Ultimately, these methods will help researchers identify more precisely how primate gait kinematics respond to the complexity of arboreal habitats, furthering our understanding of the adaptive context in which primate quadrupedalism evolved.

The grasping capabilities and gait kinematics characteristic of primates are often argued to be adaptations for safely moving on small terminal branches. The goal of this study was to identify whether Eastern gray squirrels (Sciurus carolinensis) -arboreal rodents that frequently move and forage on small branches, lack primate-like grasping and gait patterns, and arguably represent extant analogs of a stem primate ancestor -adjust gait kinematics to narrow and non-horizontal branches. We studied locomotor kinematics of free-ranging and laboratory-housed squirrels moving over various substrates. We used high-speed video to film 1) a population of free-ranging squirrels moving on natural substrates and 2) laboratory-housed squirrels moving on horizontal poles. Substrates were coded as small, medium, or large relative to squirrel trunk diameter, and as inclined, declined, or horizontal. Free-ranging squirrels used more gallops and half-bounds on small and medium sized substrates, and more high-impact bounds, with reduced limb lead durations, on declined substrates. Laboratory squirrels moved at higher speeds than free-ranging squirrels and responded to decreasing diameter by using more gallops and half-bounds, lowering speed, and -controlling for speed -increasing mean duty factor, mean number of supporting limbs, and relative forelimb lead duration. Our inability to detect substantial diameter or orientation-related gait adjustments in the wild may be due to a limited accounting of confounding influences (e.g., substrate compliance).Ultimately, studies assessing stability measures (e.g., center of mass fluctuations, peak vertical force) are required to assess whether primates' enhanced grasping and gait patterns engender performance advantages on narrow or oblique substrates.

Arboreal environments present considerable biomechanical challenges for animals moving and foraging among substrates varying in diameter, orientation and compliance. Most studies of quadrupedal gait kinematics in primates and other arboreal mammals have focused on symmetrical walking gaits and the significance of diagonal sequence gaits. Considerably less research has examined asymmetrical gaits, despite their prevalence in small-bodied arboreal taxa. Here, we examined whether and how free-ranging callitrichine primates adjust asymmetrical gait kinematics to changes in substrate diameter and orientation, as well as how variation in gait kinematics affects substrate displacement. We used high-speed video to film free-ranging Saguinus tripartitus and Cebuella pygmaea inhabiting the Tiputini Biodiversity Station, Ecuador. We found that S. tripartitus used bounding and half-bounding gaits on larger substrates versus gallops and symmetrical gaits on smaller substrates, and also shifted several kinematic parameters consistent with attenuating forces transferred from the animal to the substrate. Similarly, C. pygmaea shifted from high-impact bounding gaits on larger substrates to using more half-bounding gaits on smaller substrates; however, kinematic adjustments to substrate diameter were not as profound as in S. tripartitus. Both species adjusted gait kinematics to changes in substrate orientation; however, gait kinematics did not significantly affect empirical measures of substrate displacement in either species. Because of their small body size, claw-like nails and reduced grasping capabilities, callitrichines arguably represent extant biomechanical analogs for an early stage in primate evolution. As such, greater attention should be placed on understanding asymmetrical gait dynamics for insight into hypotheses concerning early primate locomotor evolution.

Our findings highlight the degree to which toughness values can vary among leaves and how this variation can dramatically influence ingestion rates and chewing efficiency in black and white colobus monkeys. Studies that link food mechanical properties with oral processing behaviors will ultimately provide important context for understanding craniofacial and dentognathic traits in primates.

