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Inference by exclusion, or the ability to select a correct course of action by systematically excluding other potential alternatives, is a form of logical inference that allows individuals to solve problems without complete information. Current comparative research shows that several bird, mammal and primate species can find hidden food through inference by exclusion. Yet there is also wide variation in how successful different species are as well as the kinds of sensory information they can use to do so. An important question is therefore why some species are better at engaging in logical inference than others. Here, we investigate the evolution of logical reasoning abilities by comparing strepsirrhine primate species that vary in dietary ecology: frugivorous ruffed lemurs (Varecia spp.) and folivorous Coquerel's sifakas, Propithecus coquereli. Across two studies, we examined their abilities to locate food using direct information versus inference from exclusion and using both visual and auditory information. In study 1, we assessed whether these lemurs could make inferences when full visual and auditory information about the two potential locations of food were provided. In study 2, we then compared their ability to make direct inferences versus inferences by exclusion in both the visual and auditory domains. We found that these lemur species can use visual information to find food, but that only ruffed lemurs were also able to use auditory cues, mirroring differences in the complexity of their wild ecology. We further found that, unlike many anthropoid species tested to date, these strepsirrhine species failed to make inferences by exclusion. These results highlight the importance of natural history in understanding the evolution of logical inference and help reconstruct the deeper phylogeny of primate cognition.

Interspecific competition can strongly influence patterns of space use in animal communities, particularly between closely related species, and may be exacerbated in marginal habitat. This may be important in Madagascar, as lemurs face diminishing resources due to deforestation. We examined the range overlap and spatiotemporal relationships of three species of frugivorous lemur in the fragmented forests of Kianjavato, Madagascar. We conducted simultaneous location and behaviour sampling of black-and-white ruffed lemurs, Varecia variegata, red-fronted lemurs, Eulemur rufifrons, and red-bellied lemurs, Eulemur rubriventer, at two sites over a period of 11 months. We used Doncaster's index of dynamic interaction to investigate the relative amount of time species spent within 30 m and 100 m of each other, compared to the time expected based on random use of location points. All three species showed low core range overlap compared to home range overlap, and while core overlap was higher between interspecific groups than intraspecific groups, the difference was not substantial. Conversely, no spatiotemporal avoidance was observed, and red-fronted lemurs showed positive association (indicating possible attraction) with both red-bellied and ruffed lemurs. These positive spatiotemporal associations may be related to shared resource use in small forests, or predation avoidance strategies. At present, these species may rely more on spatial segregation and niche separation than spatiotemporal avoidance to minimize interspecific competition.

It is well established that social rank in a large group confers a higher adaptive value to a dominant individual relative to others, although there is scant evidence that members of small social groups either have similar social standing or maintain strict dominance. We aimed to determine whether members of small social groups, using the southern bamboo lemur, Hapalemur meridionalis, as a model, gain rank-related benefits. We first established a dominance hierarchy through a network-based analysis of win–loss interactions, which showed that adult females maintained social dominance within their groups, similar to many strepsirrhine species. To address whether dominant individuals gained rank-related benefits, we then explored how social dynamics may permit access to resting huddles, which provide a physiological benefit. Social thermoregulation, i.e. huddling, is a behavioural energy conservation mechanism, and among many mammals is a direct response to decreasing ambient temperatures. As such, huddling behaviour may have evolved among social animals because of its potential direct and indirect benefits. To examine the effect of dominance rank within small social groups on huddling inclusion, we used generalized linear mixed-effects models to predict the likelihood of huddling occurring during resting bouts from climatic (e.g. temperature, precipitation), social (e.g. affiliation, dominance rank, grooming) and reproductive (e.g. access, infant protection) variables. We found that lower temperatures, especially during shorter resting bouts, increased the likelihood of huddling. Grooming between partners with a high discrepancy in rank increased huddling. Additionally, huddling increased during the reproductive season, potentially offering greater opportunity for males to gain favour with sexually receptive females, and when new-borns were present, providing essential thermal maintenance and potential antipredator protection to infants. Together, our results suggest that even in small social groups, females gain rank-related benefits by controlling access to huddles, i.e. the intrinsic benefits of social thermoregulation.

