Positional Behavior of Introduced Monk Parakeets (Myiopsitta monachus) in an Urban Landscape

Simple Summary

Positional behaviors comprise the entirety of animals’ locomotion and posture. Often, these positional behaviors are paired with information about sußbstrate characteristics (e.g., orientation, diameter, texture, height) and frequency to gain an ecological perspective of when and why an animal utilizes a particular behavior. Thus far, quantitative studies of positional behavior have been limited to mammals, leaving a major gap in our understanding of how animals utilize their environment. In this study, we present the first quantitative report of positional behavior within Aves, presenting scan sampling data from an established colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Parrots exhibited a strong preference for small and terminal branches when perching arboreally. Such a pattern is consistent with arboreal primates. We also observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the potential importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species and underscores the need for further studies exploring positional behaviors among urban wildlife.

Abstract

Positional behaviors have been broadly quantified across the Order Primates, and in several other mammalian lineages, to contextualize adaptations to, and evolution within, an arboreal environment. Outside of Mammalia, however, such data are yet to be reported. In this study, we present the first quantitative report of positional behavior within Aves, presenting 11,246 observations of scan sampling data from a colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Each scan recorded locomotor and postural behavior and information about weather condition, temperature, and substrate properties (e.g., type, size, orientation). A distinction was also recorded between natural and artificial substrates. Parrots exhibited a strong preference for small and terminal branches, a selection which may reflect targeted foraging of new fruit growth and leaf-buds. We further observed that the gait transition from walking to sidling appears primarily driven by substrate size, with the former preferred on the ground and on large, broad substrates and the latter used to navigate smaller branches. Finally, we observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species.

Testing mechanisms for weight support distribution during inverted quadrupedalism in primates

A key characteristic of primate above-branch arboreal locomotion is hindlimb-biased weight support, subverting the typical mammalian condition in which the majority of the body weight is supported by the forelimb. This shift is thought to reflect an adaptation toward the arboreal niches exploited by early primates. However, above-branch quadrupedalism represents only one locomotor mode employed by primates in arboreal contexts. Inverted quadrupedal gaits, in which primates are suspended beneath branches by their hands and feet, have been documented in more than 50 primate taxa. This gait is characterized by a return to forelimb-biased weight distributions and a transition from peak vertical forces being greatest in the hindlimb to being greatest in the forelimb, which may occur to protect the hindlimb from high magnitudes of tensile loading when inverted. In this study, we compare kinetic and kinematic data during upright and inverted quadrupedalism in Lemur catta, Varecia variegata, Cebus capucinus, and Saimiri sciureus. These data are referenced against a classical inverted quadrupedal model: the two-toed sloth (Choloepus didactylus). Our findings show that inverted quadrupedalism in primates is differentiated from above-branch quadrupedalism by increases in forelimb weight support, forelimb contact times, and both forelimb and hindlimb joint excursions. Previously postulated biomechanical models outlining mechanisms relating to the control of weight support during upright walking do not translate well to inverted quadrupedal walking. We suggest that inverted primates may simply be adopting basal neuromuscular gait characteristics and applying them facultatively to this infrequent locomotor behavior.

Does a suspensory lifestyle result in increased tensile strength?: Organ level material properties of sloth limb bones

The material composition of vertebrate connective tissue is highly conserved across taxa. Existing data suggest that the compressive and tensile strength of limb bones are very similar despite marked variation in limb posture and locomotor patterns. However, the material properties of limb bone tissue from suspensory taxa have not been formally evaluated. Sloths are nearly obligatory in their use of below-branch suspensory locomotion and posture, thus placing their limb bones and associated soft tissue structures under routine tensile loading. It is possible that sloth limb bones are modified for enhanced tensile strength, perhaps at the expense of compressive strength. Fore- and hindlimb bones of two-toed (Choloepus hoffmanni) and three-toed (Bradypus variegatus) sloths were tested in compression and bending to evaluate this hypothesis. Strength and elastic (Young's) modulus were similarly lower in sloth limb bones during both compression and bending, as compared to pronograde taxa. Ratios of peak bending strength to compressive strength additionally were elevated (sloths: 1.4-1.7; upright taxa: 0.6-1.2) for sloth limb bones. Overall, the material properties measured from the limb bones of tree sloths support our hypothesis of predicted function in a tensile limb system. Future studies should aim to directly test bones in tension to confirm indications of elevated axial tensile strength. Nevertheless, the results herein expand understanding of functional adaptation in mammalian tissue for a range of locomotor/postural behaviors that were previously unexplored.

