Small-bodied Primates Research Articles

A coati conundrum: how variation in levels of arboreality influences gait mechanics among three musteloid species.

The gait characteristics associated with arboreal locomotion have been frequently discussed in the context of primate evolution, wherein they present as a trio of distinctive features: a diagonal-sequence, diagonal-couplet gait pattern; a protracted arm at forelimb touchdown; and a hindlimb-biased weight support pattern. The same locomotor characteristics have been found in the woolly opossum, a fine-branch arborealist similar in ecology to some small-bodied primates. To further our understanding of the functional link between arboreality and primate-like locomotion, we present comparative data collected in the laboratory for three musteloid taxa. Musteloidea represents an ecologically diverse superfamily spanning numerous locomotor specializations that includes the highly arboreal kinkajou (Potos flavus), mixed arboreal/terrestrial red pandas (Ailurus fulgens) and primarily terrestrial coatis (Nasua narica). This study applies a combined kinetic and kinematic approach to compare the locomotor behaviors of these three musteloid taxa, representing varying degrees of arboreal specialization. We observed highly arboreal kinkajous to share many locomotor traits with primates. In contrast, red pandas (mixed terrestrial/arborealist) showed gait characteristics found in most non-primate mammals. Coatis, however, demonstrated a unique combination of locomotor traits, combining a lateral-sequence, lateral-couplet gait pattern typical of long-legged, highly terrestrial mammals, varying degrees of arm protraction, and a hindlimb-biased weight support pattern typical of most primates and woolly opossums. We conclude that the three gait characteristics traditionally used to describe arboreal walking in primates can occur independently from one another and not necessarily as a suite of interdependent characteristics, a phenomenon that has been reported for some primates.

Energetic costs of feeding in 12 species of small-bodied primates.

There are no comparative, empirical studies of the energetic costs of feeding in mammals. As a result, we lack physiological data to better understand the selection pressures on the mammalian feeding apparatus and the influence of variables such as food geometric and material properties. This study investigates interspecific scaling of the net energetic costs of feeding in relation to body size, jaw-adductor muscle mass and food properties in a sample of 12 non-human primate species ranging in size from 0.08 to 4.2 kg. Net energetic costs during feeding were measured by indirect calorimetry for a variety of pre-cut and whole raw foods varying in geometric and material properties. Net feeding costs were determined in two ways: by subtracting either the initial metabolic rate prior to feeding or subtracting the postprandial metabolic rate. Interspecific scaling relationships were evaluated using pGLS and OLS regression. Net feeding costs scale negatively relative to both body mass and jaw-adductor mass. Large animals incur relatively lower feeding costs indicating that small and large animals experience and solve mechanical challenges in relation to energetics in different ways. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Acclimatizing and training freely viewing marmosets for behavioral and electrophysiological experiments in oculomotor tasks.

The marmoset is a small-bodied primate with behavioral capacities and brain structures comparable to macaque monkeys and humans. Its amenability to modern biotechnological techniques like optogenetics, chemogenetics, and generation of transgenic primates have attracted neuroscientists' attention to use it as a model in neuroscience. In the past decade, several laboratories have been developing and refining tools and techniques for performing behavioral and electrophysiological experiments in this new model. In this regard, we developed a protocol to acclimate the marmoset to sit calmly in a primate chair; a method to calibrate the eye-tracking system while marmosets were freely viewing the screen; and a procedure to map motor field of neurons in the SC in freely viewing marmosets. Using a squeeze-walled transfer box, the animals were acclimatized, and chair trained in less than 4 weeks, much shorter than what other studies reported. Using salient stimuli allowed quick and accurate calibration of the eye-tracking system in untrained freely viewing marmosets. Applying reverse correlation to spiking activity and saccadic eye movements, we were able to map motor field of SC neurons in freely viewing marmosets. These refinements shortened the acclimation period, most likely reduced stress to the subjects, and allowed more efficient eye calibration and motor field mapping in freely viewing marmosets. With a penetration angle of 38 degrees, all 16 channels of the electrode array, that is, all recorded neurons across SC layers, had overlapping visual receptive and motor fields, indicating perpendicular penetration to the SC.