Resting site selection can have important effects on the behaviour and fitness of organisms. The maintenance of optimal body temperatures (Tb) when faced with environmental variables has often been attributed to either specific microhabitat rest site characteristics or to behavioural strategies. Among many small group-living endotherms, social thermoregulation (i.e. huddling) is utilized as an energy conservation mechanism at low ambient temperatures (Ta), thus decreasing the metabolic cost of maintaining Tb. Although unusual among primates, lemurs maintain a low metabolic rate and exhibit a diversity of thermoregulatory strategies; however, objective Tb measurements have thus far been limited to small-bodied lemurs (e.g. Cheirogaleids). As such, we sought to determine whether a medium-sized lemur model, the southern bamboo lemur, Hapalemur meridionalis, would maintain thermoregulation through microhabitat rest site selection, huddling behaviour, or potentially both strategies. Within a degraded littoral forest fragment in southeast Madagascar, we conducted full-day focal observations on three groups of H. meridionalis between January and December 2013. Adult individuals were collared with data-loggers that collected instantaneous skin temperature Tsk (°C). We calculated the mean Tsk of the focal individual during each resting bout, and the proportional rate of huddling between the focal individual and conspecifics. In addition, we recorded all resting sites utilized for at least 15 min and collected standard tree characteristics. We fitted linear mixed-effects models to determine the thermoregulatory combined effect of specific resting site characteristics, huddling behaviour and environmental variables on Tsk. Our results showed that lemurs selected tree sites with larger diameter at breast height; however, huddling was most predictive of increasing Tsk whereas resting site characteristics were not included in the best-fit model. It is possible that microhabitat rest site selection is not significant in a degraded forest as the potential environmental buffering is limited; thus, thermoregulatory mechanisms are probably best served by behavioural strategies, i.e. social huddling.

Female social dominance over males can only be found in a small number of mammalian species, but is unusually concentrated among Malagasy lemurs. Three major hypotheses are currently discussed to explain this phenomenon, namely the energy conservation hypothesis, sleeping site hypothesis and ancestral lemur condition hypothesis. Since proximate determinants of female dominance have rarely been studied, this study aimed to investigate the influence of factors connected to these hypotheses, focusing on sex-specific differences in energy requirements and group composition in two closely related nocturnal lemur species. More specifically, the effects of species, season and age on agonistic behaviour and the expression of female dominance were tested, while the effects of individuality, body mass, breeding experience and habituation were controlled. Seasonal variations in intersexual dominance relationships were investigated in captivity in grey mouse lemurs, Microcebus murinus , a prominent female-dominant species, and Goodman's mouse lemurs, Microcebus lehilahytsara , whose agonistic behaviour was studied for the first time. Data were collected during a series of encounter experiments between one male and one female (15 dyads of M. murinus and nine of M. lehilahytsara ) during the reproductive and nonreproductive seasons. Moderate female dominance was expressed in both species with females winning the majority of conflicts year round, independently of context. However, effects of season and species were found in conflict rates, in the probability for females to win conflicts, and in the number of dominant females. Moreover, the age difference between dyad partners and the breeding experience of females influenced whether conflicts were decided in favour of males or females. It can be concluded that female dominance probably represents an ancestral trait in mouse lemurs and it is proposed that its evolution might have been driven by sex-specific energetic constraints prevailing in the species-specific ancestral habitats, and may moreover be influenced by the species-specific social organization.

Latrine behaviour is the repeated use of specific sites for defecation/urination, and is common among most mammals, including carnivores, herbivores, marsupials and rodents. While rare among primates, latrine use has been observed among some lemurs. It has been hypothesized that group-living primates may use latrines to maintain intergroup spacing (i.e. territorial defence) and for female advertisement of sexual condition. To test these, we conducted focal follows of three neighbouring southern bamboo lemur, Hapalemur meridionalis, groups in Mandena littoral forest of southeast Madagascar. From January to December 2013, we recorded all occurrences of latrine behaviour and characterized latrine sites to determine what factors influenced returning to specific latrines. Additionally, we attempted to elucidate the functional role of scent marking at latrines. We assessed the degree of home range overlap between neighbouring groups, and recorded intergroup aggression. Overall, latrines were almost exclusively visually conspicuous sites and located in the core areas of group home ranges. Best-fit models indicated that multiply visited latrines occurred more often in core areas, and were influenced by both sexes. Glandular scent marking at latrine sites was driven by males, and occurred more during the nonmating season. Males overmarked female scent-marks less often during the mating season and more often when younger males were likely to disperse. Thus, overmarking at latrine sites may function as a mate-guarding strategy to deter new males. Latrine use supports the energy frugality hypothesis, which proposes that lemur social systems, known for female social dominance and low rates of agonism, evolved as responses to the low productivity of Malagasy forests. The deposition of olfactory cues (i.e. faeces, urine, glandular secretions) at visually conspicuous sites may convey information to neighbouring conspecifics, thus reducing the need for intergroup agonism. Overall, latrine behaviour acts as a multimodal means of intergroup communication.