Strepsirrhine Primate Training Programs in North American Institutions: Status and Implications for Future Welfare Assessment

Simple Summary

Training techniques are based on operant conditioning learning (the behavior is modified by its consequences). In many nonhuman primate species, they have been used to influence animals to perform specific behaviors voluntarily and cooperate with routine husbandry and veterinary procedures. However, the information regarding the suborder of strepsirrhine primates (lemurs, lorises, and galagos) is scarce. We assessed the development and current status of training programs with these species in North American institutions through an online survey. We collected information related to training program details; animals, behaviors, and techniques; the evaluation process; and the impact of training. Seventy-one organizations completed the survey, with results showing that 97% trained their strepsirrhines with the main objectives of husbandry and veterinary care (around 80%). Sixty-eight percent of organizations did not report any risk in training these species. The benefits reported include increases in positive human–animal interactions, psychological well-being, and staff awareness of animal behaviors, supporting the success of these programs in providing optimal care for these nonhuman primates. However, we need to improve our understanding of the impact of training on the welfare of strepsirrhine primates, and we hope that the data offered in this survey can help in this future assessment.

Abstract

Many articles have shown the benefits of operant conditioning training techniques in the care and welfare of several species of nonhuman primates; however, the information regarding their use in strepsirrhine species is scarce. We assessed the development and current status of training programs with these species in North American institutions. An online survey was distributed through members of the Association of Zoos and Aquariums using a multiple-choice format. We collected information related to training program details; animals, behaviors, and techniques; the evaluation process; and the impact of training. Seventy-one organizations completed the survey, with the results showing that 97% of respondents trained their strepsirrhines with the main objective of husbandry and veterinary care (around 80%). Sixty-eight percent of organizations did not report any risk in training these species. The benefits reported include increases in positive human–animal interactions (97%), psychological well-being (88%), and staff awareness of animal behaviors (90%). However, a multi-dimensional approach to measure the efficacy of training could provide a deeper understanding of its impact on the welfare of strepsirrhine primates. We hope that the data offered in this survey can help in this future assessment.

A Horse of a Different Color?: Tensile Strength and Elasticity of Sloth Flexor Tendons

Tendons must be able to withstand the tensile forces generated by muscles to provide support while avoiding failure. The properties of tendons in mammal limbs must therefore be appropriate to accommodate a range of locomotor habits and posture. Tendon collagen composition provides resistance to loading that contributes to tissue strength which could, however, be modified to not exclusively confer large strength and stiffness for elastic energy storage/recovery. For example, sloths are nearly obligate suspenders and cannot run, and due to their combined low metabolic rate, body temperature, and rate of digestion, they have an extreme need to conserve energy. It is possible that sloths have a tendon "suspensory apparatus" functionally analogous to that in upright ungulates, thus allowing for largely passive support of their body weight below-branch, while concurrently minimizing muscle contractile energy expenditure. The digital flexor tendons from the fore- and hindlimbs of two-toed (Choloepus hoffmanni) and three-toed (Bradypus variegatus) sloths were loaded in tension until failure to test this hypothesis. Overall, tensile strength and elastic (Young's) modulus of sloth tendons were low, and these material properties were remarkably similar to those of equine suspensory "ligaments." The results also help explain previous findings in sloths showing relatively low levels of muscle activation in the digital flexors during postural suspension and suspensory walking.