Population genomic structure in Goodman's mouse lemur reveals long-standing separation of Madagascar's Central Highlands and eastern rainforests.

Madagascar's Central Highlands are largely composed of grasslands, interspersed with patches of forest. The historical perspective was that Madagascar's grasslands had anthropogenic origins, but emerging evidence suggests that grasslands were a component of the pre-human Central Highlands vegetation. Consequently, there is now vigorous debate regarding the extent to which these grasslands have expanded due to anthropogenic pressures. Here, we shed light on the temporal dynamics of Madagascar's vegetative composition by conducting a population genomic investigation of Goodman's mouse lemur (Microcebus lehilahytsara; Cheirogaleidae). These small-bodied primates occur both in Madagascar's eastern rainforests and in the Central Highlands, making them a valuable indicator species. Population divergences among forest-dwelling mammals will reflect changes to their habitat, including fragmentation, whereas patterns of post-divergence gene flow can reveal formerly wooded migration corridors. To explore these patterns, we used RADseq data to infer population genetic structure, demographic models of post-divergence gene flow, and population size change through time. The results offer evidence that open habitats are an ancient component of the Central Highlands, and that widespread forest fragmentation occurred naturally during a period of decreased precipitation near the last glacial maximum. Models of gene flow suggest that migration across the Central Highlands has been possible from the Pleistocene through the recent Holocene via riparian corridors. Though our findings support the hypothesis that Central Highland grasslands predate human arrival, we also find evidence for human-mediated population declines. This highlights the extent to which species imminently threatened by human-mediated deforestation may already be vulnerable from paleoclimatic conditions.

The gut microbiome and metabolome of saddleback tamarins (Leontocebus weddelli): Insights into the foraging ecology of a small-bodied primate.

Body mass is a strong predictor of diet and nutritional requirements across a wide range of mammalian taxa. In the case of small-bodied primates, because of their limited gut volume, rapid food passage rate, and high metabolic rate, they are hypothesized to maintain high digestive efficiency by exploiting foods rich in protein, fats, and readily available energy. However, our understanding of the dietary requirements of wild primates is limited because little is known concerning the contributions of their gut microbiome to the breakdown and assimilation of macronutrients and energy. To study how the gut microbiome contributes to the feeding ecology of a small-bodied primate, we analyzed the fecal microbiome composition and metabolome of 22 wild saddleback tamarins (adult body mass 360-390 g) in Northern Bolivia. Samples were analyzed using high-throughput Illumina sequencing of the 16 S rRNA gene V3-V5 regions, coupled with GC-MS metabolomic profiling. Our analysis revealed that the distal microbiome of Leontocebus weddelli is largely dominated by two main bacterial genera: Xylanibacter and Hallella (34.7 ± 14.7 and 22.6 ± 12.4%, respectively). A predictive analysis of functions likely carried out by bacteria in the tamarin gut demonstrated the dominance of membrane transport systems and carbohydrate metabolism as the predominant metabolic pathways. Moreover, given a fecal metabolome composed mainly of glucose, fructose, and lactic acid (21.7 ± 15.9%, 16.5 ± 10.7%, and 6.8 ± 5.5%, respectively), the processing of highly fermentable carbohydrates appears to play a central role in the nutritional ecology of these small-bodied primates. Finally, the results also show a potential influence of environmentally-derived bacteria in colonizing the tamarin gut. These results indicate high energetic turnover in the distal gut of Weddell's saddleback tamarin, likely influenced by dominant bacterial taxa that facilitate dietary dependence on highly digestible carbohydrates present in nectar, plant exudates, and ripe fruits.

Eye Size and Set in Small-Bodied Fossil Primates: A Three-Dimensional Method.

