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ABSTRACT Laboratory studies have broadened our understanding of primate arboreal locomotor biomechanics and adaptation but are necessarily limited in species availability and substrate complexity. In this field study, we filmed the locomotion of 11 species of platyrrhines (Ecuador and Costa Rica;n = 1234 strides) and remotely measured substrate diameter and orientation. We then explored ecological and phylogenetic influences on quadrupedal kinematics in multivariate space using redundancy analysis combined with variation partitioning. Among all species, phylogenetic relatedness more strongly influenced quadrupedal kinematics than variation in substrate. Callitrichines were maximally divergent from other taxa, driven by their preferred use of higher speed asymmetrical gaits. Pitheciids were also distinctive in their use of lower limb phases, including lateral sequence gaits. The biomechanical implications of interspecific differences in body mass and limb proportions account for a substantial portion of the phylogenetic‐based variation. Body mass and kinematic variation were inversely related–whereas the larger taxa (atelids) were relatively restricted in kinematic space, and preferred more stable, symmetrical gaits, the smallest species (callitrichines) used faster, more asymmetrical and less cautious gaits along with symmetrical gaits. Intermembral index had a positive relationship with limb phase, consistent with higher limb phases in atelines compared to pitheciids. Substrate alone accounted for only 2% of kinematic variation among all taxa, with substrate orientation influencing kinematics more than diameter. Substrate effects, though weak, were generally consistent with predictions and with previous laboratory and field‐based research. Excluding callitrichines and asymmetrical gaits, the influence of substrate alone remained low (2%), and the phylogenetic signal dropped from 31% to 8%. The substantial residual kinematic variation may be attributable to substrate or morphological variables not measured here, but could also reflect basic biomechanical patterns shared by all taxa that serve them well when moving arboreally, regardless of the challenges provided by any particular substrate. 

Research on primates’ aptitude for navigating fine, compliant, and oblique branches has often focused on their postcranial morphology and locomotor mechanics. Here we aim to understand how primates perceive risk and make informed judgments to move safely. We video-recorded and digitized the locomotion of four lemur species (Ranomafana National Park) and 3 cercopithecoid monkeys (Kibale National Park). We test the general hypothesis that primates should change their gaits and engage in exploratory behaviors – using touch and sight as guides – to increase stability in precarious settings. Augmenting our prior study showing that some lemurs change their locomotion when moving high in the canopy, we present new data on the behavior of wild lemurs and monkeys as they cross gaps between substrates or switch between locomotor modes. They frequently cross gaps and transition between modes without pause, meaning they can accurately gauge their locomotor capacity before moving onto a new substrate. In an investigation on four species of captive lemurs (Duke Lemur Center), we examine how variations in substrate diameter, orientation, and compliance influence the paths lemurs choose to take. Preliminary results suggest that lemurs will tend to avoid the most precarious substrates in their paths, and future analysis will examine the role that light availability plays as well. Overall, this research highlights the importance of risk perception for robust locomotor performance while moving in arboreal environments. 

Much research on primate locomotor performance in arboreal settings focuses on how primate morphology allows them to navigate substrates that vary in diameter, orientation, and compliance. However, little prior research has considered how these and other environmental factors - such as substrate height and light availability - may also affect locomotor behavior by altering how risky a given substrate is perceived to be. To investigate the relationship between risk perception and locomotor performance, we video-recorded four species of wild lemur (Ranomafana National Park), three species of wild cercopithecoid monkeys (Kibale National Park), and four species of captive lemur (Duke Lemur Center). We test the general hypothesis that primates should change their gaits and engage in exploratory behaviors – using touch and sight as guides – to increase stability in precarious settings. Augmenting our prior study showing that some lemurs change their locomotion when moving high in the canopy, we present new data showing that wild lemurs and monkeys frequently cross gaps between substrates and transition between locomotor modes without pause. In the investigation on captive lemurs, we examine whether variations in branch diameter, compliance, orientation, and light availability influence the paths lemurs choose to take. Preliminary results suggest that lemurs tend to avoid the most precarious substrates (i.e., the most narrow and compliant) regardless of lighting conditions. Overall, this research indicates that primates are able to make quick and accurate judgements about locomotor safety in the context of ongoing arboreal locomotion. 

