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PubMed2004

Significance of color, calories, and climate to the visual ecology of catarrhines.

Here we describe correlations among visual ecology and the physiochemical properties of fruits and leaves consumed by four species of catarrhine primate: Cercopithecus ascanius, Colobus guereza, Pan troglodytes, and Piliocolobus badius. Collectively, their diet was diverse, with each species relying on fruits and leaves to different extents. The mean chromaticity of both foods, as perceived by the green-red and yellow-blue signals that catarrhines decode, was distinct from background foliage. However, selection on the basis of color was evident only for leaves. Primates consumed leaves with higher green-red values than the leaves they avoided-sensory mechanism that correlated with key nutritional variables, such as increased protein and reduced toughness. Moreover, the monkeys ingested leaves near dusk, when reddish targets may be more salient. Similar patterns were never observed with respect to edible fruits, the chromaticities of which did not differ from unconsumed fruits or correlate with nutritional properties. We also found that primate biomass is higher in seasonal sites. We conclude that these findings are consistent with the notion that routine trichromatic vision evolved in a context where seasonal folivory was pivotal to survival.

Animal Nutritional Physiological Phenomena↗

PubMed2005

Patterns of male residency and intergroup transfer in gray-cheeked mangabeys (Lophocebus albigena).

We describe the movements and fates of 36 collared gray-cheeked male mangabeys (Lophocebus albigena) that resided in seven social groups in Kibale National Park, Uganda. The male mangabeys were captured, radiotagged, and then contacted regularly over a period of up to 8 years. Individuals varied considerably in how tightly they were associated with their groups. "Central" males were usually found in close spatial association with their own groups, but they sometimes visited others. "Peripheral" males were often found several hundred meters away from their own groups. Most adult males were characterized by repeated intergroup transfers, manifested as "visits" and "dispersals." Visits were transfers that did not result in mating. The visits were brief, and ranged from a few minutes to a few days before the male returned to his previous group, moved on to another group, or returned to solitary life. The term "dispersal" refers to a transfer that results in mating, after which the male remains in the new group. Young males began to drift away from their natal groups in early subadulthood, but the timing of first associations with estrous females in other groups was highly variable. Natal dispersers were generally solitary for a month or more, and at least half moved into nonadjacent groups. Secondary dispersal was common. After they immigrated, adult males remained in a group for a median of 19 months before they emigrated again, with the probability of departure being approximately constant in time. Secondary dispersal was usually made into an adjacent group and lasted less than 7 days. Emigration and immigration were not seasonal, and males emigrated singly and apparently independently; however, immigrations were clumped in time, and male dispersal contributed to considerable heterogeneity of group composition. L. albigena dispersal patterns are intermediate between those described for Papio baboons and forest Cercopithecus, and models that predict demographic consequences of dispersal for baboons can be refined to apply to mangabeys.

Animals↗

PubMed2004

Hardness of cercopithecine foods: implications for the critical function of enamel thickness in exploiting fallback foods.

We evaluate the hardness of foods consumed by sympatric Cercopithecus ascanius (redtail guenons) and Lophocebus albigena (grey-cheeked mangabeys), and consider how selection might operate to influence foraging adaptations. Since L. albigena has among the thickest dental enamel in extant primates and is commonly referred to as a hard-object consumer, we predicted that their diet would be harder than that of the guenon. Data on diet and food hardness (as measured by resistance to puncture and crushing) were collected between June-October of 1997 at Kibale National Park, Uganda, and were compared to similar data collected in Kibale between 1991-1994. Contrary to what we predicted, there was no difference in dietary hardness when the puncture resistance of all fruit consumed by the two species was compared (31 tree species in both study periods). However, in June-October 1997, L. albigena exploited a diet more resistant to puncture and crushing than C. ascanius. This difference is largely explained by the higher percentage of bark and seeds consumed by the L. albigena during this period. We suggest that it is the difference in the mechanical properties of fallback foods during critical periods that may have served as the selective pressure for thick enamel in L. albigena.