Headfirst descent behaviors in a comparative sample of strepsirrhine primates

The ability to safely ascend and descend is critical to the success of arboreal animals. Nonprimate mammals typically descend supports headfirst aided by their claws, but primates must rely on grasping, and use a variety of behaviors to move down within an arboreal environment, including headfirst and tailfirst descending. This study assesses hypothesized body mass limits on vertical headfirst descent and identifies approximate support orientations and diameters at which headfirst descent is ceased in a sample of nine strepsirrhines species ranging in mass from 0.06 to 4.5 kg. Species under 1 kg, arboreal quadrupeds Cheirogaleus medius and Microcebus murinus, and slow climber Nycticebus pygmaeus, always descended supports headfirst regardless of orientation and diameter as long as a grasp could be established. Arboreal quadrupedal species above 1 kg, Daubetonia madagascariensis, Eulemur coronatus, Eulemur mongoz, Lemur catta, and Varecia variegata differed in the orientation at which they ceased using headfirst descent and the types of alternative descending behaviors they employed. Lemur catta, a highly terrestrial species, started to employ tailfirst descents at 45° and completely stopped using headfirst descent on steeper and thicker supports. Other arboreal quadrupeds, D. madagascariensis, E. coronatus, E. mongoz, and V. variegata, began using tailfirst descent at 60°. The vertical clinging and leaping species Propithecus coquereli rarely engaged in above branch quadrupedalism, and individuals were observed using tailfirst descents on supports as shallow as 15°. This study shows the ways in which mass and anatomy may constrain use of headfirst descent through arboreal environments, and the alternate strategies strepsirrhine primates employ to descend.

Correlation between musculoskeletal structure of the hand and primate locomotion: Morphometric and mechanical analysis in prehension using the cross- and triple-ratios

Biometric ratios of the relative length of the rays in the hand have been analyzed between primate species in the light of their hand function or phylogeny. However, how relative lengths among phalanges are mechanically linked to the grasping function of primates with different locomotor behaviors remains unclear. To clarify this, we calculated cross and triple-ratios, which are related to the torque distribution, and the torque generation mode at different joint angles using the lengths of the phalanges and metacarpal bones in 52 primates belonging to 25 species. The torque exerted on the finger joint and traction force of the flexor tendons necessary for a cylindrical grip and a suspensory hand posture were calculated using the moment arm of flexor tendons measured on magnetic resonance images, and were compared among Hylobates spp., Ateles sp., and Papio hamadryas. Finally, the torques calculated from the model were validated by a mechanical study detecting the force exerted on the phalanx by pulling the digital flexor muscles during suspension in these three species. Canonical discriminant analysis of cross and triple-ratios classified primates almost in accordance with their current classification based on locomotor behavior. The traction force was markedly reduced with flexion of the MCP joint parallel to the torque in brachiating primates; this was notably lower in the terrestrial quadrupedal primates than in the arboreal primates at mild flexion. Our mechanical study supported these features in the torque and traction force generation efficiencies. Our results suggest that suspensory or terrestrial quadrupedal primates have hand structures that can exert more torque at a suspensory posture, or palmigrade and digitigrade locomotion, respectively. Furthermore, our study suggests availability of the cross and triple-ratios as one of the indicators to estimate the hand function from the skeletal structure.

A 60:40 split: Differential mass support in dogs

Dogs have been bred for different sizes and functions, which can affect their locomotor biomechanics. As quadrupeds, dogs must distribute their mass between fore and hind legs when standing. The mass distribution in dogs was studied to determine if the proportion of supported mass on each limb couplet is dependent on body size. A total of 552 dogs from 123 breeds ranging in size from Chihuahua to Mastiff were examined. Each dog was weighed on a digital scale while standing, alternating foreleg, and hind leg support. The overall "grand" mean proportion of mass on the forelegs to the total mass was 60.4% (range: 47.6-74.4%). The data set indicated no significant change in the ratio with total mass but there was a significant difference by sex. When separated into American Kennel Club categories, no group was notably different from the grand mean or from each other, but when sex was also considered, there was a significant difference that was not specifically discerned by post hoc analysis. The mean for female Hounds was notably below the grand mean. For clades based on genetics, the mean for European origin mastiffs was notably greater than the grand mean and significantly different from UK origin herders and coursers. The mass of the head, chest, and musculature for propulsion could explain the mass support differential. Mass distribution and terrestrial locomotion in dogs shows substantial variation among breeds.