Vocal exchanges are predicted to serve a social bonding function by allowing conspecifics to ‘groom-at-a-distance’. If vocalizations play a role in bonding, then they should be mainly exchanged between the socially bonded group members, and thus display high social selectivity that characterizes other affiliative behaviours such as grooming. However, whether or not vocal exchanges are driven by social bonds remains unclear. We investigated vocal selectivity by studying the relationships between contact-calling networks and grooming networks in multiple free-ranging groups of ringtailed lemurs, Lemur catta. Lemur grooming interactions were socially selective and were directed towards only some of their group members. However, their vocal exchanges displayed even higher levels of social selectivity. Instead of exchanging vocalizations with each group member they groomed, lemurs reserved their vocal responses mainly for the group members whom they had frequently groomed. We tested this vocal selectivity through a playback experiment in which we presented lemurs' calls to their group. Lemurs responded only to the playbacks of the conspecifics whose calls they had responded to while free-ranging, confirming that selective vocal responses do not depend on proximal (i.e. visual or olfactory) cues from the vocalizing lemur. These robust relationships between grooming and contact-calling networks in lemurs, a species that lives in small groups where grooming frequency reflects bond strength, demonstrates that vocal exchanges indicate the strong social bonds between conspecifics. Contact calls may serve a bonding function in social species by allowing the strongly bonded group members to groom-at-a-distance when they are separated from each other.

Our understanding of chemical signals in mammals derives principally from studies in which researchers examine signal structure or function within a single species. Despite the unique information to be gained from applying comparable methods across multiple species, comparative studies of chemical signals are extremely limited. Here, we review the available literature on the evolution of chemosignals in male and female strepsirrhine primates (galagos, lorises and lemurs), all of which rely heavily on chemical communication. We draw from a few case studies, but focus our review on two comparative studies. In one, researchers examined the volatile chemical composition of urinary signals across 12 species representing most families within Strepsirrhini, including six 'urine-marking' species and six glandular or 'nonurine-marking' species. In the other, researchers examined the volatile chemical composition of glandular signals in eight Eulemur species differing in social or dominance structure. We highlight five findings. (1) Regardless of the scent source, chemical profiles differ substantially between species, providing reliable species 'scent signatures'. None the less, (2) urine markers express more compounds and have more distinguishable species scent signatures in their urine than do nonurine markers, suggesting specialization of function. Within Eulemur (3) chemical richness is greater in multimale-multifemale species than in pair-bonded species. Moreover, (4) whereas chemical richness of male signals is greater in sexually codominant species, chemical richness of female signals is greater in female-dominant species. Together, the findings from both comparative studies, coupled with case studies, suggest that signal richness is linked to some aspect of the focal species' socioecology. Lastly, (5) regardless of the scent source, strepsirrhine chemosignals evolve gradually over time, but at fast rates and homogeneously within different lineages. Comparative studies reveal patterns that cannot be detected from the single-species approach and are therefore critical for providing new insight into the function and evolution of olfactory signals.

As they grow, young individuals can use both social and individual learning strategies to develop species-typical feeding ecology, and the utility of these strategies may vary phylogenetically and with environmental stability. Focused learning from mothers and other group members is critical in monkeys, with behaviours such as co-feeding playing strong roles in determining postweaning survival. While adult lemurs are capable of social learning, it is unknown how social information is incorporated during the development of feeding or what social learning strategies are used in this process. Here we evaluate the use of social learning behaviours and the potential for social learning in young ringtailed lemurs, Lemur catta, at the Beza Mahafaly Special Reserve, Madagascar. We show that infant and juvenile ringtailed lemurs use basic and generalized stimulus enhancement that occurs through behavioural synchrony with older nearest neighbours. More focused co-feeding occurred at low levels, and many of the social learning behaviours observed in the other social primate taxa were absent. High levels of individual exploration also contributed to learning, evidenced through high dietary diversity in juveniles relative to other group members. Our observations are consistent with the idea that simple social learning rules are responsible for the development of ecological complexity in many generalist vertebrate species, and that more complicated learning behaviours may not be necessary to learn complex and varied diets.

During foraging, animals have to balance the risk of predation with the energy gain. The amount of risk animals take for a given resource depends on their energy budget but is expected also to vary between individuals of different personality types. We tested whether individuals of free-ranging grey mouse lemurs, Microcebus murinus, forage risk-sensitively and are consistent in their risk-taking behaviour. Furthermore, we tested whether boldness towards a novel object predicts risk taking in a foraging task. In a field experiment, we simulated low and high predation risk at artificial feeding sites. During focal platform observations, we quantified behaviours related to exploration and feeding for 36 individuals. Furthermore, we used a novel object test to quantify variation in boldness for 22 of these individuals. As predicted, grey mouse lemurs foraged risk-sensitively indicated by longer latencies to enter a feeding platform and to start feeding as well as by relatively longer feeding time compared to nonfeeding in high-risk situations. Individual differences in risk taking were repeatable and repeatability increased with increasing risk. Individual plasticity was higher for low-risk individuals providing field evidence for coping styles. There was no relationship between individual body condition and risk-taking behaviour. Finally, boldness measured in a novel object test was correlated with risk taking in a foraging task, providing a rare ecological validation for this personality trait. These results suggest that intrinsic individual differences in boldness need to be considered as an important source of variation when testing predictions of risk-sensitive foraging using optimality approaches.