Adaptation, Physiological↗

PubMed1991

Kinematics of the cercopithecine foot on arboreal and terrestrial substrates with implications for the interpretation of hominid terrestrial adaptations.

The stereotyped characterizations of quadrupedal foot postures were tested by examining the kinematics of the cercopithecine foot on arboreal and terrestrial supports. Strictly arboreal species were compared with semi-terrestrial species for Cercopithecus, Cercocebus, Lophocebus, and Papio, in semi-natural or experimental settings. Results indicate that the kinematics of the cercopithecine arboreal quadruped differ in degree from stereotypical expectations for an arboreal quadruped. The relatively extended, adducted limb movements of the cercopithecines and the emphasis on the central digit as the functional axis of the foot suggest convergence with terrestrial mammalian cursors, and differ from the platyrrhine or colobine arboreal quadruped. The characteristics of the quadrupedal terrestrial primate foot contrast with the very unique pattern seen in the hominid foot. These contrasts provide a new perspective from which to interpret the hominid adaptation, in which the functional axis has remained fixed between the first and second digits. This pattern differs from virtually all other terrestrial mammals. The influence of bipedalism on this functional pattern is examined.

Animals↗

PubMed1992

Erosive arthritis and spondyloarthropathy in Old World primates.

Presence of spine and sacroiliac involvement and the nature and distribution of the erosive lesions allow definitive diagnosis of spondyloarthropathy. Thus, spondyloarthropathy was identified in Theropithecus, Papio, Cercopithecus, Macaca, Colobus, Presbytis, and Hylobates. Only monarticular erosive disease was present in prosimians, precluding a diagnosis of spondyloarthropathy for that group. The distribution of erosive disease and axial joint involvement in 1,349 non-prosimian Old World primates is quite characteristic of that noted in human psoriatic arthritis. While Reiter's syndrome must also be considered, the histologic appearance of skin lesions in Macaca is characteristic of psoriasis. Evidence of spondyloarthropathy abounds in the literature of primate skeletal disease. Environmentally based contagions may be important in the pathophysiology of spondyloarthropathy. The wide geographic distribution of the phenomena in monkeys suggests a "panendemic," with limited individual susceptibility (compared to that noted in gorillas and chimpanzees). Identical occurrence of erosive arthritis/spondyloarthropathy in free-ranging and artificially restrained animals suggests that spondyloarthropathy can validly be studied in artificially restrained populations. This perspective should allow application of human therapeutic approaches to and perhaps improve the quality of life for artificially restrained, afflicted individuals.

Animals↗

PubMed1993

Facial anatomy of Victoriapithecus and its relevance to the ancestral cranial morphology of Old World monkeys and apes.

Recently discovered craniofacial fossils of the middle Miocene cercopithecoid Victoriapithecus are described. The frontal, zygomatic, maxilla, and premaxilla anatomy differ from the previously proposed colobine-like ancestral cercopithecoid morphotype in several significant respects. This morphotype was based on the assumption that features held in common by subordinate hominoid and cercopithecoid morphotypes (Colobinae and Hylobatidae) are primitive for Old World monkeys. Cranial similarities between Victoriapithecus, which represents the sister-group of both colobine and cercopithecine monkeys, and the shorter-snouted Cercopithecinae (Macaca and Cercopithecus) indicate that the last common ancestor of Old World monkeys possessed the following features: a narrow interorbital septum, moderately long snout, moderately long and anteriorly tapering premaxilla, large procumbent upper central incisors set anterior to and with longer roots than lateral incisors, moderately tall face below the orbits, teardrop-shaped nasal aperture of low height and moderate width, and probably long and narrow nasal bones. The Victoriapithecus cranium is also characterized by features not present in modern cercopithecids. These include a deep malar region of the zygomatic and the presence of a frontal trigon due to the occurrence of temporal lines that merge with supraorbital costae close to the midline of each orbit and converge anterior to bregma. These features are interpreted as primitive retentions from the basal catarrhine condition as indicated by the occurrence of these features among primitive catarrhines (Aegyptopithecus) and Miocene hominoids (Afropithecus).

