Patterns of positional behavior in mixed-species troops of Callimico goeldii, Saguinus labiatus, and Saguinus fuscicollis in northwestern Brazil

Linking morphology, performance, and habitat utilization: adaptation across biologically relevant 'levels' in tamarins

BACKGROUND

Biological adaptation manifests itself at the interface of different biologically relevant 'levels', such as ecology, performance, and morphology. Integrated studies at this interface are scarce due to practical difficulties in study design. We present a multilevel analysis, in which we combine evidence from habitat utilization, leaping performance and limb bone morphology of four species of tamarins to elucidate correlations between these 'levels'.

RESULTS

We conducted studies of leaping behavior in the field and in a naturalistic park and found significant differences in support use and leaping performance. Leontocebus nigrifrons leaps primarily on vertical, inflexible supports, with vertical body postures, and covers greater leaping distances on average. In contrast, Saguinus midas and S. imperator use vertical and horizontal supports for leaping with a relatively similar frequency. S. mystax is similar to S. midas and S. imperator in the use of supports, but covers greater leaping distances on average, which are nevertheless shorter than those of L. nigrifrons. We assumed these differences to be reflected in the locomotor morphology, too, and compared various morphological features of the long bones of the limbs. According to our performance and habitat utilization data, we expected the long bone morphology of L. nigrifrons to reflect the largest potential for joint torque generation and stress resistance, because we assume longer leaps on vertical supports to exert larger forces on the bones. For S. mystax, based on our performance data, we expected the potential for torque generation to be intermediate between L. nigrifrons and the other two Saguinus species. Surprisingly, we found S. midas and S. imperator having relatively more robust morphological structures as well as relatively larger muscle in-levers, and thus appearing better adapted to the stresses involved in leaping than the other two.

CONCLUSION

This study demonstrates the complex ways in which behavioral and morphological 'levels' map onto each other, cautioning against oversimplification of ecological profiles when using large interspecific eco-morphological studies to make adaptive evolutionary inferences.

A novel method for automatically analysing the activity of fast-moving animals: a case study of Callimico goeldii monkeys housed in a zoological garden

Behavioural indices are recognised as important criteria for assessing animal welfare. One of the basic animal behaviours included in ethograms is their activity. The assessment of fast-moving animals, performed by humans using the visual observation method, is difficult and not very objective. Therefore, the aim of the research was to develop a method of automated analysis of animal activity, particularly useful in the observation of quick and lively individuals, and to prove its suitability for assessing the behaviour of fast-moving animals. A method of automatically assessing animal activity was developed using digital image analysis, with the Python programming language and the OpenCV library being the foundational tools. The research model was Callimico goeldii monkeys housed in a zoological garden. This method has been proved to correlate well (Rs = 0.76) with the visual method of animal behaviour analysis. The developed automatic evaluation of animal behaviour is many times faster than visual analysis, and it enables precise assessment of the daily activity of fast-moving groups of animals. The use of this system makes it possible to obtain an activity index with sub-second resolution, which allows it to be used in online mode as a detector of abnormal animal activity, e.g. early detection of illnesses or sudden events that are manifested by increased or decreased activity in relation to the standard activity pattern.

Behaviour, Furnishing and Vertical Space Use of Captive Callimico (Callimico goeldii): Implications for Welfare

Provision of optimal captive care should be supported by species-specific evidence. Callimico (Callimico goeldii) is a small South American callitrichid primate. This study sought to address gaps in species-specific knowledge and captive management research by examining differences in callimico behaviour across multiple collections, investigating vertical enclosure use and a possible association between specific behaviours and vertical zones. Observational research was conducted at five European Association of Zoos and Aquaria (EAZA) organisations, in exhibits that were visually divided into four vertical zones. Instantaneous scan sampling was used to record behaviour and location of callimico over a six-day period at each collection, exceeding 160 observational hours. Significant differences were observed in foraging between collections and were much lower than the recommendations in Best Practice Guidelines, although near-wild levels were recorded in one enclosure. At an average height of 2 m, callimico utilized a similar vertical space across very different enclosures, regardless of overall available height, reflective of their natural ecology. The association between whole food items and increased foraging time, horizontal branches and locomotion and deep substrate and diversity of behaviours, offers further species-specific evidence of how the callimico use their captive environment. Our findings complement current EAZA guidelines to support species appropriate care for callimico and makes specific recommendations for further research.