Many haplorhine primates flexibly exploit social cues when competing for food. Whether strepsirrhine primates possess similar abilities is unknown. To explore the phylogenetic origins of such skills among primates, we tested ringtailed lemurs, Lemur catta, for their ability to exploit social cues while competing for food. We found that in two contexts ringtailed lemurs spontaneously approached food out of their competitor’s view. To assess whether these skills are related to the relatively complex social structure seen in ringtailed lemurs or shared more broadly across a range of strepsirrhines, we then compared ringtailed lemurs to three lemur species with less complex societies in the same food competition task (N ¼ 50 lemurs). Although all species skilfully avoided food proximate to a competitor in a pretest, only ringtailed lemurs performed above chance in the food competition task that required subjects to avoid food that an experimenter was facing in favour of one that he was not facing. We also compared all four species in a noncompetitive gaze-following task. Ringtailed lemurs were again the only species that looked up more frequently when an experimenter gazed into space than when an experimenter gazed forward (although at relatively low frequencies). These results are consistent with the hypothesis that ringtailed lemurs have undergone convergent social-cognitive evolution with haplorhines, possibly as an adaptation for living in the largest and most complex social groups among strepsirrhines. Results are discussed in terms of lemur cognitive evolution as well as the social intelligence hypothesis. 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

To enhance the fitness benefits of social and sexual interaction, animals should be able to decipher information about the genetic makeup of conspecifics. The use of relative criteria to estimate genetic relatedness could facilitate nepotism or inbreeding avoidance, and the use of absolute criteria to estimate genetic quality could help identify the fittest competitor or the best mate. For animals to process trade-offs between relatedness and quality, however, both relative and absolute genetic information must be concurrently available and detectable by conspecifics. Although there is increasing evidence to suggest that animals make genetically informed decisions about their partners, and may even process trade-offs, we understand relatively little about the sensory mechanisms informing these decisions. In previous analyses of the olfactory signals of ringtailed lemurs, Lemur catta, we showed that both scrotal and labial secretions seasonally encode chemical information about (1) pairwise genetic relatedness, within and between the sexes, and (2) individual heterozygosity. Here, using a signaller–receiver paradigm, we conducted behavioural bioassays to test whether male and female lemurs are sensitive to these olfactory sources of genetic information in unfamiliar conspecifics. As the lemurs discriminated conspecific glandular secretions by pairwise relatedness and individual heterozygosity, volatile olfactory signals can be used by both sexes to concurrently process relative and absolute genetic information about conspecifics. Beyond supporting an olfactory mechanism of kin discrimination and mate choice in a primate, we suggest that animals could use olfactory processing to trade off between selection for the most compatible partner versus the most genetically diverse partner.

Animals spend a substantial proportion of their lives resting and consequently the choice of a sleeping site can dramatically affect an individual's fitness. Sleeping sites have been implicated in predator defence and thermoregulation and their distribution can affect breeding and social systems in small mammals. Sleeping sites may constitute a limiting resource for females which experience energetic constraints to breeding and require shelter for their young. Despite the potential importance of sleeping sites, exhaustive studies of the factors determining their usage patterns are limited to a small number of mammal groups. We investigated how seasonal changes in temperature or the presence of young shape sleeping site usage patterns in a small primate, the grey mouse lemur, Microcebus murinus. Females preferred tree holes over nests and open sites and the usage duration of a particular tree hole site was affected by the physical characteristics likely to affect its insulation properties. Furthermore, climate variables strongly affected sleeping site choices and nests were chosen more often than tree holes during the wet season. However, when young were present preferences shifted back to tree holes. Preferred tree species used as sleeping sites as well as the properties of tree holes were rare among trees in the study area suggesting that sleeping sites may indeed be a limiting resource for female grey mouse lemurs. Our results suggest that in the study species sleeping site choices are governed by thermoregulatory considerations and their limited availability could also account for the social grouping.

Three brown lemurs, Eulemur fulvus, and two black lemurs, Eulemur macaco, were trained to select consistently the photograph of the face of a known individual (KI: belonging to the same social group) when it was presented simultaneously with a photograph of the face of an unfamiliar individual (UI: belonging to another social group). After the learning phase, the subjects were presented with new pairs of photographs (KI versus UI: photographs that were not used in the learning phase), the same pairs presented in different associations, and finally pairs of photographs that were completely novel (50 different pairs). All the subjects selected the KI significantly more often than the UI under all conditions. Additional tests showed that the subjects preferentially selected photographs of a UI belonging to their own species versus a UI belonging to the other species. No preference was observed when the subjects were presented with two KI or with their own photograph associated with a UI. These results reveal that the face contains information allowing lemurs to discriminate familiar individuals from unfamiliar ones.