Animals↗

PubMed2002

Gonadal hormones are responsible for maintaining the integrity of spine synapses in the CA1 hippocampal subfield of female nonhuman primates.

It is well established that gonadal hormonal manipulation results in morphologic changes in the rat hippocampus. The great similarities in the hippocampal formation between nonhuman primates and humans, as well as the differences in this structure between humans and rats, led to this investigation of whether hormonal manipulation in female subhuman primates influences pyramidal cell spine density in the CA1 hippocampal subfield, as it does in rats. African green monkeys (Cercopithecus aethiops sabaeus) were ovariectomized, and half of the animals received estrogen replacement therapy. One month later, the monkeys were killed. In the first group of experiments, pyramidal cell spines were analyzed on Golgi-impregnated material taken from the CA1 hippocampal subfield. In the second experiment, unbiased electron microscopic stereologic calculations were performed to estimate the volumetric density of spine synapses in the same hippocampal subfield. Analysis of the Golgi-impregnated material showed that the spine density of CA1 pyramidal cells is much lower in the ovariectomized animals than in ovariectomized and estrogen-replaced monkeys. The unbiased, electron microscopic, stereologic calculation confirmed the light microscopic observation. The volumetric density (number of spine synapses/microm(3)) of spine synapses was significantly lower (43.33%) in the ovariectomized animals than in ovariectomized and estrogen-replaced monkeys. Because the hippocampus is involved in specific mnemonic functions, this observation highlights the importance of hormone replacement therapy in postmenopausal conditions.

Animals↗

PubMed2003

Neurogranin expression by cerebellar neurons in rodents and non-human primates.

Neurogranin (NG) is a brain-specific protein kinase C substrate involved in the regulation of calcium signaling and neuronal plasticity. A rostrocaudal expression profile, with large amounts in telencephalic brain regions and low expression levels in phylogenetically older brain structures, was reported previously. In the cerebellum, expression of NG has not been described. By using immunocytochemistry and in situ hybridization, we found that NG is expressed in the mouse (C57Bl/6), rat (Wistar), and monkey (Cercopithecus aetiops) cerebella. In the mouse cerebellum, Golgi cells were strongly immunoreactive for NG, whereas other cerebellar neurons were devoid of this protein. Cell counts showed 1.6-fold more immunopositive Golgi cells in the hemispheres (61.1 +/- 8.0 cells/mm(2)) than in the vermis (37.5 +/- 3.3 cells/mm(2)). Developmental studies showed detectable NG in the mouse cerebellum as early as on postnatal day 10 (P10). In contrast to the mouse, in the rat cerebellum we found only a few Golgi cells containing NG (hemispheres, 2.4 +/- 0.5 cells/mm(2); vermis, 1.5 +/- 0.3 cells/mm(2)). In the monkey cerebellum, unipolar brush cells, localized in the granular layer, were heavily labeled, whereas Golgi cells were devoid of NG. This study demonstrated that NG is strongly expressed in specific gamma-aminobutyric acidergic neurons in the rodent cerebellum. In addition, NG expression in the primate cerebellum by brush cells, which are excitatory, showed remarkable cell type-specific and species-specific expression patterns of a postsynaptic protein mediating calcium signaling mechanisms.

Animals↗

PubMed2004

Neurogranin is expressed by principal cells but not interneurons in the rodent and monkey neocortex and hippocampus.

