Intergroup relations and home range use in Verreaux's sifaka (Propithecus verreauxi)

Relationships between neighboring groups feature prominently in socioecological theory, but few empirical studies have focused on the effects of neighbors on the behavior of primates. Interactions between neighboring groups are most conspicuous during intergroup encounters, but the likelihood of encounters with neighbors can also affect ranging and activity patterns indirectly, and, as a result, behavioral patterns in areas of exclusive use may differ from those in overlap areas of adjacent home ranges. The aim of this study was to examine intergroup relations and spatial variation in home range use in Verreaux's sifaka (Propithecus verreauxi) during the annual mating season. Based on 230 hr of focal animal data collected from ten members of five adjacent groups, we found that behavioral patterns and patterns of resource utilization were not markedly different between areas of exclusive use and overlap areas of adjacent home ranges. Group cohesion tended to be higher in overlap than in core areas, but the proportion of time spent resting and foraging did not differ between these two areas. However, dominant males exhibited a higher scent-marking rate in overlap areas. Observations during intergroup encounters revealed that chases between males occurred frequently, whereas fights involving physical contact were not observed. We also found that the intergroup dominance hierarchy depended on the relative group size or the number of males in each group, with groups of lower dominance rank exhibiting a tendency to sleep proportionally more often in their core areas. The results of this study suggest that in primate species with a moderate level of intergroup aggression, such as Verreaux's sifaka, the possibility of encountering neighbors in areas of home range overlap does not exert strong influence on their behavior and resource utilization.     

Patterns of range use,range defense,and intergroup spacing in moustached tamarin monkeys (Saguinus mystax)

In this paper we examine patterns of group spacing and habitat utilization in neighboring groups of marked free-ranging moustached tamarin monkeys (Saguinus mystax) inhabiting Padre Isla, a small island in the Amazon Basin of northeastern Peru, and describe the set of behavioral mechanisms used by tamarins to maintain the spatial isolation and social integrity of individual groups. Specifically, we address a series of questions regarding the importance of resource defense, mate defense, and territorial defense in intergroup interactions. From June through November 1990, we recorded 67 intergroup interactions involving members of our two main study groups. These interactions occurred at a rate of .14/observation hour and were of two general types. Vocal battles averaged 18 min in duration and were characterized by a series of high frequency, short syllable, long calls that were exchanged between groups separated by distances of greater than 25 m. Aggressive encounters averaged 26 min in duration and involved visual contact, alarm calls, scent marking, and sequences of chases and retreats. Intergroup confrontations did not cluster around the perimeter of a group's home range, and there was no evidence that moustached tamarins patrolled range borders. Our data indicate that 35% of aggressive encounters occurred in the vicinity of major feeding trees. Priority access to these sites is likely to have an important influence on tamarin foraging success. Mate defense and the exploration of new breeding opportunities also appear to be important functions of intergroup conflicts. Not only did the frequency of aggressive encounters increase during breeding periods, but three-fourths of all observed copulations occurred during or within 30 min of an encounter. Given the high degree of reproductive competition reported among tamarin females and the time and energy group members devote to intergroup aggression, maintaining access to a stable home range and the resources contained within that range appear to be critical functions of moustached tamarin social interactions.     

Aggressive intergroup encounters in two populations of Japanese macaques (Macaca fuscata)

It is predicted that variation in intergroup relationships in group living primates reflects the cost and benefit of resource defense. We tested the applicability of the model by examining population difference, group difference, and seasonal difference in behaviors during intergroup encounters in two populations of Japanese macaques (Macaca fuscata), one of six groups from Yakushima Island, and the other of three groups from Kinkazan Island. We found that the nature of intergroup encounter varied with group identity, reproductive seasonality, and population. Yakushima groups showed aggressive behaviors more frequently than did Kinkazan groups and the difference was consistent with the food competition model, both because of the involvement of females, and because home ranges were smaller on Yakushima than on Kinkazan, and thus more defensive. Both sexes of animals participated in aggressive interactions, but males were more aggressive than females. Furthermore, Yakushima population showed more agonistic intergroup behaviors during the mating season than the non-mating season. Also during the encounters, intergroup mating was observed, but only in Yakushima. It is concluded that intergroup relationships reflect the mate guarding behavior by group males. However, the agonistic relationship during non-mating season, especially that of among females, is also consistent with the food competition model. It is also noted that males' behavior toward other groups can also be interpreted as a form of investigative behavior before possible transfer into a new group.     

Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.     

Against all odds: Numerical assessment by tufted capuchin monkeys

When competitors are able to assess the asymmetry in the resource holding potential before interacting, individuals or groups should avoid interacting with stronger opponents, thereby avoiding the energy costs and risk of injury associated with aggressive intergroup encounters. Thus, escalated aggression is expected only between closely matched competitors. Among Argentine tufted capuchin monkeys (Sapajus nigritus), intergroup dominance is decided by the asymmetry in male group size. Using playback experiments, I simulated intergroup encounters with neighboring groups, manipulating both the apparent numerical asymmetry and the resource context. During experimental trials, I recorded the approach behavior of the focal individual, as well as changes in neighbor density and individual travel speed following the presentation of the playback stimulus, to assess whether individual willingness to participate in resource defense was affected by the probability of winning the encounter. In spite of the competitive disadvantage, neither males nor females showed a decreased probability of approach when the numerical odds strongly favored the opposing group. Instead decisions regarding whether to participate appear to be driven primarily by the resource context. Nevertheless, changes in individual behavior during approaches suggest that tufted capuchin monkeys are sensitive to the relative odds. Individuals accelerated less when approaching a larger group, although no changes in neighbor density were apparent. The absence of an effect of the numerical asymmetry on willingness to approach the playback speaker suggests that subordinate groups benefit from engaging in intergroup aggression with larger neighbors, despite the high probability of losing. These encounters may serve to assess the current subjective resource valuation of the neighboring group or limit territorial expansion by large groups by decreasing the marginal value of home range exclusivity. Because these encounters are riskier, however, individuals appear to alter their approaches, becoming more tentative as the numerical odds increasingly favor the opposing group.     

Social system of the Alaotran gentle lemur (Hapalemur griseus alaotrensis): genetic characterization of group composition and mating system

Group composition and mating system were investigated in wild Alaotran gentle lemurs (Hapalemur griseus alaotrensis) using genetic markers. These small-bodied herbivorous and cathemeral primates are endemic to the reed and papyrus beds around Lac Alaotra in Madagascar. They live in small groups in small, defended territories. Data were collected during the rainy seasons in 1996, 1997, and 1999, and include 99 individuals from 22 neighboring social groups and an additional 30 animals from other areas representing most of the geographic range. Animals were located by researchers canoeing in the marshes bordering the lake. After a group's size was determined by direct observation, all individuals were captured, marked, and released. During handling each individual was weighed and sexed, and hair samples for DNA extraction were collected. A 342 bp mtDNA control region sequence and 10 nuclear microsatellite loci provided multilocus genotypes that were used to assess pedigree relations and population structure. Alaotran gentle lemurs were found in groups of two to nine individuals (mean: 4.3), comprising one or two breeding females, their offspring, and one reproducing male. Solitary individuals of both sexes were encountered rarely. Breeding females were the permanent core of the social groups, whereas intergroup transfer of reproductive males was relatively frequent. Forty percent of all reproducing groups contained two breeding females, which were related to each other as closely as mother-daughter or full sisters. Parentage assessment revealed a variable mating system ranging from serial monogamy to polygyny within social groups. At least 8% of paternities involved extragroup males. Additional data on life history and reproduction are presented, and the social system of the Alaotran gentle lemur is discussed in the light of the new genetic findings.     