Leaping and differential habitat use in sympatric tamarins in Amazonian Peru

Differential habitat use in sympatric species can provide insight into how behavior relates to morphological differences and as a general model for the study of biological adaptations to different functional demands. In Amazonia, closely related sympatric tamarins of the genera Saguinus and Leontocebus regularly form stable mixed-species groups, but exhibit differences in foraging height and locomotor activity. To test the hypothesis that two closely related species in a mixed-species group prefer different modes of leaping regardless of the substrates available, we quantified leaping behavior in a mixed-species group of Saguinus mystax and Leontocebus nigrifrons. We studied leaping behavior in relation to support substrate type and foraging height in the field for 5 months in the Amazonian forest of north-eastern Peru. Saguinus mystax spent significantly more time above 15 m (79%) and used predominantly horizontal and narrow supports for leaping. Leontocebus nigrifrons was predominantly active below 10 m (87%) and exhibited relatively more trunk-to-trunk leaping. Both species preferred their predominant leaping modes regardless of support type availability in the different forest layers. This indicates that the supports most commonly available in each forest layer do not determine the tamarins’ leaping behavior. This apparent behavioral adaptation provides a baseline for further investigation into how behavioral differences are reflected in the morphology and species-specific biomechanics of leaping behavior and establishes callitrichid primates as a model well-suited to the general study of biological adaptation.

Myological variation in the forearm anatomy of Callitrichidae and Lemuridae

The anatomy of the primate forearm is frequently investigated in terms of locomotor mode, substrate use, and manual dexterity. Such studies typically rely upon broad, interspecific samples for which one or two representative taxa are used to characterize the anatomy of their genus or family. To interpret variation between distantly related taxa, however, it is necessary to contextualize these differences by quantifying variation at lower hierarchical levels, that is, more fine-grained representation within specific genera or families. In this study, we present a focused evaluation of the variation in muscle organization, integration, and architecture within two speciose primate families: the Callitrichidae and Lemuridae. We demonstrate that, within each lineage, several muscle functional groups exhibit substantial variation in muscle organization. Most notably, the digital extensors appear highly variable (particularly among callitrichids), with many unique configurations represented. In terms of architectural variables, both families are more conservative, with the exception of the genus Callimico-for which an increase is observed in forearm muscle mass and strength. We suggest this reflects the increased use of vertical climbing and trunk-to-trunk leaping within this genus relative to the more typically fine-branch substrate use of the other callitrichids. Overall, these data emphasize the underappreciated variation in forearm myology and suggest that overly generalized typification of a taxon's anatomy may conceal significant intraspecific and intrageneric variation therein. Thus, considerations of adaptation within the forearm musculature should endeavor to consider the full range of anatomical variation when making comparisons between multiple taxa within an evolutionary context.

Vertical clinging and leaping induced evolutionary rate shifts in postcranial evolution of tamarins and marmosets (Primates, Callitrichidae)

BACKGROUND

Callitrichids comprise a diverse group of platyrrhine monkeys that are present across South and Central America. Their secondarily evolved small size and pointed claws allow them to cling to vertical trunks of a large diameter. Within callitrichids, lineages with a high affinity for vertical supports often engage in trunk-to-trunk leaping. This vertical clinging and leaping (VCL) differs from horizontal leaping (HL) in terms of the functional demands imposed on the musculoskeletal system, all the more so as HL often occurs on small compliant terminal branches. We used quantified shape descriptors (3D geometric morphometrics) and phylogenetically-informed analyses to investigate the evolution of the shape and size of the humerus and femur, and how this variation reflects locomotor behavior within Callitrichidae.

RESULTS

The humerus of VCL-associated species has a narrower trochlea compared with HL species. It is hypothesized that this contributes to greater elbow mobility. The wider trochlea in HL species appears to correspondingly provide greater stability to the elbow joint. The femur in VCL species has a smaller head and laterally-oriented distal condyles, possibly to reduce stresses during clinging. Similarly, the expanded lesser trochanters visible in VCL species provide a greater lever for the leg retractors and are thus also interpreted as an adaptation to clinging. Evolutionary rate shifts to faster shape and size changes of humerus and femur occurred in the Leontocebus clade when a shift to slower rates occurred in the Saguinus clade.