We introduce a new method to geometrically reconstruct eye volume and placement in small-bodied primates based on the three-dimensional contour of the intraorbital surface. We validate it using seven species of living primates, with dry skulls and wet dissections, and test its application on seven species of Paleogene fossils of interest. The method performs well even when the orbit is damaged and incomplete, lacking the postorbital bar and represented only by the orbital floor. Eye volume is an important quantity for anatomic and metabolic reasons, which due to differences in eye set, or position within (or outside) the bony orbit, can be underestimated in living and fossil forms when calculated from aperture diameter. Our Ectopic Index quantifies how much the globe's volume protrudes anteriorly from the aperture. Lemur, Notharctus and Rooneyia resemble anthropoids, with deeply recessed eyes protruding 11%-13%. Galago and Tarsius are the other extreme, at 47%-56%. We argue that a laterally oriented aperture has little to do with line-of-sight in euprimates, as large ectopic eyes can position the cornea to enable a directly forward viewing axis, and soft tissue positions the eyes facing forward in megachiropteran bats, which have unenclosed, open eye sockets. The size and set of virtual eyes reconstructed from 3D cranial models confirm that eyes were large to hypertrophic in Hemiacodon, Necrolemur, Microchoerus, Pseudoloris and Shoshonius, but eye size in Rooneyia may have been underestimated by measuring the aperture, as in Aotus. Anat Rec, 299:1671-1689, 2016. © 2016 Wiley Periodicals, Inc.

Behavior and Ecology of the White-Footed Tamarin (Saguinus Leucopus) in a Fragmented Landscape of Colombia: Small Bodied Primates and Seed Dispersal in Neotropical Forests

Tamarins are small-bodied Neotropical primates that mainly feed on ripe fruits and insects, and supplement their diet with plant exudates, nectar, fungi and vertebrate prey. They are important seed dispersers in Neotropical forests as they are able to disperse a large number of small and medium-sized seeds from parental trees. In this paper, we describe the diet of the white-footed tamarin ( Saguinus leucopus) and its role as seed disperser in a fragmented landscape in Colombia. During a twelve month period, we collected data on activity patterns, ranging behavior and feeding ecology, as well as on habitat-wide forest productivity. S. leucopus fed from >95 plant species and spent 17% of their time feeding. We found a positive relationship between fruit consumption and ripe-fruit availability. Dietary diversity increased during periods of fruit scarcity, when the tamarins fed more on insects and exudates. During periods of fruit scarcity, they relied more heavily on the borders of forest fragments and made occasional incursions into adjacent fragments across a matrix of pastures. They used larger areas and had larger overlapping home ranges during periods of fruit scarcity. We recovered at least 44 species of seeds effectively dispersed by tamarins, including small and medium-sized seeds (range <1–26 mm). Seeds were dispersed up to 500m from parent trees across a wide diversity of habitat types. This study provides further evidence on the important role small-bodied frugivorous primates play in the recovery of forest connectivity and in the maintenance of tropical forest diversity in human-impacted landscapes.

Patterns of quadrupedal locomotion in a vertical clinging and leaping primate (Propithecus coquereli) with implications for understanding the functional demands of primate quadrupedal locomotion.

Many primates exhibit a suite of characteristics that distinguish their quadrupedal gaits from non-primate mammals including the use of a diagonal sequence gait, a relatively protracted humerus at touchdown, and relatively high peak vertical forces on the hindlimbs compared to the forelimbs. These characteristics are thought to have evolved together in early, small-bodied primates possibly in response to the mechanical demands of navigating and foraging in a complex arboreal environment. It remains unclear, however, whether primates that employ quadrupedalism only rarely demonstrate the common primate pattern of quadrupedalism or instead use the common non-primate pattern or an entirely different mechanical pattern from either group. This study compared the kinematics and kinetics of two habitually quadrupedal primates (Lemur catta and Varecia variegata) to those of a dedicated vertical clinger and leaper (Propithecus coquereli) during bouts of quadrupedal walking. All three species employed diagonal sequence gaits almost exclusively, displayed similar degrees of humeral protraction, and exhibited lower vertical peak forces in the forelimbs compared to the hindlimb. From the data in this study, it is possible to reject the idea that P. coquereli uses a non-primate pattern of quadrupedal walking mechanics. Nor do they use an entirely different mechanical pattern from either most primates or most non-primates during quadrupedal locomotion. These findings provide support for the idea that this suite of characteristics is adaptive for the challenges of arboreal locomotion in primates and that these features of primate locomotion may be basal to the order or evolved independently in multiple lineages including indriids. Am J Phys Anthropol 160:644-652, 2016. © 2016 Wiley Periodicals, Inc.