Consequences of lethal intragroup aggression and alpha male replacement on intergroup relations and home range use in tufted capuchin monkeys (Cebus apella nigritus)

In conflicts between primate groups, the resource-holding potential (RHP) of competitors is frequently related to group size or male group size, which can remain relatively constant for long periods of time, promoting stable intergroup dominance relationships. Demographic changes in neighboring groups, however, could introduce uncertainty into existing relationships. Among tufted capuchin monkeys (Cebus apella nigritus), dominant male replacement is a relatively infrequent demographic event that can have a profound effect on both the composition and size of the social group. Here, we report such a case and the consequences for home range use and intergroup aggression. Between June 2008 and August 2010, we periodically followed two neighboring groups (Macuco and Rita) in Iguazú National Park, recording daily paths (N = 143) and encounters between the groups (N = 28). We describe the events leading to a change in the male dominance hierarchy in the larger group (Macuco), which resulted in the death or dispersal of all adult males, followed by the succession of a young adult male to the dominant position. This takeover event reduced the numerical advantage in number of males between the two groups, although the ratio of total group sizes remained nearly constant. Following this shift in numerical asymmetry, the degree of escalation of intergroup aggression increased, and we observed reversals in the former intergroup dominance relationship. These changes in behavior during intergroup encounters were associated with changes in the use of overlapping areas. In the 6 months following the takeover, the area of home range overlap doubled, and the formerly dominant group's area of exclusive access was reduced by half. These results suggest that RHPin tufted capuchin monkeys is related to male group size. Furthermore, they highlight the importance of considering rare demographic events in attempts to understand the dynamics of aggression between primate groups.     

Intergroup conflicts among chimpanzees in Taï National Park: lethal violence and the female perspective

Intercommunity aggression in chimpanzees and primitive warfare in humans possess striking similarities, such as the common occurrence of large male coalitions, systematic control of territory boundaries, and lethal attacks on isolated individuals from neighboring groups. However, an important apparent contrast is the absence of recurrent peaceful interactions between neighboring groups of chimpanzees. We observed a remarkable range of behavior in intergroup encounters among three habituated communities of chimpanzees in Taï National Park, Côte d'Ivoire. Lethal attacks are documented in these study groups for the first time, as well as year‐long exchanges of parous adult females and peaceful intergroup visits of mothers with infants. Demographic factors, including group size and number of adult males, are shown to affect the nature of intergroup interactions in ways not considered previously. A reconsideration of the difference in intergroup interactions between eastern and western chimpanzees is proposed including a more important consideration of the female's perspective. The inclusion of the new complexities in intergroup interactions in chimpanzees allows new parallels to be drawn with the evolution of primitive warfare in humans. Am. J. Primatol. 70:519–532, 2008. © 2008 Wiley‐Liss, Inc.     

Intergroup encounters in wild white-faced capuchins (Cebus capucinus)

Wrangham (1980) hypothesized that knowledge of the nature of intergroup encounters is crucial to understanding primate social relationships and social organization. I studied a single social group of wild white-faced capuchins over a period of 26 months and observed 44 encounters between social groups during 3703 hr of observation. All intergroup encounters consisted of predominantly hostile social interactions. However, nonaggressive interactions between males of different social groups occurred in a few cases. Adult males were the sole participants in 39 encounters and the primary participants in all 44 encounters. The alpha male was the most frequent participant. High-ranking females participated aggressively in five encounters, and low-ranking females never participated. There was no stable intergroup dominance hierarchy. I hypothesize that the need for male-male cooperation in intergroup aggression is an important factor influencing the quality of intragroup male-male relationships. Behavior during intergroup encounters is consistent with the idea that intergroup behavior is related to male reproductive strategies, but inconsistent with the idea that intergroup aggression is related to female defense of resources. The possibility that males are “hired guns” (Wrangham, 1980) cannot be ruled out.     

Increased Frequency of Intergroup Encounters in Wild Bonobos (<Emphasis Type="Italic">Pan paniscus</Emphasis>) Around the Yearly Peak in Fruit Abundance at Wamba