As a substrate of protein kinase C (PKC), neurogranin (NG) is involved in the regulation of calcium signaling and activity-dependent plasticity. Recently, we have shown that, in the rodent cerebellum, NG is exclusively expressed by gamma-aminobutyric acidergic Golgi cells, whereas, in the monkey cerebellum, brush cells were the only neuronal population expressing NG (Singec et al. [2003] J. Comp. Neurol. 459:278-289). In the present study, we analyzed the neocortical and hippocampal expression patterns of NG in adult mouse (C57Bl/6), rat (Wistar), and monkey (Cercopithecus aetiops). By using immunocytochemistry and nonradioactive in situ hybridization, we demonstrate strong NG expression by principal cells in different neocortical layers and in the hippocampus by granule cells of the dentate gyrus and pyramidal neurons of CA1-CA3. In contrast, double-labeling experiments in rodents revealed that neocortical and hippocampal interneurons expressing glutamate decarboxylase 67 (GAD67) were consistently devoid of NG. In addition, by using antibodies against parvalbumin, calbindin, and calretinin, we could demonstrate the absence of NG in interneurons of monkey frontal cortex and hippocampus. Together these findings corroborate the idea of different calcium signaling pathways in excitatory and inhibitory cells that may contribute to different modes of synaptic plasticity in these neurons.

Animals↗

PubMed1991

Neuropeptide Y (NPY)-immunoreactive neurons in the primate fascia dentata; occasional coexistence with calcium-binding proteins: a light and electron microscopic study.

Neuropeptide Y (NPY)-containing neurons are known to be highly vulnerable following sustained electrical stimulation in rats and in humans suffering from temporal lobe epilepsy. This has been related to a strong excitatory input. In contrast, there is evidence that neurons containing calcium-binding proteins exhibit a high resistance under experimental seizure and hypoxia conditions. The aim of this study was to determine the coexistence of NPY and calcium-binding proteins in inhibitory neurons of the primate fascia dentata and their synaptic connections. Vibratome sections of hippocampi of African green monkeys (Cercopithecus aethiops) were immunostained with antibodies against NPY, PARV, and CB. A quantitative coexistence study was performed for NPY and PARV on consecutive semithin sections. In contrast to the rodent hippocampus, NPY-immunoreactive neurons were found exclusively in the hilus of fascia dentata with horizontally oriented dendrites which did not extend into the granular and molecular layer. Conversely, PARV-immunoreactive neurons were also present in the granular and inner molecular layer and extended their dendrites far out in the molecular layer and the hilus. Axon terminals immunoreactive for NPY were mostly concentrated in the middle and outer molecular layer and the hilar region and were rare in the granular layer. PARV-immunoreactive boutons were basically restricted to the granular layer where they formed typical baskets. The antibody against calbindin stained almost exclusively granule cells. Coexistence of NPY- and PARV-immunoreactivity was found only in hilar neurons and was rare (9 out of 152 cells analyzed). These results suggest that most NPY-immunoreactive neurons do not contain calcium-binding proteins. NPY-containing neurons exhibited ultrastructural characteristics as described for inhibitory neurons. Their dendrites were only sparsely contacted by mostly asymmetric synaptic terminals, including a very small number of mossy fiber axon terminals. In turn, numerous NPY-immunoreactive axon terminals formed symmetric synapses with spines and dendritic shafts of unlabeled neurons in the middle and outer molecular layer, whereas no contact with granule cell bodies was evident. Thus, we conclude that the vulnerability of NPY-containing inhibitory neurons may be due more to the lack of calcium-binding proteins than to a strong excitatory innervation. As their axons may contribute to the inhibitory control of the major excitatory input from the entorhinal cortex, their loss following overstimulation may play a role in perpetuating hippocampal seizure activity.

Animals↗

PubMed1992

Detection of simian T-lymphotropic virus type I using the polymerase chain reaction.