The common marmoset (<i>Callithrix jacchus</i>): a relevant preclinical model of human (auto)immune-mediated inflammatory disease of the brain

Abstract. The increasing prevalence of chronic autoimmune-mediated inflammatory disorders (AIMIDs) in aging human populations creates a high unmet need for safe and effective medications. However, thus far the translation of pathogenic concepts developed in animal models into effective treatments for the patient has been notoriously difficult. The main reason is that currently used mouse-based animal models for the pipeline selection of promising new treatments were insufficiently predictive for clinical success. Regarding the high immunological similarity between human and non-human primates (NHPs), AIMID models in NHPs can help to bridge the translational gap between rodent and man. Here we will review the preclinical relevance of the experimental autoimmune encephalomyelitis (EAE) model in common marmosets (Callithrix jacchus), a small-bodied neotropical primate. EAE is a generic AIMID model projected on the human autoimmune neuro-inflammatory disease multiple sclerosis (MS).

English

Birth palsy, otherwise known as obstetric brachial plexus paralysis (OBPP), is a closed stretch injury to the brachial plexus of nerves during the birth process resulting in varying degree of paralysis and contractures of the upper limb. The study aimed to find out the susceptibility of humans and small-bodied primates to birth palsy. A comparative study on parturition in modern humans, hominoids, hominids, small-bodied primates and great apes was done to determine if the changes in female pelvis and neonatal head and shoulder during human evolution is the real cause for OBPP. During evolution, the morphology of the female pelvis and birth canal changed into a narrow and twisted one and also the size of the fetal head increased. Thus, the narrow and twisted pelvis of the mother, and the relatively large head and broad shoulders of the newborn has made the birthing process of modern human and small bodied primates a precarious fine-tuned act with a very narrow margin for error. This has necessitated proper obstetric care to reduce or even at times obviate the incidence of birth injuries like OBPP. Human evolution has made human babies susceptible to birth palsy and thus is the real cause of birth palsy.

Losing grip: Senescent decline in physical strength in a small-bodied primate in captivity and in the wild

Muscle strength reflects physical functioning, declines at old age and predicts health and survival in humans and laboratory animals. Age-associated muscle deterioration causes loss of strength and may impair fitness of wild animals. However, the effects of age and life-history characteristics on muscle strength in wild animals are unknown. We investigated environment- and sex-specific patterns of physical functioning by measuring grip strength in wild and captive gray mouse lemurs. We expected more pronounced strength senescence in captivity due to condition-dependent, extrinsic mortality found in nature. Males were predicted to be stronger but potentially experience more severe senescence than females as predicted by life history theory. We found similar senescent declines in captive males and females as well as wild females, whereas wild males showed little decline, presumably due to their early mortality. Captive animals were generally weaker and showed earlier declines than wild animals. Unexpectedly, females tended to be stronger than males, especially in the reproductive season. Universal intrinsic mechanisms (e.g. sarcopenia) likely cause the similar patterns of strength loss across settings. The female advantage in muscle strength merits further study; it may follow higher reproductive investment by males, or be an adaptation associated with female social dominance.

Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate

Classic theories of ageing consider extrinsic mortality (EM) a major factor in shaping longevity and ageing, yet most studies of functional ageing focus on species with low EM. This bias may cause overestimation of the influence of senescent declines in performance over condition-dependent mortality on demographic processes across taxa. To simultaneously investigate the roles of functional senescence (FS) and intrinsic, extrinsic and condition-dependent mortality in a species with a high predation risk in nature, we compared age trajectories of body mass (BM) in wild and captive grey mouse lemurs (Microcebus murinus) using longitudinal data (853 individuals followed through adulthood). We found evidence of non-random mortality in both settings. In captivity, the oldest animals showed senescence in their ability to regain lost BM, whereas no evidence of FS was found in the wild. Overall, captive animals lived longer, but a reversed sex bias in lifespan was observed between wild and captive populations. We suggest that even moderately condition-dependent EM may lead to negligible FS in the wild. While high EM may act to reduce the average lifespan, this evolutionary process may be counteracted by the increased fitness of the long-lived, high-quality individuals.