Among primates, only two lemur genera, Eulemur and Hapalemur, and a population of the platyrrhine Aotus azarai are known to be cathemeral (i.e. show a mixture of daytime and night-time activity). Given the rarity of this phenomenon in primates except for Malagasy lemurs, its proximate and ultimate factors are still debated. The adaptive reasons for this apparently odd lifestyle are mainly based on four not mutually exclusive hypotheses: thermoregulatory benefits, antipredator strategy, competition avoidance and metabolic dietary-related needs. However, little effort has been made to tease apart proximate cues from potential ultimate factors in the multivariate context of activity correlates. To investigate these hypotheses, we compared the year-round cathemeral activity of two groups of Eulemur collaris and one group of hybrids E. collaris × Eulemur fulvus rufus in a humid littoral and in a dry gallery forest of southern Madagascar. Data were collected using a 5 min instantaneous method, with sampling equally distributed between day and night. We weighted the different effects of proximate and ultimate factors via the ANCOVA analysis using as the dependent variable the ratio between diurnal and nocturnal activity. Photoperiodic changes and nocturnal luminosity were the two proximate factors that accounted for most of the variability at the two sites. Diet quality was the only ultimate factor that had a significant effect on the diurnality index of the two lemur populations, suggesting a role of metabolic dietary-related needs in determining cathemeral activity in these lemurs.

Social grooming is a commonly observed affiliative behaviour in primates. Grooming has been suggested to represent a service in a biological marketplace, exchanged either for grooming or for other social commodities or services. Accordingly, grooming is predicted to be approximately reciprocated within a dyad when no other services are being exchanged, but it should be more asymmetrical if partners have different quantities of other services to offer. We analysed 412 grooming bouts observed in four groups of free-ranging redfronted lemurs to test this prediction. Grooming in this species seems to take place in a highly reciprocal manner because partners usually alternate in the roles of groomer and gromee within a grooming bout. However, within dyads there were asymmetries in the duration of grooming given and received. In both sexes, more grooming was directed from low-ranking towards high-ranking individuals than vice versa, and in males this asymmetry became more pronounced as the number of subordinates per group increased. Grooming in bisexual dyads was generally skewed in favour of males, but patterns of grooming between the sexes were less clear than within the sexes. In addition, aggression occurred at high frequencies between classes of individuals that were characterized by nonreciprocal grooming, suggesting that grooming may serve as a means to reduce aggression in dyads with a high potential for conflicts. Taken together, our results indicate that a strict reciprocation of grooming can be offset by power differentials between partners, where grooming appears to be traded by subordinates in exchange for the tolerance of dominants.

Transitive Inference is a form of deductive reasoning that has been suggested as one cognitive mechanism by which animals could learn the many relationships within their group’s dominance hierarchy. This process thus bears relevance to the social intelligence hypothesis which posits evolutionary links between various forms of social and nonsocial cognition. Recent evidence corroborates the link between social complexity and transitive inference and indicates that highly social animals may show superior transitive reasoning even in nonsocial contexts. We examined the relationship between social complexity and transitive inference in two species of prosimians, a group of primates that diverged from the common ancestor of monkeys, apes, and humans over 50 million years ago. In Experiment 1, highly social ring-tailed lemurs, Lemur catta, outperformed the less social mongoose lemurs, Eulemur mongoz, in tests of transitive inference and showed more robust representations of the underlying ordinal relationships between the stimuli. In Experiment 2, after training under a correction procedure that emphasized the underlying linear dimension of the series, both species showed similar transitive inference. This finding suggests that the two lemur species differ not in their fundamental ability to make transitive inferences, but rather in their predisposition to mentally organize information along a common underlying dimension. Together, these results support the hypothesis that social complexity is an important selective pressure for the evolution of cognitive abilities relevant to transitive reasoning.

The sensory bases of food detection, food location and food choice in nocturnal primates are poorly understood. Grey mouse lemurs, Microcebus murinus, are omnivorous nocturnal strepsirhines and generally regarded a good model for the most ancestral primate condition. We set up a series of choice experiments in a controlled laboratory environment to investigate the roles of acoustic, olfactory and visual cues and the importance of unimodal versus multimodal cues for prey perception in this species. Subjects in our study were able to find hidden prey better than expected by chance using any of the three sensory modalities tested; that is, any of the cues provided was sufficient and none was indispensably necessary to trigger prey detection. Availability of visual cues alone enabled successful prey detection in >90% of trials. Detection performance increased with the number of modalities available. Taken together, our data identify vision as a key modality for prey detection in captive-born grey mouse lemurs and at the same time stress the role of multimodal information for successful foraging in this nocturnal primate.