Variation in limb loading magnitude and timing in tetrapods

Comparative analyses of locomotion in tetrapods reveal two patterns of stride cycle variability. Tachymetabolic tetrapods (birds and mammals) have lower inter-cycle variation in stride duration than bradymetabolic tetrapods (amphibians, lizards, turtles and crocodilians). This pattern has been linked to the fact that birds and mammals share enlarged cerebella, relatively enlarged and heavily myelinated Ia afferents, and γ-motoneurons to their muscle spindles. Both tachymetabolic tetrapod lineages also possess an encapsulated Golgi tendon morphology, thought to provide more spatially precise information on muscle tension. The functional consequence of this derived Golgi tendon morphology has never been tested. We hypothesized that one advantage of precise information on muscle tension would be lower and more predictable limb bone stresses, achieved in tachymetabolic tetrapods by having less variable substrate reaction forces than bradymetabolic tetrapods. To test this hypothesis, we analyzed hindlimb substrate reaction forces during locomotion of 55 tetrapod species in a phylogenetic comparative framework. Variation in species means of limb loading magnitude and timing confirm that, for most of the variables analyzed, variance in hindlimb loading and timing is significantly lower in species with encapsulated versus unencapsulated Golgi tendon organs. These findings suggest that maintaining predictable limb loading provides a selective advantage for birds and mammals by allowing energy savings during locomotion, lower limb bone safety factors and quicker recovery from perturbations. The importance of variation in other biomechanical variables in explaining these patterns, such as posture, effective mechanical advantage and center-of-mass mechanics, remains to be clarified.

Linking Gait Dynamics to Mechanical Cost of Legged Locomotion

For millenia, legged locomotion has been of central importance to humans for hunting, agriculture, transportation, sport, and warfare. Today, the same principal considerations of locomotor performance and economy apply to legged systems designed to serve, assist, or be worn by humans in urban and natural environments. Energy comes at a premium not only for animals, wherein suitably fast and economical gaits are selected through organic evolution, but also for legged robots that must carry sufficient energy in their batteries. Although a robot's energy is spent at many levels, from control systems to actuators, we suggest that the mechanical cost of transport is an integral energy expenditure for any legged system—and measuring this cost permits the most direct comparison between gaits of legged animals and robots. Although legged robots have matched or even improved upon total cost of transport of animals, this is typically achieved by choosing extremely slow speeds or by using regenerative mechanisms. Legged robots have not yet reached the low mechanical cost of transport achieved at speeds used by bipedal and quadrupedal animals. Here we consider approaches used to analyze gaits and discuss a framework, termed mechanical cost analysis, that can be used to evaluate the economy of legged systems. This method uses a point mass perspective to evaluate the entire stride as well as to identify individual events that accrue mechanical cost. The analysis of gait began at the turn of the last century with spatiotemporal analysis facilitated by the advent of cine film. These advances gave rise to the “gait diagram,” which plots duty factors and phase separations between footfalls. This approach was supplanted in the following decades by methods using force platforms to determine forces and motions of the center of mass (CoM)—and analytical models that characterize gait according to fluctuations in potential and kinetic energy. Mechanical cost analysis draws from these approaches and provides a unified framework that interprets the spatiotemporal sequencing of leg contacts within the context of CoM dynamics to determine mechanical cost in every instance of the stride. Diverse gaits can be evaluated and compared in biological and engineered systems using mechanical cost analysis.

Do forelimb shape and peak forces co-vary in strepsirrhines?

OBJECTIVES

In this study, we explore whether ground reaction forces recorded during horizontal walking co-vary with the shape of the long bones of the forelimb in strepsirrhines. To do so, we quantify (1) the shape of the shaft and articular surfaces of each long bone of the forelimb, (2) the peak vertical, mediolateral, and horizontal ground reaction forces applied by the forelimb during arboreal locomotion, and (3) the relationship between the shape of the forelimb and peak forces.

MATERIALS AND METHODS

Geometric morphometric approaches were used to quantify the shape of the bones. Kinetic data were collected during horizontal arboreal walking in eight species of strepsirrhines that show variation in habitual substrate use and morphology of the forelimb. These data were then used to explore the links between locomotor behavior, morphology, and mechanics using co-variation analyses in a phylogenetic framework.

RESULTS

Our results show significant differences between slow quadrupedal climbers (lorises), vertical clinger and leapers (sifaka), and active arboreal quadrupeds (ring-tailed lemur, ruffed lemur) in both ground reaction forces and the shape of the long bones of the forelimb, with the propulsive and medially directed peak forces having the highest impact on the shape of the humerus. Co-variation between long bone shape and ground reaction forces was detected in both the humerus and ulna even when accounting for differences in body mass.