Interactions between social structure, demography, and transmission determine disease persistence in primates.

Catastrophic declines in African great ape populations due to disease outbreaks have been reported in recent years, yet we rarely hear of similar disease impacts for the more solitary Asian great apes, or for smaller primates. We used an age-structured model of different primate social systems to illustrate that interactions between social structure and demography create ‘dynamic constraints’ on the pathogens that can establish and persist in primate host species with different social systems. We showed that this varies by disease transmission mode. Sexually transmitted infections (STIs) require high rates of transmissibility to persist within a primate population. In particular, for a unimale social system, STIs require extremely high rates of transmissibility for persistence, and remain at extremely low prevalence in small primates, but this is less constrained in longer-lived, larger-bodied primates. In contrast, aerosol transmitted infections (ATIs) spread and persist at high prevalence in medium and large primates with moderate transmissibility;, establishment and persistence in small-bodied primates require higher relative rates of transmissibility. Intragroup contact structure – the social network - creates different constraints for different transmission modes, and our model underscores the importance of intragroup contacts on infection prior to intergroup movement in a structured population. When alpha males dominate sexual encounters, the resulting disease transmission dynamics differ from when social interactions are dominated by mother-infant grooming events, for example. This has important repercussions for pathogen spread across populations. Our framework reveals essential social and demographic characteristics of primates that predispose them to different disease risks that will be important for disease management and conservation planning for protected primate populations.

Altitude and Forest Edges Influence the Density and Distribution of Pygmy Tarsiers (Tarsius pumilus)

In this study, we examine how high-altitude ecology and anthropogenic edges relate to the density and distribution of pygmy tarsiers. Pygmy tarsiers (Tarsius pumilus) are extremely small-bodied primates (55 g) that are endemic to high-altitude forest and exhibit several differences from lowland Sulawesian tarsier species. From June to September 2010 and January to March 2012, we conducted a population census of pygmy tarsiers across multiple altitudes. Sampling took place within a 1.2 km(2) area encompassing altitudes of 2,000-2,300 m a.s.l. on Mt. Rore Katimbu in Lore Lindu National Park, central Sulawesi, Indonesia. We observed 22 individuals, with an estimated population density of 92 individuals per 100 ha. These results indicate that pygmy tarsiers live at a lower density than lowland Sulawesian tarsier species. Lower density was associated with decreased resources at higher altitudes, including decreased tree size, tree density, and insect biomass. Within the sample area, we found pygmy tarsiers in only 8 of 24 (33%) quadrats, suggesting a nonrandom distribution that probably overinflated this population density estimate. Pygmy tarsiers exhibited a clumped distribution near anthropogenic edges that were associated with increased insect abundance and biomass. Airborne insects were more abundant along forest edges than within the forest interior, and pygmy tarsiers were observed to forage along edges where there was a higher abundance of Lepidoptera and Orthoptera. Tarsiers may mitigate the decreased availability of insects at high altitudes by adjusting their ranging patterns to remain near forest edges.

Toward a nonhuman primate model of fetal programming: Phenotypic plasticity of the common marmoset fetoplacental complex

Nonhuman primates offer unique opportunities as animal models in the study of developmental programming and the role of the placenta in developmental processes. All primates share fundamental similarities in life history and reproductive biology. Thus, insights gleaned from studies of nonhuman primates have a higher degree of biological salience to human biology than do studies of rodents or agricultural animals. The common marmoset monkey is a small-bodied primate from South America that produces litters of dizygotic fetuses that share a single placental mass. This natural variation allows us to model different intrauterine conditions and associated fetoplacental phenotypes. The marmoset placenta is phenotypically plastic according to litter size. Triplet litters are characterized by low individual fetal weights and significantly more efficient placentas and attendant alterations to the microscopic architecture and endocrine function, thus modeling a nutrient restricted intrauterine environment. Consistent with this model, triplet neonates experience a higher risk of perinatal mortality and an increased likelihood of elevated adult weight. Recent evidence has shown that the intrauterine experience of females has an impact on their own pregnancy outcomes in adulthood: triplet females experience significantly greater pregnancy loss than do twin females. The marmoset monkey thus represents a potential powerful nonhuman primate model of multiple pregnancies, restrictive prenatal experiences, and differential reproductive outcomes in adulthood, which may have important implications for studying the impact of in vitro fertilization on adult reproductive health. It is still too early to determine exactly what developmental pathways lead to this disparity or what specific role the placenta plays; future work on this front will be critical to establish the marmoset as an important model of fetal programming of reproductive function in adulthood and across generations.

