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1. Program of the 88th Annual Meeting of the American Association of Physical Anthropologists

   https://doi.org/10.1002/ajpa.23802  

   Dunham, Noah T.; McNamara, Allison; Demes, Brigitte; Johnson, Laura A.; Shapiro, Liza J.; Young, Jesse W. (February 2019, American Journal of Physical Anthropology)

   Laboratory investigations have provided important insight into the functional underpinnings of primate locomotor performance; however, it is unclear to what extent gait patterns in the laboratory reflect those of primates moving in natural settings. We filmed quadrupedal loco-motor activity in eight platyrrhine species at the Tiputini Biodiversity Station, Ecuador, and three additional platyrrhine species at La Suerte Biological Field Station, Costa Rica, and also quantified the diameter and orientation of locomotor substrates using remote sensors (N = 1,233 strides). We compared overall arboreal quadrupedal gait kinematic patterns in free-ranging individuals to those of laboratory platyrrhine congenerics. As expected, gait kinematics of free-ranging individuals were more variable than laboratory counterparts. Within the free-ranging dataset, Ateles and Alouatta increased limb phase on inclines (p=0.04; p=0.002, respectively), Lagothrix increased duty factors on inclines (p=0.002), Cebus increased duty factors on declines (p=0.02), and both Saimiri and Saguinus displayed an inverse relationship between limb phase and substrate diameter (p=0.05; p=0.03, respectively). This study confirms the preference for diagonal sequence gaits in free-ranging primates (i.e., 87.9% of all recorded symmetrical strides) and that in both settings primates tend to adjust gait patterns to promote security through longer contact times on non-horizontal substrates and increased limb phase on inclined substrates. We show that laboratory and field investigations of primate locomotion yield consistent patterns but that field studies can capture additional aspects of gait variability and flexibility in response to the increased substrate complexity of natural environments. 

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2. Assessing the Determinants of Platyrrhine Quadrupedal Gait Kinematics in an Ecological and Phylogenetic Framework

   https://doi.org/10.1002/ajp.70009  

   Shapiro, Liza J; Dunham, Noah T; McNamara, Allison; Young, Jesse W; Hieronymus, Tobin L (February 2025, American Journal of Primatology)

   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. 

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3. Ecological and phylogenetic influences on limb joint kinematics in wild primates

   https://doi.org/10.1093/zoolinnean/zlae004  

   Janisch, Judith; McNamara, Allison; Myers, Lydia C; Schapker, Nicole; Dunham, Noah T; Phelps, Taylor; Mundry, Roger; Hieronymus, Tobin; Shapiro, Liza J; Young, Jesse W (February 2024, Zoological Journal of the Linnean Society)

   Abstract Arboreal locomotion is precarious and places multiple challenges upon stability. Studies have shown that captive primates respond to narrower and steeper supports by flexing limb joints and adopting a compliant gait. We tested whether these same kinematic responses are adopted by wild primates freely ranging over a variety of supports in their natural habitats. We recorded five species of platyrrhines, five species of catarrhines, and four species of strepsirrhines with modified GoPro cameras and used remote measurement to quantify substrate characteristics. Video images were imported into ImageJ to measure the angular kinematics of limb joints during quadrupedal locomotion on a variety of arboreal supports. We statistically tested for associations between joint posture and substrate characteristics, and then disentangled the influence of phylogeny and substrate on limb joint kinematics using variation partitioning and redundancy analysis. Our results partially confirm previous kinematic studies and suggest variation in support orientation, more than diameter or compliance, influences quadrupedal gait kinematics. Phylogenetic relatedness explained more variation in the data than substrate properties. This suggests primates either prospectively choose relatively ‘safe’ substrates for locomotion, or that they possess locomotor adaptations independent of limb joint kinematics per se to overcome the challenges of the precarious arboreal environment. 

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4. Investigating the perception of risks during arboreal locomotion in wild and captive primates

   Schapker, Nicole M; Myers, Lydia C; Janisch, Judith; Matar, Ahmad; Pham, Julie; Miller, Aidan; Boghdady, Abdelrahman; Shapiro, Liza J; Young, Jesse W (March 2025, American Journal of Biological Anthropology)

   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. 

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5. Risk perception and locomotor performance in wild and captive primates

   Schapker, Nicole M; Myers, Lydia C; Janisch, Judith; Matar, Ahmad; Pham, Julie; Boghdady, Abdelrahman; Shapiro, Liza J; Young, Jesse W (March 2025, Society of Integrative and Comparative Biology)

   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. 

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