Intergroup interactions in primates vary from nonagonistic to severely aggressive. Food resources and fertile females cause intergroup aggression when groups defend resources and mates from other groups. Peaceful intermingling during intergroup encounters is rare but has been reported in several primates, including bonobos (Pan paniscus). Although intergroup encounters in bonobos occur at both nonprovisioned and provisioned sites, provisioning may be one factor responsible for frequent intergroup encounters. We studied intergroup encounters between one bonobo group (PE) and its neighboring groups, one semihabituated and two habituated groups, under nonprovisioned conditions in 2010–2015 at Wamba, Democratic Republic of Congo. We examined whether fruit abundance and females with sexual swellings influenced encounter frequency. PE group encountered the other groups on 7.1 days (mean, range: 0–19) per month. Up to four different groups met simultaneously at one location. Encounter frequency was highest around the yearly peak in fruit abundance, suggesting that reduced food competition is linked to increased encounter frequency. During periods of relatively low fruit abundance, the probability of an encounter was higher when a higher number of adult females with maximum sexual swellings were present, suggesting that the attractiveness of females with sexual swellings promoted group encounters during periods of relatively low fruit abundance. These findings suggest that both competition for food and the availability of females with sexual swellings influence encounter frequency in bonobos.     

Interactions between overlapping multimale groups of black and white colobus monkeys (Colobus guereza) in the Kakamega Forest,Kenya

Sixteen out of 18 groups of black and white colobus monkeys, or guerezas (Colobus guereza), observed in the Kakamega Forest, Kenya, included more than one adult male. Each group overlapped in its home range with 4–7 other groups, and no group appeared to have exclusive access to any part of its home range. Groups were engaged in intergroup encounters one-quarter of observation time. Encounters often occurred around preferred feeding sites as different groups were attracted to such sites in their overlapping home ranges. Wins and losses during encounters were not dependent on location and a null model suggested that groups were not increasing their encounter rate to defend boundaries, further demonstrating a lack of territoriality. Although guerezas have repeatedly been described as a territorial species living in one-male groups, nonterritorial multimale groups are common in continuous forests. Territorial one-male groups may be usual in narrow riparian forests where resources are limiting, groups are small, and defendability is high, but such organization cannot be regarded as typical of the species. Habitat affects group size, as well as the potential for territoriality, and group size determines the number of adult males per group; therefore, classifying groups as one-male or multimale appears to be an artificial dichotomy. © 1996 Wiley-Liss, Inc.     

Intergroup affiliative interactions and intergroup transfer of young male Japanese macaques (Macaca fuscata)

The social interactions between young male Japanese macaques (Macaca fuscata) and members of two adjacent groups were studied. Young males usually associated with members of a single group. Although some young males occasionally interacted with members of the neighboring group, the frequency of their intergroup affiliative interactions was much lower than that of their intragroup interactions. The intergroup affiliative interactions were less symmetrical than the intragroup interactions. Three- or four-year-old males who remained in their natal group interacted with males of the neighboring group, whereas males over 5 years old did not. Young males revealed a dramatic change in their association partners from males in one group to those in another during the course of their intergroup transfer. Males who remained in their natal group did not attempt to interact with females of the neighboring group. In contrast, males who had transferred to a non-natal group interacted with females in their natal group. It is suggested that intergroup affiliative interactions and intergroup transfer of young male macaques are influenced by close associations between males. The immediate motivation for transfer of young natal macaques may be some attraction to males outside their group rather than sexual attraction to unfamiliar females.     

Intergroup encounters in wild moor macaques (<Emphasis Type="Italic">Macaca maurus</Emphasis>)

We studied intergroup encounters among moor macaques at the Karaenta Nature Reserve, South Sulawesi, Indonesia. Group B has been observed on the basis of individual identification since 1988. We analyzed 85 encounters between members of Group B and members of neighboring groups from September 1990 to November 1998. The average frequency of intergroup encounters was 0.035/hour. Neither the presence of females in estrus nor rainfall had an effect on encounter frequency. Behaviors of moor macaques during intergroup encounters differed from those of Japanese macaques. In moor macaques, no intergroup interactions with body contact were observed during encounters, and females never directed aggression toward members of different groups. The present study did not confirm the prediction of the model ofvan Schaik (1989). Extension of the existing models is required to explain the difference in female dominance styles among macaques by socioecological factors.     