To develop the polymerase chain reaction (PCR) for the detection of simian T-lymphotropic virus type I (STLV-I) infection, cell lines or peripheral-blood mononuclear cells (PBMC) from 2 non-human primate species [African green monkeys (AGM), Cercopithecus aethiops; baboon, Papio cynocephalus] were evaluated for their STLV-I status using oligonucleotide primer pairs and probes specific for the tax and pol gene regions of the closely related human T-lymphotropic virus type I (HTLV-I). These PCR results were compared with serologic (Western blot assay) and viral culture (p24-antigen capture assay) data. PCR products for both gene regions were detected in established baboon, Japanese macaque and rhesus macaque STLV-I-producing cell lines. STLV-I tax and pol products were also detected in PBMC from 4 of 4 infected AGM and 4 of 4 infected baboons, each of which were also Western-blot-positive and p24-antigen-capture-positive. Of the remaining AGM (n = 7) and baboon (n = 1) which were PCR-negative, each was also Western-blot-negative and p24-antigen-capture-negative. Two seronegative and virus-culture-negative AGM were classified as PCR indeterminate with weak reactivity using tax primers. These primer pairs failed to amplify DNA from uninfected human PBMC, an uninfected human lymphoid cell line, a simian immunodeficiency virus macaque (SIVmac251)-infected cell line and a simian-retrovirus-type-D(SRV-D)-infected cell line. HTLV-II-pol-specific primer pairs failed to amplify DNA from STLV-I-infected cell lines and PBMC from STLV-I-infected monkeys. Further, HTLV-I pol and tax primer pairs successfully amplified RNA from HTLV-I- and STLV-I-infected cell lines by reverse transcriptase (RT)-PCR. We have demonstrated excellent specificity in the detection of STLV-I by PCR using these HTLV-I-derived primers and probes. Additionally, our data suggest that the tax and pol gene regions are conserved between HTLV-I and STLV-I strains found among these diverse species of non-human primates.

Animals↗

PubMed1995

Comparative and functional myology of the prehensile tail in New World monkeys.

The caudal myology of prehensile-tailed monkeys (Cebus apella, Alouatta palliata, Alouatta seniculus, Lagothrix lagotricha, and Ateles paniscus) and nonprehensile-tailed primates (Eulemur fulvus, Aotus trivirgatus, Callithrix jacchus, Pithecia pithecia, Saimiri sciureus, Macaca fascicularis, and Cercopithecus aethiops) was examined and compared in order to identify muscular differences that correlate with osteological features diagnostic of tail prehensility. In addition, electrophysiological stimulation was carried out on different segments of the intertransversarii caudae muscle of an adult spider monkey (Ateles geoffroyi) to assess their action on the prehensile tail. Several important muscular differences characterize the prehensile tail of New World monkeys compared to the nonprehensile tail of other primates. In atelines and Cebus, the mass of extensor caudae lateralis and flexor caudae longus muscles is more uniform along the tail, and their long tendons cross a small number of vertebrae before insertion. Also, prehensile-tailed monkeys, especially atelines, are characterized by well-developed flexor and intertransversarii caudae muscles compared to nonprehensile-tailed primates. Finally, Ateles possesses a bulkier abductor caudae medialis and a more cranial origin for the first segment of intertransversarii caudae than do other prehensile-tailed platyrrhines. These myological differences between nonprehensile-tailed and prehensile-tailed primates, and among prehensile-tailed monkeys, agree with published osteological and behavioral data. Caudal myological similarities and differences found in Cebus and atelines, combined with tail-use data from the literature, support the hypothesis that prehensile tails evolved in parallel in Cebus and atelines.

Animals↗

PubMed1987

Immunization of monkeys with varicella-zoster virus glycoprotein antigens and their response to challenge with simian varicella virus.

African green monkeys (Cercopithecus aethiops) were immunized with three intramuscular injections of gpI, gpII, or gpIII glycoprotein antigens of varicella-zoster virus (VZV). Antibody responses to VZV were determined by enzyme-linked immunosorbent assay (ELISA) and to simian varicella virus (SVV) by immunofluorescence and by serum neutralization assays. Two weeks following the third immunization with VZV glycoproteins, the monkeys were challenged by inoculation of SVV. Antibodies to gpII or gpIII partially prevented infection by SVV, while the presence of antibodies to gpI was ineffective in preventing disease induced by SVV challenge. Factors affecting the immunogenicity of these antigens in this model are discussed.