CONCLUSIONS

Based on the study of evolutionary rate shifts, the transition to VCL behavior within callitrichids (specifically the Leontocebus clade) appears to have been an opportunity for radiation, rather than a specialization that imposed constraints on morphological diversity. The study of the evolution of callitrichids suffers from a lack of comparative analyses of limb mechanics during trunk-to-trunk leaping, and future work in this direction would be of great interest.

Asymmetrical gait kinematics of free-ranging callitrichines in response to changes in substrate diameter and orientation

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 examine 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 Saguinus 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, Cebuella 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 Saguinus. 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. Due to their small body size, claw-like nails, and reduced grasping capabilities, callitrichines arguably represent extant biomechanical analogues 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.

Primate Positional Behavior Development and Evolution

Positional behavior (posture and locomotion) studies are a category of primatological and anthropological field research that attempts to describe movement capabilities and expressed behavior within an evolutionary, ecological, and/or morphological context. This area of research is appealing because it allows the integration of morphological data (capabilities) with expressed behaviors and provides a basis for understanding fossil reconstruction. Because positional behavior acts as a mediator between the biology and the environment, it offers information about virtually all aspects of a primate's life. We are currently undergoing an increase in the number of field projects focusing on the development of positional behaviors in immature primates, and results suggest that in many species positional competence develops relatively early. In this review, I present information on recent positional behavior studies with a focus on how positional behavior develops in young primates. Research on immature primates suggests that natural selection operates at all life stages to influence survival and that the adult positional repertoire likely reflects the challenges confronted by younger individuals.

Age- and sex-based patterns of positional behavior and substrate utilization in the golden snub-nosed monkey (Rhinopithecus roxellana)

Body mass plays an important role in primate positional behavior and in sexually dimorphic arboreal primate species may influence how immature and adult individuals travel through the forest canopy and access food resources. In this study, we examined age- and sex-based patterns of positional behavior and substrate utilization in wild golden snub-nosed monkeys (Rhinopithecus roxellana), an endangered species of Asian colobine. Our results indicated that among all age and sex classes, sitting was the most common feeding and resting posture and during travel, quadrupedal walking was the dominant locomotor behavior. Despite the fact that adult male R. roxellana are reported to exhibit a body mass nearly two times that of adult females, we found no significant sex differences in the positional repertoire during feeding and traveling. In addition, we found that while infants and juveniles used similar postural and locomotor behaviors as their adult counterparts, younger golden snub-nosed monkeys more frequently engaged in risky or escape-oriented behaviors such as climbing, running, leaping, and forelimb suspension. With increasing age, the use of quadrupedal walking and dropping (downward in-air displacement of body mass that does not require hindlimb propulsion) increased and the use of leaping, suspensory postures, and bridging decreased. Finally, given differences in the positional repertoire of adult and immature golden snub-nosed monkeys, we argue that studies of ontogenetic patterns of positional behavior should emphasize what it takes to survive at each life stage rather than what it takes to match an adult repertoire.

Forest type affects prey foraging of saddleback tamarins, Saguinus nigrifrons

Callitrichids can persist in secondary forests where they may benefit from elevated prey abundance. However, how tamarins forage for prey in secondary forest compared to primary forest has not been examined. Using scan and focal sampling, we compared prey foraging and capture success of two groups of Saguinus nigrifrons in north-eastern Peru: one ranging in primary forest, the other with access to a 10-year-old anthropogenic secondary forest. There was a trend for more prey search in the secondary forest, but prey feeding, capture success and size were lower compared to the primary forest. Tamarins avoided the forest floor, used vertical supports less often and searched on a lower variety of substrates in the secondary forest. In the secondary forest, tamarins did not capture flushed prey, which make up a substantial part of the total prey captures biomass in primary forests. Reduced prey capture success is unlikely to reflect reduced prey availability, since more Orthoptera were found in secondary forest through ultrasonic surveys. Therefore, the prey search activity of S. nigrifrons in young secondary forests seemed rather opportunistic, presumably influenced by altered predation patterns, vegetation structure, as well as prey diversity.