DISCUSSION

These results demonstrate the importance of considering limb-loading beyond just peak vertical force, or substrate reaction force. A re-evaluation of osseous morphology and functional interpretations is necessary in light of these findings.

A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two-toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa)

Over the last decade, we have learned much about the anatomy, evolutionary history, and biomechanics of the extant sloths. However, most of this study has involved studying sloths in controlled conditions, and few studies have explored how these animals are behaving in a naturalistic setting. In this study, we integrate positional activities in naturalistic conditions with kinematic and kinetic observations collected on a simulated runway to best capture the biomechanical behavior of Linnaeus's two-toed sloths. We confirm that the dominant positional behaviors consist of hanging below the support using a combination of forelimbs and hindlimbs, and walking quadrupedally below the branches. The majority of these behaviors occur on horizontal substrates that are approximately 5-10 cm in diameter. The kinematics of suspensory walking observed both in the naturalistic settings and on simulated arboreal runways are dominated by movement of the proximal limb elements, while distal limb elements tend to show little excursion. Joint kinematics are similar between the naturalistic setting and the simulated runway, but movements of the shoulder and hip tend to be exaggerated while moving in simulated conditions. Kinetic patterns of the two-toed sloth can be explained almost entirely by considering them as an inverted linked strut. However, medially directed forces toward the substrate were more frequent than expected in the forelimb, which may help sloths maintain a better "grip" on the substrate. This study serves as a model of how to gain a comprehensive understanding of the functional-adaptive profile of a particular species.

Mechanisms for the functional differentiation of the propulsive and braking roles of the forelimbs and hindlimbs during quadrupedal walking in primates and felines

During quadrupedal walking in most animals, the forelimbs play a net braking role, whereas the hindlimbs are net propulsive. However, the mechanism by which this differentiation occurs remains unclear. Here, we test two models to explain this pattern using primates and felines: (1) the horizontal strut effect (in which limbs are modeled as independent struts), and (2) the linked strut model (in which limbs are modeled as linked struts with a center of mass in between). Video recordings were used to determine point of contact, timing of mid-stance, and limb protraction/retraction duration. Single-limb forces were used to calculate contact time, impulses and the proportion of the stride at which the braking-to-propulsive transition (BP) occurred for each limb. We found no association between the occurrence of the BP and mid-stance, little influence of protraction and retraction duration on the braking-propulsive function of a limb, and a causative relationship between vertical force distribution between limbs and the patterns of horizontal forces. These findings reject the horizontal strut effect, and provide some support for the linked strut model, although predictions were not perfectly matched. We suggest that the position of the center of mass relative to limb contact points is a very important, but not the only, factor driving functional differentiation of the braking and propulsive roles of the limbs in quadrupeds. It was also found that primates have greater differences in horizontal impulse between their limbs compared with felines, a pattern that may reflect a fundamental arboreal adaptation in primates.

Comparison of spatiotemporal gait characteristics between vertical climbing and horizontal walking in primates

During quadrupedal walking, most primates utilize diagonal sequence diagonal couplet gaits, large limb excursions, and hindlimb-biased limb-loading. These gait characteristics are thought to be basal to the Order, but the selective pressure underlying these gait changes remains unknown. Some researchers have examined these characteristics during vertical climbing and propose that primate quadrupedal gait characteristics may have arisen due to the mechanical challenges of moving on vertical supports. Unfortunately, these studies are usually limited in scope and do not account for varying strategies based on body size or phylogeny. Here, we test the hypothesis that the spatiotemporal gait characteristics that are used during horizontal walking in primates are also present during vertical climbing irrespective of body size and phylogeny. We examined footfall patterns, diagonality, speed, and stride length in eight species of primates across a range of body masses. We found that during vertical climbing primates slow down, keep more limbs in contact with the substrate at any one time, and increase the frequency of lateral sequence gaits compared to horizontal walking. Taken together these characteristics are assumed to increase stability during locomotion. Phylogenetic relatedness and body size differences have little influence on locomotor patterns observed across species. These data reject the idea that the suite of spatiotemporal gait features observed in primates during horizontal walking are in some way evolutionarily linked to selective pressures associated with mechanical requirements of vertical climbing. These results also highlight the importance of behavioral flexibility for negotiating the challenges of locomotion in an arboreal environment.