Intergroup Relationships in Western Black-and-White Colobus, <Emphasis Type="Italic">Colobus polykomos polykomos</Emphasis>

We investigated patterns of intergroup relationships in western black-and-white colobus, Colobus polykomos, in Taï National Park, Côte d'Ivoire, between 1993 and 1999. They live in one-male multifemale units, and demonstrate male dispersal and occasional dispersal by females. Solitary males and all-male bands are absent or very rare. Our aim was to investigate the function of female and male aggression during intergroup interactions. The species is particularly interesting because, in contrast to predictions from socioecological models, female aggression occurs during intergroup interactions in combination with female dispersal. Home ranges of neighboring groups overlapped considerably and groups lacked an area of exclusive access. Intergroup interactions occurred once every 6.6 observation days. Encounters were either peaceful (12%), or involved displays and threats (25%) or chases and fights (63%). Females interacted in 74% and males in 98% of aggressive intergroup encounters. We found little to no indication that male and female aggression correlated with the presence of food, importance of a location, or presence of infants or receptive females. However, females were more often aggressive during the months when the group depended strongly on seeds from Pentaclethra macrophylla. We also observed forays by males to other groups. Forays occurred on average once every 20 observation days. In 75% of the forays, the intruding male chased members of the target group. In 25% of the forays 1–3 females joined their male but females never attacked the target group. Our main study group was the target of such forays significantly more often when young infants were present in the group than when not. We conclude that female aggression between groups was related to food procurement and that male forays might be related to infanticide.     

Non‐territorial Macaques Can Range Like Territorial Gibbons When Partially Provisioned With Food

Human food supplementation can affect components of animal socioecology by altering the abundance and distribution of available food. We studied the effect of food supplementation by comparing the ranging patterns and intergroup interactions of two groups of northern pigtailed macaques (Macaca leonina), a non‐territorial primate species. One group was partially reliant on food provisioning, whereas the other group foraged wild food. We also compared the macaques’ movement with that of a group of white‐handed gibbons (Hylobates lar), a territorial species inhabiting the same site. Home range, core area, and daily path lengths were significantly smaller for the semi‐provisioned group than for the wild‐feeding group. In contrast to wild‐feeding macaques, supplemented macaques showed higher fidelity to home range, core area, and particularly to the region where human food was most accessible and abundant. The relationship of daily path length and home range indicated a low defendability index for wild‐feeding macaques; the higher index for the semi‐provisioned group was consistent with the territorial pattern found in gibbons. Semi‐provisioned macaques showed further traits of territoriality with aggression during intergroup encounters. These findings indicate that human modification of food availability can significantly affect movement patterns and intergroup competition in macaques. The observed ranging dynamics related to food provisioning may decrease the efficiency of macaques as seed dispersers and increase predation on their home range, and thus have important consequences for plant regeneration and animal diversity.     

Impact of forest fragment size on between-group encounters in lion-tailed macaques

Between-group encounters are an obvious outcome of intergroup competition. Between-group encounters in primates range from avoidance to fatally aggressive. The prevailing hypotheses explain such encounters as mate defense strategy by males and resource defense strategy by females. However, the rate and nature of between-group encounters may also be influenced by habitat and demographic characteristics. We studied the effect of forest fragment size on group encounters in lion-tailed macaques in the Western Ghats of southern India. The encounter rate decreased as the fragment size increased. Group density and home range overlap correlated positively with the encounter rate. The aggressive encounters were more in the relatively medium-sized fragment where the observed frequency of between-group encounters was higher than the expected frequency than in the small fragment and the large forest complex. Together, these results indicate a complex pattern of effects of fragment size on between-group encounters in primates.     

The Equivocal Relationship Between Territoriality and Scent Marking in Wild Saddleback Tamarins (<Emphasis Type="Italic">Saguinus fuscicollis</Emphasis>)

Researchers have often assumed that scent marking serves a territorial function in callitrichines, although some controversy exists. To fulfill such a function, scent marks should 1) prevent intrusions, 2) ensure access to feeding resources, 3) enable avoidance of intergroup encounters, or 4) play an important role in the aggressive encounters between groups. We studied 13 saddleback tamarins (Saguinus fuscicollis) belonging to 3 free-ranging groups, which formed mixed-species troops with moustached tamarins (S. mystax) in the Amazonian rain forest of Peru. None of the predictions were confirmed. The tamarins used a border-marking strategy, marking more on the periphery of their territory. However, feeding trees in overlap and encounter areas received more scent marking but were still visited by neighboring groups. Intergroup encounters occurred more often than expected, and scent-marking frequency was not higher during them than when no other group was present. It appears that instead of defending a territory in the classic sense, the tamarins are optimizing signal transmission by depositing their scents where the probability of detection by neighbors is higher. Saddleback tamarins may use shared areas of their home ranges to exchange information with neighboring groups, perhaps regarding reproductive opportunities.     