The function of olfactory signalling in social species is less well understood than in asocial species. Consequently, we examined olfactory communication in the ringtailed lemur, a socially complex primate that retains a functional vomeronasal organ, has well-developed scent glands and shows a suite of scent-marking behaviour. To assess the information content of different types of scent gland secretions, we decoupled olfactory cues from the visual and behavioural modalities with which scent marking is normally associated. We presented male and female subjects (signal receivers) with a series of choice tests between odours derived from conspecific donors (signal senders) varying by sex, age, social status and reproductive condition. We additionally examined the influence of the receivers' reproductive state and familiarity with the signaller. The reproductive condition, social status and familiarity of senders and receivers affected signal transmission; specifically, male receivers attended most to the odours of conspecifics in breeding condition and to the odours of familiar, dominant animals. By contrast, females varied their responses according to both their own reproductive state and that of the sender. Based on male and female patterns of countermarking, we suggest that scent marking serves a function in intergroup spacing and intrasexual competition for both sexes, as might be expected in a female-dominant species. By contrast, minimal female interest in male odours counters a female mate choice function for scent marking in this species. Nevertheless, scent marks are critical to male–male competition and, therefore, may be subject to sexual selection.

Six brown lemurs and four black lemurs were presented with two stimulus arrays of one and four raisins. Under a reverse-reward contingency, they received the array they did not choose. All subjects showed a strong preference for the larger array and developed a strong side preference bias. When a large-or-none reward contingency was applied (i.e. no reward followed the choice of the larger array, but this array was given for the choice of the smaller array), six of the 10 subjects overcame their side bias and learned to select the smaller array. When a correction procedure was added, all the remaining subjects mastered the task. Performance was maintained when the original reverse-reward contingency was rerun, and when novel array pairs were presented. Several months after the study, six subjects retained a significant preference for choosing the smaller of the two arrays. The results demonstrate a form of self-control in two prosimian species.

In group-living species, theoretical considerations indicate the existence of a fundamental conflict of interest between the sexes over the adult sex ratio within groups. Females may derive certain benefits from living with many males. Males, in contrast, should generally try to monopolize access to a group of females. Which sex ultimately controls adult group sex ratio is poorly known. We examined this conflict between the sexes in redfronted lemurs, Malagasy primates characterized by an unusual lack of femalebiased adult sex ratios. Using various demographic and behavioural data from several groups collected over 6 years, we examined (1) the proximate determinants of this unusual sex ratio, (2) the temporal distribution of female fertile phases within groups as a determinant of male monopolization potential, (3) sources of between-group variation in the adult sex ratio, and (4) possible social benefits of the relatively high number of males for both sexes. Birth and mortality rates were not sex biased and males migrated considerably more frequently than females, providing no proximate explanation for the unusual sex ratio. However, certain life history traits (fast maturation, short interbirth intervals) may ultimately play a role because they act to facilitate joint group transfers of male coalitions. Despite a relatively small female group size and an associated high monopolization potential, female oestrous synchrony may prevent the formation of single-male groups. Reduced male group size seems to be the main predictor of take-over rate, and, thus, infanticide risk, suggesting that both sexes may benefit from the high number of coresident males, thereby considerably defusing the conflict of interest between the sexes.

We examined predictions on the proportion of dispersing natal males and females, dispersal distances, the age at dispersal and the potential for inbreeding over a 6-year period in a free-living population of grey mouse lemurs. We used monthly mark–recapture procedures to determine individual locations and interindividual distances. The analysis of seven polymorphic microsatellite markers for 213 (130 males, 83 females) individuals allowed us to estimate relatedness coefficients and kinship relationships. Closely related males ranged further from each other than closely related females and natal males were found further from their potential mothers than were females. Natal males were more likely to disperse from their birth sites than females, although male dispersal was not universal. Male breeding dispersal was detected in half of the long-term observations. Males therefore seem to be the predominant vectors for gene flow between populations and social units. Females usually stayed within one to two home range diameters of their potential mother, facilitating the evolution of cooperative behaviour by kin selection among females. Most dispersal took place before the mating season, indicating an age of less than 7 months for natal dispersal. The analysis of spatiotemporal coexistence revealed the potential for inbreeding in only 3.8% of the potential mother–son dyads, but in 21.9% of the potential father–daughter dyads and in 41.7% of other closely related male–female dyads.