Locomotor diversification in new world monkeys: running, climbing, or clawing along evolutionary branches

Modern platyrrhines exhibit a remarkable diversity of locomotor and postural adaptations, which evolved along multiple trajectories since the initial immigration to the island continent of South America. We trace this diversification by reviewing the available paleontological and neontological data for postcranial morphology and ecological adaptation. Fossil platyrrhines are notably diverse, from the Oligocene Branisella, to the varied Patagonian early Miocene quadurpedal-leaping and quadrupedal-climbing fossils of disputed affinities, on through the rich middle Miocene Colombian quadurpedal-leaping forms. More recent taxa exhibit even more derived positional patterns, from the largest suspensory atelids in Pleistocene Brazil, to the remarkable Antillean radiation with suspensory forms and also semiterrestrial species, with postcranial morphology convergent on some Old World monkeys. Field studies of positional behavior of modern platyrrhines set the framework for a spectrum of locomotor adaptations. Central within this spectrum is a cluster of medium-sized species with generalized locomotion (quadrupedal-leaping). At opposite poles lie the more derived conditions: large-bodied species exhibiting locomotor specializations for climbing-suspension; small-bodied species exhibiting adaptations for claw climbing and leaping. This behavior-based spectrum of locomotor diversification is similarly evident in a morphology-based pattern, that is, that produced by the shape of the talus. The implications of the record of platyrrhine postcranial evolution for the competing hypotheses of platyrrhine phylogenetic patterns, the "long lineage hypothesis" and the "stem platyrrhine hypothesis," are considered.

The positional behavior of pygmy marmosets (Cebuella pygmaea) in northwestern Bolivia

Pygmy marmosets are distinctive given their diminutive body size, their year-round reliance upon exudates, and their use of morphologically adapted tegulae to engage in a high degree of claw-clinging behaviors associated with exudate exploitation. This project examined the positional behavior and habitat preferences of one group of pygmy marmosets in a secondary forest within the Department of Pando, northwestern Bolivia. Results from this study indicate that pygmy marmosets primarily use claw-clinging during feeding (89.6%) with preferential use of large vertical trunks. Claw-clinging was also the dominant postural mode during exudate foraging (43.1%) with preferential use of large vertical trunks. Quadrupedalism was the dominant locomotor mode during travel (55.7%) with preferential use of bamboo and medium-sized substrates. These results support previous notions that claw-climbing is a solution to overcome the constraints of small body size while suggesting that quadrupedalism is a habitat-dependent locomotor mode.

An assessment of gum-based environmental enrichment for captive gummivorous primates

In the wild, many primates consume gums exuded from trees, and many species are gum specialists. In spite of this, few data exist concerning gum feeding in captivity. Using a web-based survey of 46 zoos in 12 countries, we evaluated the extent to which zoos feed gum to primates. We found that although callitrichids and galagos receive gum-based enrichment, cercopithecines generally do not. Environmental enrichment is important for stimulating naturalistic behavior to promote the psychological wellbeing of animals. Thus, gum-based enrichment is important for captive gummivores. Our study highlights the need to improve environmental enrichment for captive gummivores, in particular that of cercopithecines. This is most striking for the patas monkey (Erythrocebus patas), an obligate gummivore. The exchange of ecological data between field research and captive settings is crucial, and is just one way primate caretakers can contribute to the conservation and welfare of some of our closest living relatives.

Effects of support size and orientation on symmetric gaits in free-ranging tamarins of Amazonian Peru: implications for the functional significance of primate gait sequence patterns

The adoption of a specific gait sequence pattern during symmetrical locomotion has been proposed to have been a key advantage for the exploitation of the fine branch niche in early primates. Diverse aspects of primate locomotion have been extensively studied in technically equipped laboratory settings, but evolutionary conclusions derived from these investigations have rarely been verified in wild primates. Bridging the gap from the lab to the field, we conducted an actual performance determination of symmetrical gaits in two free-ranging tamarin species (Saguinus mystax and Saguinus fuscicollis) of Amazonian Peru by analyzing high-speed video recordings of naturally occurring locomotor bouts. Tamarins arguably represent viable models for aspects of early primate locomotion. We tested three specific hypotheses derived from laboratory studies to test for the influence of support size and orientation and to gain further insight into the functional significance of primate gait sequence patterns: (1) The tamarins utilize symmetrical gaits at a higher rate on small supports than on larger ones. (2) During symmetrical locomotion on small supports, diagonal sequences are utilized at a higher rate than on larger supports. (3) On inclines, diagonal sequences are predominantly used and on declines, lateral sequences are predominantly used. Our results corroborated hypotheses 1 and 3. We found no clear support for hypothesis 2. In conclusion, our results add to the notion that primate gait plasticity, rather than uniform adoption of diagonal sequence gaits, enabled early primates to accommodate different support types and effectively exploit the small branch niche.