An anatomical and mechanical analysis of the douc monkey (genus Pygathrix), and its role in understanding the evolution of brachiation

OBJECTIVES

Pygathrix is an understudied Asian colobine unusual among the Old World monkeys for its use of arm-swinging. Little data exists on the anatomy and mechanics of brachiation in this genus. Here, we consider this colobine to gain insight into the parallel evolution of suspensory behavior in primates.

MATERIALS AND METHODS

This study compares axial and appendicular morphological variables of Pygathrix with other Asian colobines. Additionally, to assess the functional consequences of Pygathrix limb anatomy, kinematic and kinetic data during arm-swinging are included to compare the douc monkey to other suspensory primates (Ateles and Hylobates).

RESULTS

Compared to more pronograde species, Pygathrix and Nasalis share morphology consistent with suspensory locomotion such as its narrower scapulae and elongated clavicles. More distally, Pygathrix displays a gracile humerus, radius, and ulna, and shorter olecranon process. During suspensory locomotion, Pygathrix, Ateles, and Hylobates all display mechanical convergence in limb loading and movements of the shoulder and elbow, but Pygathrix uses pronated wrist postures that include substantial radial deviation during arm-swinging.

DISCUSSION

The adoption of arm-swinging represents a major shift within at least three anthropoid clades and little data exist about its transition. Across species, few mechanical differences are observed during arm-swinging. Apparently, there are limited functional solutions to the challenges associated with moving bimanually below branches, especially in more proximal forelimb regions. Morphological data support this idea that the Pygathrix distal forelimb differs from apes more than its proximal end. These results can inform other studies of ape evolution, the pronograde to orthograde transition, and the convergent ways in which suspensory locomotion evolved in primates.

Work minimization accounts for footfall phasing in slow quadrupedal gaits

Quadrupeds, like most bipeds, tend to walk with an even left/right footfall timing. However, the phasing between hind and forelimbs shows considerable variation. Here, we account for this variation by modeling and explaining the influence of hind-fore limb phasing on mechanical work requirements. These mechanics account for the different strategies used by: (1) slow animals (a group including crocodile, tortoise, hippopotamus and some babies); (2) normal medium to large mammals; and (3) (with an appropriate minus sign) sloths undertaking suspended locomotion across a range of speeds. While the unusual hind-fore phasing of primates does not match global work minimizing predictions, it does approach an only slightly more costly local minimum. Phases predicted to be particularly costly have not been reported in nature.

The evolution of vertical climbing in primates: evidence from reaction forces

Vertical climbing is an essential behavior for arboreal animals, yet limb mechanics during climbing are poorly understood and rarely compared with those observed during horizontal walking. Primates commonly engage in both arboreal walking and vertical climbing, and this makes them an ideal taxa in which to compare these locomotor forms. Additionally, primates exhibit unusual limb mechanics compared with most other quadrupeds, with weight distribution biased towards the hindlimbs, a pattern that is argued to have evolved in response to the challenges of arboreal walking. Here we test an alternative hypothesis that functional differentiation between the limbs evolved initially as a response to climbing. Eight primate species were recorded locomoting on instrumented vertical and horizontal simulated arboreal runways. Forces along the axis of, and normal to, the support were recorded. During walking, all primates displayed forelimbs that were net braking, and hindlimbs that were net propulsive. In contrast, both limbs served a propulsive role during climbing. In all species, except the lorisids, the hindlimbs produced greater propulsive forces than the forelimbs during climbing. During climbing, the hindlimbs tends to support compressive loads, while the forelimb forces tend to be primarily tensile. This functional disparity appears to be body-size dependent. The tensile loading of the forelimbs versus the compressive loading of the hindlimbs observed during climbing may have important evolutionary implications for primates, and it may be the case that hindlimb-biased weight support exhibited during quadrupedal walking in primates may be derived from their basal condition of climbing thin branches.

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

OBJECTIVES

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.

MATERIALS AND METHODS

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.

RESULTS

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.

DISCUSSION

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.