Posture does not matter! Paw usage and grasping paw preference in a small-bodied rooting quadrupedal mammal.

BackgroundRecent results in birds, marsupials, rodents and nonhuman primates suggest that phylogeny and ecological factors such as body size, diet and postural habit of a species influence limb usage and the direction and strength of limb laterality. To examine to which extent these findings can be generalised to small-bodied rooting quadrupedal mammals, we studied trees shrews (Tupaia belangeri).Methodology/Principal FindingsWe established a behavioural test battery for examining paw usage comparable to small-bodied primates and tested 36 Tupaia belangeri. We studied paw usage in a natural foraging situation (simple food grasping task) and measured the influence of varying postural demands (triped, biped, cling, sit) on paw preferences by applying a forced-food grasping task similar to other small-bodied primates. Our findings suggest that rooting tree shrews prefer mouth over paw usage to catch food in a natural foraging situation. Moreover, we demonstrated that despite differences in postural demand, tree shrews show a strong and consistent individual paw preference for grasping across different tasks, but no paw preference at a population level.Conclusions/SignificanceTree shrews showed less paw usage than small-bodied quadrupedal and arboreal primates, but the same paw preference. Our results confirm that individual paw preferences remain constant irrespective of postural demand in some small-bodied quadrupedal non primate and primate mammals which do not require fine motoric control for manipulating food items. Our findings suggest that the lack of paw/hand preference for grasping food at a population level is a universal pattern among those species and that the influence of postural demand on manual lateralisation in quadrupeds may have evolved in large-bodied species specialised in fine manipulations of food items.

Fruit availability, frugivore satiation and seed removal in 2 primate‐dispersed tree species

During a mast-fruiting event we investigated spatial variability in fruit availability, consumption, and seed removal at two sympatric tree species, Manilkara bidentata and M. huberi (Sapotaceae) at Nouragues Natural Reserve, French Guiana. We addressed the question of how Manilkara density and fruits at the community level might be major causes of variability in feeding assemblages between tree species. We thus explored how the frugivore assemblages differed between forest patches with contrasting relative Manilkara density and fruiting context. During the daytime, Alouatta seniculus was more often observed in M. huberi crowns at Petit Plateau (PP) with the greatest density of Manilkara spp. and the lowest fruit diversity and availability, whereas Cebus apella and Saguinus midas were more often observed in M. bidentata crowns at both Grand Plateau (GP), with a lowest density of M. bidentata and overall greater fruit supply, and PP. Overall, nearly 53% and 15% of the M. bidentata seed crop at GP and PP, respectively, and about 47% of the M. huberi seed crop were removed, otherwise either spit out or defecated beneath trees, or dropped in fruits. Small-bodied primates concentrated fallen seeds beneath parent trees while large-bodied primate species removed and dispersed more seeds away from parents. However, among the latter, satiated A. seniculus wasted seeds under conspecific trees at PP. Variations in feeding assemblages, seed removal rates and fates possibly reflected interactions with extra-generic fruit species at the community level, according to feeding choice, habitat preferences and ranging patterns of primate species.