Role of loud calls in brown howlers,Alouatta fusca

The loud calls of brown howler monkeys were studied during a year at the Santa Genebra Reserve, in southeastern Brazil. The study group emitted roars and barks on a total of 47 occasions, the majority of which (92%) were restricted to intergroup visual encounters. Loud calls were also elicited by the roars of distant groups (6%) and during intragroup agonistic interactions (2%). Intergroup visual encounters (n = 42) occurred predominantly in seldom used quadrats of the study group home range. In these instances, the loud calls were produced chiefly by the adult male alone (69% of cases), while the study group's two adult females joined the male in the remaining cases. Intergroup physical aggression, such as chase and displacement, was observed during 15 encounters (35% of cases). A dawn chorus does not occur in Santa Genebra—the loud calls were heard most frequently in mid-morning and again during mid-afternoon—and they were more abundant during the dry season, when the availability of food (new leaves) in the forest was lower. The data presented here provide some support for the hypothesis that roars of howler adult males are used in assessment of opponents, providing an alternative to energetically expensive chases and fights. However, given the relatively high rate of physical aggression observed during intergroup encounters, a result probably related to the high density of howlers and the consequent high frequency of intergroup encounters observed in this forest (0.7/day), ritualized aggression, in the form of loud calling, is apparently often insufficient to settle disputes. © 1995 Wiley-Liss, Inc.     

Social dynamics of intergroup encounters in the capped langur (Presbytis pileata)

Data from a 15–month field study of the capped langur (Presbytis pileata) in moist deciduous forest in Bangladesh show that during intergroup encounters males respond more aggressively to extra-group males and to the resident males of unfamiliar one-male groups than they do toward familiar males. Lone males followed established one-male groups and attempted to interact with group females. During intergroup encounters males responded to the approach of unfamiliar males with significantly more displays than were given to familiar (frequently encountered) males. The frequency of displays given to approaching groups showed a negative correlation with the frequency of encounters with those groups. In 50% of intergroup encounters males pushed and bit their group females if the females strayed from the immediate proximity of the group male. Further observations suggest that males obtain females that have emigrated from established groups or attempt to interact with them in established onemale groups. Males had a tenure from at least 13 months to at least 26 months, and between 1986 and 1988 no male changes were seen. Capped langur males defended females from other males, but females did not defend resources or participate in intergroup encounters. The implications of this sex difference in behavior during encounters is discussed with regard to ecological models of female-bonded primate groups.     

Social organization of the Alaotran gentle lemur (Hapalemur griseus alaotrensis)

Knowledge of the social organization of lemurs is still limited for most species. Where there is sufficient information, it has been shown that lemur social organization differs in essential points from that of other primates. In the field study reported here, demographic structure and life-history processes were investigated in order to characterize the social organization of the Alaotran gentle lemur (Hapalemur griseus alaotrensis). Data were obtained through captures and observations. Alaotran gentle lemurs were found in small groups of up to nine individuals. Although most groups contained just one breeding female, a substantial proportion of groups (35%) had two breeding females. Therefore, Alaotran gentle lemurs cannot be classed as being organized in monogamous family groups. An extended birth season was found, and groups with two breeding females had significantly higher breeding output per adult than groups with a single adult female. Limited data suggest that females emigrate from their natal group while still subadult, whereas males can stay in the natal group until they are fully grown and disperse as adults. Variability in group composition, significantly higher reproductive output per adult in groups with two breeding females, and delayed dispersal of males suggest that Alaotran gentle lemurs pursue a resource-defense mating strategy, rather than a female-defense mating strategy. The suggestion that extant social lemurs may have evolved from a monogamous system, could explain the differences between lemur social systems and those of other primates.