Most investigations of primate scapular morphology use differences in locomotion to explain variation; less is known about how scapular geometry covaries with nonlocomotor behavior. We examined forelimb use during foraging in 4 cercopithecids ranging throughout the Ivory Coast's Tai Forest. During 5-min feeding bouts, we recorded the frequency individuals of Piliocolobus badius, Colobus polykomos, Cercocebus atys and Cercopithecus diana performed 5 forelimb behaviors involved in the acquisition and introduction of food to the oral cavity. Scapulae from these populations were examined to determine whether differences in forelimb use were reflected in features known to correspond with varying degrees of arm flexion, abduction and elevation. Our results reveal that the species differ markedly in forelimb use and that these differences are interpretable via their scapular morphology. For example, P. badius engages in more frequent flexion, abduction and elevation of the arm above the head relative to C. polykomos, and red colobus scapulae are longer craniocaudally and have larger, more cranially directed supraspinous fossae than those of closely related black-and-white colobus. Our attempt to explore how nonlocomotor behavior covaries with skeletal morphology should provide for more informed interpretations of the primate fossil record.

Understanding intraspecific behavioral and dietary variation is critical for assessing primate populations' abilities to persist in habitats characterized by increasing anthropogenic disturbances. While it is evident that some species exhibit considerable dietary flexibility (in terms of species-specific plant parts) in relation to habitat disturbance, it is unclear if primates are characterized by similar variation and flexibility regarding nutrient intake. This study examined the effects of group, season, and reproductive state on nutrient intake and balancing in adult female Colobus angolensis palliatus in the Diani Forest, Kenya. During July 2014 to December 2015, estimates of nutrient intake were recorded for eight females from three groups inhabiting structurally and ecologically distinct forest areas differing in tree species composition and density. There were differences in metabolizable energy (ME) and macronutrient intakes among groups, seasons, and reproductive states. Most notably, females inhabiting one of the more disturbed forest areas consumed less ME and macronutrients compared to females in the more intact forest area. Contrary to prediction, females in early lactation consumed significantly less ME and macronutrients compared to non-lactating and late lactation females. Despite differences in macronutrient intake, the relative contribution of macronutrients to ME were generally more conservative among groups, seasons, and reproductive states. Average daily intake ratios of non-protein energy to available protein ranged from approximately 3.5:1-4.3:1 among groups. These results indicate that female C. a. palliatus demonstrate a consistent nutrient balancing strategy despite significant intergroup differences in consumption of species-specific plant parts. Data from additional colobine species inhabiting different forest types are required to assess the extent to which nutrient balancing is constrained by phylogeny or is more flexible to local ecological conditions.

No abstract

In this project I studied black and white colobus monkeys (Colobus angolensis palliatus) inhabiting the Diani Forest of south coastal Kenya to test whether activity budgets, positional behavior, and support use differed among individuals in three age categories (juveniles, subadults, and adults). Data for three habituated groups were collected from June to August 2012 and from May to July 2014. Instantaneous sampling and pooled data were used to create overall behavior profiles for the three age categories. Activity budgets differed significantly among the categories. Adults rested more and moved less, subadults socialized more, and juveniles moved more often than individuals in the other two age categories. Support use differed, with juveniles and subadults accessing smaller supports more frequently (i.e., juveniles: bough 19.4 %, branch 57.9 %, twig 13.5 %; subadult: bough 18.6 %, branch 64.5 %, twig 8.2 %) whereas adults preferred larger supports (i.e., adults: bough 32.1 %, branch 54.0 %, twig 5.3 %). Despite different support use, locomotor profiles were remarkably consistent among age categories (i.e., ranges: quadrupedal walk 35.0-45.2 %, bound 17.5-25.3 %, climb 11.2-22.7 %, leap 15.1-19.9 %). Sitting was the predominant posture, accounting for 89.5-92.5 % of the posture observed for all age categories. Overall positional profiles of adults and subadults were statistically indistinguishable whereas juveniles differed significantly from adults but not from subadults. It is hypothesized that the different frequency of specific locomotor behaviors, for example bounding, is attributable to morphological changes associated with ontogeny. Nonetheless, these findings support the notion that primates achieve adult-like positional behavior competence during the juvenile life stage.