Talar morphology of azibiids, strepsirhine-related primates from the Eocene of Algeria: Phylogenetic affinities and locomotor adaptation

The HGL-50 locality, situated on the Glib Zegdou outlier in the Gour Lazib of Algeria (Hammada du Dra), is famous for having yielded several dental remains of primates dating from the late Early to the early Middle Eocene. These primates include Algeripithecus minutus, Azibius trerki and a new species of cf. Azibius (not described yet). Algeripithecus was widely acknowledged to be one of the oldest known anthropoids from Africa. However, very recent discoveries strongly suggest that Algeripithecus is closely related to Azibius and that both taxa are phylogenetically remote from the clade Anthropoidea. Algeripithecus and Azibius make up the family Azibiidae and appear as stem strepsirhines. Here we describe and analyse two ankle bones (tali) found in HGL-50. UM/HGL50-466 is a small left talus, which is appropriate in size to belong to A. trerki, while UM/HGL50-467 is a right talus, which is significantly larger and appropriate in size to belong to the new large species of cf. Azibius. Both tali exhibit a suite of features that resemble conditions primarily found in extinct and extant strepsirhine and adapiform primates; conditions that are consistent with the strepsirhine-like dentition characterizing azibiids. Functionally, these two tali indicate that Azibius species were engaged in a form of active arboreal quadrupedalism with some ability to climb and leap. Azibiids were rather small-bodied primates, approximating the size of some modern dwarf lemurs (Cheirogaleidae) and sportive lemurs ( Lepilemuridae) from Madagascar. Given their small body-size and their talar morphology, living cheirogaleid lemurs, which are agile arboreal quadrupeds (with climbing, springing and branch running activities), might appear as good analogues for azibiids in terms of locomotor behaviour.

Substrate determines asymmetrical gait dynamics in marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri boliviensis)

Studies of skeletal pathology indicate that injury from falling accounts for most long bone trauma in free-ranging primates, suggesting that primates should be under strong selection to manifest morphological and behavioral mechanisms that increase stability on arboreal substrates. Although previous studies have identified several kinematic and kinetic features of primate symmetrical gaits that serve to increase arboreal stability, very little work has focused on the dynamics of primate asymmetrical gaits. Nevertheless, asymmetrical gaits typify the rapid locomotion of most primates, particularly in smaller bodied taxa. This study investigated asymmetrical gait dynamics in growing marmosets and squirrel monkeys moving on terrestrial and simulated arboreal supports (i.e., an elevated pole). Results showed that monkeys used several kinematic and kinetic adjustments to increase stability on the pole, including reducing peak vertical forces, limiting center of mass movements, increasing substrate contact durations, and using shorter and more frequent strides (thus limiting disruptive whole-body aerial phases). Marmosets generally showed greater adjustment to pole locomotion than did squirrel monkeys, perhaps as a result of their reduced grasping abilities and retreat from the fine-branch niche. Ontogenetic increases in body size had relatively little independent influence on asymmetrical gait dynamics during pole locomotion, despite biomechanical theory suggesting that arboreal instability is exacerbated as body size increases relative to substrate diameter. Overall, this study shows that 1) symmetrical gaits are not the only stable way to travel arboreally and 2) small-bodied primates utilize specific kinematic and kinetic adjustments to increase stability when using asymmetrical gaits on arbo real substrates.

Vocal Response of Captive-reared Saguinus oedipus During Mobbing

Mobbing is an important component of antipredator behavior for animals from many taxa. Callitrichids are small-bodied primates that mob multiple types of predators. Though there have been several observations of callitrichids mobbing predators in the wild, their anecdotal nature provides only rough descriptions of behavior and vocalizations. Researchers could neither spectrographically identify nor quantify vocalizations owing to the limitations of observing predation in the field. We examined in detail the mobbing response of 1 callitrichid species, the cotton-top tamarin, in captivity. We recorded vocalizations for quantitative analysis and observed behavior qualitatively. We report 3 new vocalizations that had not been described in the original repertoire for the cotton-top tamarin. Analysis of the time course of a mobbing session yielded a pattern in which the highest intensity mobbing vocalizations decreased over the session even though lower intensity vocalizing continued, which may reflect a shifting strategy from mobbing to vigilance. The rate of calling during mobbing sessions differed from the rate of calling during control sessions. We discuss the vocalizations in relation to 2 hypotheses of form and function of antipredator calls. The newly described mobbing vocalizations may have an important impact on the study of mobbing because they represent a class of vocalizations that researchers have largely ignored in studies of callitrichids, thus raising new issues concerning past and future research on antipredator behavior in the family.