Gait parameter adjustments of cotton-top tamarins (Saguinus oedipus, Callitrichidae) to locomotion on inclined arboreal substrates

The influence of different substrate inclinations on gaits and metric gait parameters (relative forelimb and hind limb protraction, relative forelimb, and hind limb retraction, stride length, stance, and swing phase duration) of cotton-top tamarin locomotion was studied using high-speed video films and evaluated by descriptive and analytical statistical methods. As previously shown, lateral sequence gaits predominantly occurred on descending arboreal substrates (branchlike pole with a smaller diameter than the animal's body). Gait sequence patterns display significant dependency on substrate inclination. Cotton-top tamarins utilize lower diagonality values the more the substrate declines. This tendency leads to a greater use of lateral sequence gaits on steeply declined substrates. Conversely, these primates display the tendency to utilize higher diagonality values the more the substrate inclines leading to the predominant occurrence of diagonal sequence (DS) gaits. Duty factor index, extent of relative protraction, and relative retraction of both limb pairs as well as the relation of forelimb stance phase duration to hind limb stance phase duration is also correlated to the inclination of the substrate. Stride length and swing phase duration display no significant dependence on inclination, but are determined by the speed of the moving animal. The relevant duty factor is approximately constant at all inclinations. Integrating our results with results of other authors we propose a hypothesis for the functional relevance of a utilization of lateral sequence gaits in downward locomotion and DS gaits in upward locomotion. Our data support the notion of a wide ranging behavioral plasticity as a general primate locomotor characteristic.

Forest use and activity patterns of Callimico goeldii in comparison to two sympatric tamarins, Saguinus fuscicollis and Saguinus labiatus

Callimico goeldii, Saguinus fuscicollis, and S. labiatus are sympatric in northern Bolivia and differ from each other in patterns of spatial and structural use of their environment. C. goeldii has a home range five times larger than that of mixed-species troops of S. fuscicollis and S. labiatus. The larger overlapping home range of C. goeldii allows it to move among Saguinus troops, giving it access to a wide range of different microhabitats. All three species use the most common microhabitat in the area, primary forest with dense understory, more than any other microhabitat type. C. goeldii habitat use varies by season, with bamboo and Heliconia microhabitats used more during the dry season. Each species shows preferences for different height classes: C. goeldii is found almost exclusively in the understory, S. fuscicollis uses the understory and middle canopy, and S. labiatus is found mostly in the middle canopy. These height class preferences are reflected in each species' locomotor styles, with C. goeldii showing the highest rates of vertical clinging and leaping, and S. labiatus showing the highest rates of branch-to-branch leaping and quadrupedal movement. The results suggest that C. goeldii may be restricted to forests with dense understory and a mosaic of other microhabitats. Furthermore, C. goeldii does not appear to use its tegulae for large branch foraging, but rather for vertical clinging and leaping between small vertical supports.

Evolutionary implications of the unusual walking mechanics of the common marmoset (C. jacchus)

Several features that appear to differentiate the walking gaits of most primates from those of most other mammals (the prevalence of diagonal-sequence footfalls, high degrees of humeral protraction, and low forelimb vs. hindlimb peak vertical forces) are believed to have evolved in response to requirements of locomotion on thin arboreal supports by early primates that had developed clawless grasping hands and feet. This putative relationship between anatomy, behavior, and ecology is tested here by examining gait mechanics in the common marmoset (Callithrix jacchus), a primate that has sharp claws and reduced pedal grasping, and that spends much of its time clinging on large trunks. Kinematic and kinetic data were collected on three male Callithrix jacchus as they walked across a force platform attached to the ground or to raised horizontal poles. The vast majority of all walking gaits were lateral-sequence. For all steps, the humerus was retracted (<90 degrees relative to a horizontal axis) or held in a neutral (90 degrees ) position at forelimb touchdown. Peak vertical forces on the forelimb were always higher than those on the hindlimb. These three features of the walking gaits of C. jacchus separate it from any other primate studied (including other callitrichids). The walking gaits of C. jacchus are mechanically more similar to those of small, nonprimate mammals. The results of this study support previous models that suggest that the unusual suite of features that typify the walking gaits of most primates are adaptations to the requirements of locomotion on thin arboreal supports. These data, along with data from other primates and marsupials, suggest that primate postcranial and locomotor characteristics are part of a basal adaptation for walking on thin branches.