ABSTRACT Jumping is a crucial behavior in fitness-critical activities including locomotion, resource acquisition, courtship displays and predator avoidance. In primates, paleontological evidence suggests selection for enhanced jumping ability during their early evolution. However, our interpretation of the fossil record remains limited, as no studies have explicitly linked levels of jumping performance with interspecific skeletal variation. We used force platform analyses to generate biomechanical data on maximal jumping performance in three genera of callitrichine monkeys falling along a continuum of jumping propensity: Callimico (relatively high propensity jumper), Saguinus (intermediate jumping propensity) and Callithrix (relatively low propensity jumper). Individuals performed vertical jumps to perches of increasing height within a custom-built tower. We coupled performance data with high-resolution micro-CT data quantifying bony features thought to reflect jumping ability. Levels of maximal performance between species – e.g. maximal take-off velocity of the center of mass (CoM) – parallel established gradients of jumping propensity. Both biomechanical analysis of jumping performance determinants (e.g. CoM displacement, maximal force production and peak mechanical power during push-off) and multivariate analyses of bony hindlimb morphology highlight different mechanical strategies among taxa. For instance, Callimico, which has relatively long hindlimbs, followed a strategy of fully extending of the limbs to maximize CoM displacement – rather than force production – during push-off. In contrast, relatively shorter-limbed Callithrix depended mostly on relatively high push-off forces. Overall, these results suggest that leaping performance is at least partially associated with correlated anatomical and behavioral adaptations, suggesting the possibility of improving inferences about performance in the fossil record. 

Abstract Several studies comparing primate locomotion under lab versus field conditions have shown the importance of implementing both types of studies, as each has their advantages and disadvantages. However, three‐dimensional (3D) motion capture of primates has been challenging under natural conditions. In this study, we provide a detailed protocol on how to collect 3D biomechanical data on primate leaping in their natural habitat that can be widely implemented. To record primate locomotion in the dense forest we use modified GoPro Hero Black cameras with zoom lenses that can easily be carried around and set up on tripods. We outline details on how to obtain camera calibrations at greater heights and how to process the collected data using the MATLAB camera calibration app and the motion tracking software DLTdv8a. We further developed a new MATLAB application “WildLeap3D” to generate biomechanical performance metrics from the derivedx,y,zcoordinates of the leaps. We provide details on how to collect data on support diameter, compliance, and orientation, and combine these with the jumps to study locomotor performance in an ecological context. We successfully reconstructed leaps of wild primates in the 3D space under natural conditions and provided data on four representative leaps. We provide exemplar data on primate velocity and acceleration during a leap and show how our protocol can be used to analyze segmental kinematics. This study will help to make motion capture of freely moving animals more accessible and help further our knowledge about animal locomotion and movement. 

Abstract ObjectivesDespite qualitative observations of wild primates pumping branches before leaping across gaps in the canopy, most studies have suggested that support compliance increases the energetic cost of arboreal leaping, thus limiting leaping performance. In this study, we quantified branch pumping behavior and tree swaying in wild primates to test the hypothesis that these behaviors improve leaping performance. Materials and MethodsWe recorded wild colobine monkeys crossing gaps in the canopy and quantitatively tracked the kinematics of both the monkey and the compliant support during behavioral sequences. We also empirically measured the compliance of a sample of locomotor supports in the monkeys' natural habitat, allowing us to quantify the resonant properties of substrates used during leaping. ResultsAnalyses of three recordings show that adult red colobus monkeys (Piliocolobus tephrosceles) use branch compliance to their advantage by actively pumping branches before leaping, augmenting their vertical velocity at take‐off. Quantitative modeling of branch resonance periods, based on empirical measurements of support compliance, suggests that monkeys specifically employed branch pumping on relatively thin branches with protracted periods of oscillation. Finally, an additional four recordings show that both red colobus and black and white colobus monkeys (Colobus guereza) utilize tree swaying to cross large gaps, augmenting horizontal velocity at take‐off. DiscussionThis deliberate branch manipulation to produce a mechanical effect for stronger propulsion is consistent with the framework of instrumental problem‐solving. To our knowledge, this is the first study of wild primates which quantitatively shows how compliant branches can be used advantageously to augment locomotor performance. 

Abstract ObjectivesAn accident during arboreal locomotion can lead to risky falls, but it remains unclear that the extent to which primates, as adept arborealists, change their locomotion in response to the perceived risk of moving on high supports in the tree canopy. By using more stable forms of locomotion on higher substrates, primates might avoid potentially fatal consequences. Materials and MethodsUsing high‐speed cameras, we recorded the quadrupedal locomotion of four wild lemur species—Eulemur rubriventer,Eulemur rufifrons, Hapalemur aureus, and Lemur catta(N = 113 total strides). We quantified the height, diameter, and angular orientation of locomotor supports using remote sensors and tested the influence of support parameters on gait kinematics, specifically predicting that in response to increasing substrate height, lemurs would decrease speed and stride frequency, but increase stride length and the mean number of supporting limbs. ResultsLemurs did not adjust stride frequency on substrates of varying height. Adjustments to speed, stride length, and the mean number of supporting limbs in response to varying height often ran counter to predictions. OnlyE. rubriventerdecreased speed and increased the mean number of supporting limbs on higher substrates. DiscussionResults suggest that quadrupedal walking is a relatively safe form of locomotion for lemurs, requiring subtle changes in gait to increase stability on higher—that is, potentially riskier—substrates. Continued investigation of the impact of height on locomotion will be important to determine how animals assess risk in their environment and how they choose to use this information to move more safely.