Among pair-living species, which represent a simple form of gregariousness, the degree of cohesion appears to be highly variable, but the mechanisms responsible for the maintenance of cohesiveness have been poorly studied. We present data from long-term behavioural observations of eight pairs of fork-marked lemurs, including year-round data on their sleeping site use and spatial data from simultaneous focal follows of both pair partners, that characterize its social organization as ‘dispersed pairs’. Although pairs were stable over several years, territories of pair partners overlapped almost perfectly and interactions between them were frequent, the cohesiveness of pairs was extremely low. High rates of conflict relative to frequencies of affiliative interactions indicated that avoidance of the pair partner is the key mechanism responsible for the observed pattern of space use. The repeated use of the same predictable food resources during the night, frequent conflicts over food and patterns of vocal communication imply that avoidance of direct feeding competition, together with incomplete knowledge about the pair partner's position, lead to the observed low cohesiveness. The freedom to forage solitarily and the associated lack of information about the pair partner's position found in fork-marked lemurs are in contrast to most group-living species and qualify dispersed pairs as a focus for future studies of models on animal movement decisions. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

We examined genetic consequences of basic predictions of life history and sexual selection theory in a wild population of redfronted lemurs. Because group living in lemurs evolved independently from other primates, and because polygynous lemurs deviate in several sexually selected traits from theoretical predictions, data on genetic correlates of their social and mating systems can make important contributions to studies of convergence in social evolution, but such data are not available from wild populations. We extracted DNA from tissue samples obtained from 59 animals living in Kirindy forest, Madagascar, and examined individual variability at several microsatellite loci and the mitochondrial D-loop. We found that closely related females of a single matriline formed the core of the four main study groups. Virtually all haplotypes of adult males differed from those of coresident females, and many male haplotypes were represented by only one or two individuals. Paternity analyses for infants from groups with detailed behavioural data revealed that a disproportionate share of infants were sired by the central, dominant male of a group, despite promiscuous mating. Extragroup paternities were not detected. The skew in male reproductive success cannot be reconciled with the lack of sexual dimorphism and the even adult sex ratios. We therefore conclude that these group-living lemurs converge with many other primates in sex-specific life history trajectories, including female philopatry and male dispersal, but that the observed skew in male reproductive success makes the apparent lack of adaptation to intrasexual selection in certain behavioural, demographic and morphological traits even more puzzling. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Sexual selection theory predicts that the relative importance of dominance between males for access to females depends on the potential to monopolize oestrous females. We examined the relationship between male dominance, mating behaviour and reproductive success in a promiscuous, nocturnal primate species, the grey mouse lemur, in captivity, to test the predictions derived for different competitive regimes between males. We also investigated the relationship between male age, relatedness between mates and reproductive success. Dominance could be established in the majority of the study groups and dominant males mated more frequently than subdominant males. Dominant males, however, fathered only half of the infants born in the study groups, although in principle the captive conditions allowed males to monopolize mates. Multiple mating was observed or deduced from the paternity data in the majority of groups. For the first time in primates we detected one definite case of multiple paternity. Younger males sired more than half of the offspring. We conclude that contest competition between males is unlikely to be the primary factor predicting the reproductive outcome whereas female choice and sperm competition are likely to be effective in this seasonal breeder.

In group-living Malagasy primates (Lemuriformes), certain demographic and morphological traits deviate both from theoretical expectations derived from sexual selection theory and from patterns in better-known anthropoid primates. Lemurs lack sexual dimorphism in body and canine size and live in relatively small multimale-multifemale groups with, on average, even adult sex ratios, despite a polygynous mating system. In addition, the majority of gregarious lemurs are cathemeral, that is, they are regularly active both day and night. The social system of cathemeral lemurs has been considered an adaptation to their activity pattern. If so, groups should consist of multiple pairs that aggregate during diurnal activity and range separately at night in response to predation and infanticide risk, respectively. Moreover, mating privileges should exist between pair partners. We tested this hypothesis with data collected on two groups of wild redfronted lemurs in western Madagascar during 1023 focal animal hours spanning 4 months including the mating season. In addition, data on spatial relations were collected on 12 nights. We found no differences in group cohesion between day and night and no behavioural evidence for multiple male-female pairs. Instead, one male in each group monopolized social interactions with all females. However, females copulated with all resident males, although most often with the central male. Thus, basic predictions of the cathemerality hypothesis are unsupported. Multiple matings and indications of oestrous synchrony can be viewed as female counterstrategies against infanticide, whereas reproductive strategies of redfronted lemur males remain obscure. Copyright 1999 The Association for the Study of Animal Behaviour.

The study of physiological stress and its context in free-ranging animals provides a means for understanding the challenges found in the natural habitat. Patterns of physiological stress in free-ranging animals have yet to be well characterized. Methodological difficulties in measuring physiological responses in the natural habitat have limited this area of research. In this research, physiological stress in free-ranging ring-tailed lemurs, Lemur catta, was estimated using a steroid-extraction method to measure cortisol levels from female faeces. Ten females were observed across two social groups in southwestern Madagascar during a 5-month period including portions of the annual wet and dry seasons. I used behavioural measures to estimate predation threat, food accessibility and individual dominance status, to determine whether these variables predict faecal cortisol levels. Faecal cortisol levels were relatively high during two distinct periods: one period coincided with late gestation and the other period corresponded with the end of the dry season, when high-intensity antipredatory behaviour and estimates of feeding effort were elevated. In addition, faecal cortisol measures were significantly correlated with dominance indices: high-index individuals had high cortisol values, and low-index individuals had low cortisol values. These results suggest that faecal cortisol measures can be used to assess seasonal and individual differences in adrenal activity in this lemurid primate, and that this measure could provide a means for quantifying physiological stress in free-ranging animals. Copyright 1999 The Association for the Study of Animal Behaviour.

