in Sonso males but absent in males from four other chimpanzee communities at Budongo. These results suggest that these putative immigrant females and their offspring were probably actually long-term residents of Sonso whose identifications were delayed by their peripheral or unhabituated status. These results are consistent with other genetic and behavioral evidence showing that male between-community gene flow is exceedingly rare in east African chimpanzees.

Males follow females during fissioning of a group of northern muriquis

Although well documented in matrilocal primate species, group fission is still a poorly known phenomenon among patrilocal primates. In this paper we describe in detail a group fission event in the population of northern muriquis at the Reserva Particular do Patrimônio Natural-Feliciano Miguel Abdala in Caratinga, Minas Gerais, Brazil, using Social Network Analyses (SNA). Data on association patterns were collected during systematic observations from May 2002 to September 2005, and analyzed for dry (from May to October) and rainy seasons (from November to April). The fission process started with subgroup formation in the rainy season 2002-2003, and was completed by the dry season of 2003. By the dry season 2003, the parent group (Jaó) had fissioned to form a second mixed-sex group (Nadir) while a subgroup of males (MU) moved between the parent group and the newly established group. Before the Jaó group fission started (dry season 2002) and during its initial phases (rainy season 2002-2003), females that ultimately composed the daughter group (Nadir) were the most peripheral in the association network. In the rainy season 2002-2003, the median monthly (N=6) operational sex ratio (OSR) of Jaó group was 2.81. However, once Jaó females initiated the fissioning process to establish the Nadir group, the OSR was more favorable to males in the Nadir group than in the Jaó group. Our results suggest that males followed the females to escape an unfavorable OSR in their natal group.