Animals↗

PubMed1995

Irritable bladder syndrome in an animal model: a continuous monitoring study.

Irritable bladder syndrome (IBS) was induced in four female African green monkeys (Cercopithecus aethiops) by the use of intravesical instillation of acetone. The animals were housed in a modified metabolic cage for continuous micturition monitoring, and two uroflowmeters connected to a remote PC monitored the frequency, voided volumes, and peak flows. Before and after, urea absorption studies and urodynamics were obtained for each animal. Urea absorption increased significantly after acetone instillation and returned to baseline after 4 weeks (26 to 66 to 32%). Intravesical acetone instillation produced marked effects on bladder physiology in the first week. Bladder compliance dropped from a baseline of 10.47 to 0.58 ml/cm H2O. The voiding pattern changed from a normal pattern with a mean voided volume of 17.58 ml into marked increase in frequency and dribbling pattern with few voids (mean = 5.03 ml). Systematic behavioral observations were carried out for 4 hours per day utilizing an observation program on a laptop computer. Activity patterns, attention, sterotypic behaviors, and self-directed activities were recorded for each monkey. The animals demonstrated decreased frequency of activity and increased frequency in self-directed activities (groom, scratch), behaviors consistent with an animal experiencing pain or discomfort. The findings suggested that IBS induction in monkeys is feasible and produces a clinical picture similar to interstitial cystitis in humans. It offers a suitable animal model to enhance the understanding of voiding dysfunction with its neural pathways and to test the different therapeutic modalities to control IBS.

Acetone↗

PubMed1995

Fate of a single dose of 14C-labelled fumonisin B1 in vervet monkeys.

The mycotoxin fumonisin B1 (FB1) was dosed as 14C-labelled FB1, to male vervet monkeys (Cercopithecus aethiops) both by intravenous (i.v.) injection (2 monkeys, dose 1.72 mg [86 kBq]/kg body weight) and by gavage (2 monkeys, dose 6.42 mg [321 kBq]/kg body weight). Excreta were collected over a 24-hr period, whereafter the monkeys were sacrificed and selected organs and contents of the gut collected to determine the distribution of the 14C-label. The bulk of the radioactivity recovered from tissue was found in the liver (mean of 1.92% in i.v.-dosed monkeys; 0.64% in gavage-dosed monkeys). Of the other organs analysed, the following mean amounts of radioactivity were recovered in organs of i.v.- and gavage-dosed monkeys, respectively: muscle, 0.62% and 0.14%; kidney, 0.37% and 0.03%; brain, 0.08% and 0.02%; lung, 0.07% and 0.03%; heart, 0.04% and 0.01%; spleen, 0.02% and < 0.01%; plasma, 0.66% and 0.12%; red blood cells, 0.11% and 0.01%; while a further 68.1% and 64.0% were recovered in excreta, bile, and the gut contents. Analysis of faeces and gut contents showed that radioactivity was due to FB1, its partially hydrolysed metabolites, and trace amounts of the fully hydrolysed aminopentol moiety. Analysis of bile showed an absence of hydrolysis products, indicating that hydrolysis occurred only in the gut, resulting in the removal of the tricarballylic acid moiety at the C14-position. Determination of FB1, levels in plasma following a gavage dose indicated that only limited amounts of FB1 were absorbed, as plasma levels peaked after 1-2 hr with levels below 210 ng/ml.

Animals↗

PubMed1997

Red colobus and Diana monkeys provide mutual protection against predators.