Abstract. The post-conflict behaviour of two species of prosimian primates was recorded to examine the effects of agonistic interactions on the subsequent behaviour of former opponents. A total of 125 dyadic agonistic interactions between adults of both species were randomly selected during observations of two social groups of each species. During the 10 min following each agonistic interaction (post-conflict), all social interactions of one of the opponents with all group members, including the former opponent, were recorded and compared with baseline rates established by matched-control observations. In ringtailed lemurs, L. catta , the probability of affinitive interactions between former opponents was not affected by a preceding conflict. In redfronted lemurs, E. fulvus rufus , rates of affinitive interactions between former opponents were significantly above baseline levels in the first 2 min following a conflict, and former opponents were selectively attracted to each other. These post-conflict reunions may function as reconciliations. Significantly larger proportions of undecided conflicts, low-intensity conflicts and conflicts between related redfronted lemurs were reconciled, and victims of aggression were significantly more likely to initiate reconciliation. Neither species showed evidence of consolation, i.e. significantly increased affinitive contact between victims of aggression and third parties during the post-conflict period. Ringtailed lemurs, which have a clear dominance hierarchy and within-group kinship structure, showed a trend toward an increased probability of renewed conflict with former opponents, but not with other group members, during the post-conflict period. They provide the first documented example of a highly social species that appears to lack behavioural mechanisms to cope with the dispersive effects of intra-group aggression. These results demonstrate that reconciliation is not limited to the relatively large-brained anthropoid primates, that reconciliation is not a necessary consequence of group life, and that the occurrence of reconciliation is not limited to species with formalized dominance relations.

A series of studies is described in which some of the sensory and motor capabilities used by the aye-aye, Daubentonia madagascariensis , in foraging for insect larvae are delineated. Although visual and olfactory cues may be of some aid, they are not necessary for successful location of larvae within woody sources. Rather, the aye-aye gently taps on wood surfaces to determine the location of cavities. Although the aye-aye can accurately locate cavities that contain no larvae or those containing inactive prey, significantly more cavities are opened when they contain active larvae. These observations suggest that this primate uses echolocation or a cutaneous sense to find cavities and can also detect the movements of insect larvae within the cavities.

When a captive Lemur fulvus is habituated to the scent of another L. fulvus by repeatedly presenting it with that individual's scent, and is then presented with the scent of a second individual, the amount of sniffing of the scents increases, indicating that it discriminated between the scents of the two individuals. The two individuals' scents were significantly discriminated in eight of eleven different combinations of scent receiver and pair of scent donors. The two scent donors were always of the same sex and subspecies, and they could be discriminated by members of their own or of another sex or subspecies.

Two captive male Lemur fulvus were presented with scents of conspecific males and females, outside the mating season. Both subjects sniffed male scents significantly more than female scents. Male and female scents did not elicit significantly different amounts of scent marking. None of the responses of either subject suggested any discrimination of sub-species by scent.

Two lemurs ( Lemur catta ) received food reward for each vocalization of certain types emitted during 30-min sessions for 20 days. A light stimulus then was introduced for periods totalling half of each session, and only vocalizations made while the light was off were reinforced. Finally, the conditions were reversed and reward followed vocalizations only during the light-on periods. Both animals showed a moderate increase in responses during the continuous-reinforcement situation. In the discrimination situation (and its reversal) response-rate and latency measures showed appropriate differences in behaviour under the two stimulus conditions. The relation to other studies of animal vocalization and its manipulation by reinforcement is discussed.

Eight problems in manipulation of baited and unbaited objects were given to Tupaia, glis, Galago senegalensis, G. crassicaudatus, Loris tardigradus, Perodicticus potto, Lemur fulvus and L. catta. Loris and G. senegalensis have long bouts of attention and much dependance on hand and eye. They orient rather than manipulate, with little or no manipulation of unbaited objects or objects where the reward is not visible. Tupaia and Lemur have short bouts of attention, relatively great dependance on nose and mouth, and much manipulation of unbaited objects. Perodicticus and G. crassicaudatus are intermediate. The animals' approach to objects is the same as their approach to food. Their understanding of unfamiliar objects is clearly below that of higher primates. Prosimians which depend more on hand and eye are not the most intelligent, but the most narrowly specialized. A tendency to manipulative play at the prosimian level may have preceded advance to simian intelligence.