We tested the hypothesis that red colobus monkeys, Procolobus badius and Diana monkeys, Cercopithecus diana in Taï National Park, Ivory Coast, associate to increase safety from predation. We recorded stratum use, exposure and vigilance of each species in the presence and in the absence of the partner species. In the presence of Diana monkeys, red colobus used lower strata more often, were more exposed to the forest floor and looked down less often while foraging. This suggests that red colobus reduce predation pressure from ground predators by associating with Diana. There are several indications that both species are less vulnerable to birds of prey when associated: red colobus looked sideways less often and were more exposed to the front, Diana monkeys used greater heights and were more exposed to the front, to the rear and from above. We also asked whether specific sentinel qualities of Diana monkeys might explain why other sympatric monkey species additionally seek their presence. When groups of various species compositions were approached by an observer, or confronted with an eagle model, Diana monkeys raised the alarm in most cases. Since neither monkey species improves its foraging success when associated, this study shows that predation can both maintain and be the ultimate cause of interspecific associations.Copyright 1997 The Association for the Study of Animal Behaviour

Journal Article↗

PubMed1999

Vocal recognition in the spotted hyaena and its possible implications regarding the evolution of intelligence.

Spotted hyaenas, Crocuta crocuta, are gregarious carnivores whose social lives share much in common with those of cercopithecine primates. We conducted playback experiments to determine whether free-living hyaenas are capable of identifying individual conspecifics on the basis of their long-distance vocalization, the 'whoop'. When prerecorded cub whoops were played to mothers and other breeding females (controls), mothers responded significantly more vigorously to whoops of their own cubs than did controls. We also tested the hypothesis that specific vocal recognition abilities are based on kinship in this species. Listeners that were related to the whooping cub responded more vigorously to recorded vocalizations than did unrelated individuals, with response intensity in some cases increasing directly with the size of the coefficient of relatedness (r). Our final goal was to determine whether control animals in these experiments can recognize third-party social relationships among other group members, an ability demonstrated by vervet monkeys, Cercopithecus aethiops, in similar playback experiments conducted by earlier investigators. In contrast to vervets, control females in the present experiments were no more likely to look at the mother of the whooping cub than at other control females after playback. This suggests that hyaenas may accomplish many of the same social feats as do vervets without possessing the ability to recognize third-party relationships. If confirmed in other domains of hyaena social life, our findings have important implications regarding selection pressures favouring the evolution of intelligence. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2000

Causal knowledge of predators' behaviour in wild Diana monkeys.

Wild Diana monkeys, Cercopithecus diana, of Taï forest, Ivory Coast, are preyed upon by leopards, Panthera pardus, and chimpanzees, Pan troglodytes. These two predators differ in their main hunting tactic and Diana monkeys attempt to avoid predation with two distinct antipredator strategies: conspicuous alarm-calling behaviour to leopards and silent, cryptic behaviour to chimpanzees. However, the Diana monkeys' choice of the appropriate antipredator strategy is complicated by the fact that chimpanzees themselves also fall prey to leopards. Chimpanzees give loud and conspicuous alarm screams when they detect a leopard. When these chimpanzees' leopard alarm calls were played back to different groups of Diana monkeys, in about half of the cases recipients switched from a chimp-specific cryptic response to a leopard-specific conspicuous response, suggesting that some individuals assumed the presence of a leopard. Groups whose home range was in the core area of the resident chimpanzee community were more likely to respond this way than more peripheral groups, indicating between-group differences in semantic knowledge. In a follow-up experiment, the monkeys' understanding of the chimpanzee alarm calls was further assessed with a prime-probe technique. Monkeys were primed with chimpanzee alarm calls and then, 5 min later, tested with leopard growls to see whether they were able to anticipate the presence of a leopard. Results were consistent with the hypothesis that monkeys responding cryptically to chimpanzee alarm calls did so because they were not able to understand the calls' meaning. Data are discussed with respect to three possible cognitive mechanisms, associative learning, specialized learning programmes, and causal reasoning, that could have led to causal knowledge in some individuals but not others. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