Vertical clingers and gougers: Rapid acquisition of adult limb proportions facilitates feeding behaviours in young Javan slow lorises ( Nycticebus javanicus )

Slowly Making Sense: A Review of the Two-Step Venom System within Slow (Nycticebus spp.) and Pygmy Lorises (Xanthonycticebus spp.)

Since the early 2000s, studies of the evolution of venom within animals have rapidly expanded, offering new revelations on the origins and development of venom within various species. The venomous mammals represent excellent opportunities to study venom evolution due to the varying functional usages, the unusual distribution of venom across unrelated mammals and the diverse variety of delivery systems. A group of mammals that excellently represents a combination of these traits are the slow (Nycticebus spp.) and pygmy lorises (Xanthonycticebus spp.) of south-east Asia, which possess the only confirmed two-step venom system. These taxa also present one of the most intriguing mixes of toxic symptoms (cytotoxicity and immunotoxicity) and functional usages (intraspecific competition and ectoparasitic defence) seen in extant animals. We still lack many pieces of the puzzle in understanding how this venom system works, why it evolved what is involved in the venom system and what triggers the toxic components to work. Here, we review available data building upon a decade of research on this topic, focusing especially on why and how this venom system may have evolved. We discuss that research now suggests that venom in slow lorises has a sophisticated set of multiple uses in both intraspecific competition and the potential to disrupt the immune system of targets; we suggest that an exudate diet reveals several toxic plants consumed by slow and pygmy lorises that could be sequestered into their venom and which may help heal venomous bite wounds; we provide the most up-to-date visual model of the brachial gland exudate secretion protein (BGEsp); and we discuss research on a complement component 1r (C1R) protein in saliva that may solve the mystery of what activates the toxicity of slow and pygmy loris venom. We conclude that the slow and pygmy lorises possess amongst the most complex venom system in extant animals, and while we have still a lot more to understand about their venom system, we are close to a breakthrough, particularly with current technological advances.

Postural behavior recognition of captive nocturnal animals based on deep learning: a case study of Bengal slow loris

The precise identification of postural behavior plays a crucial role in evaluation of animal welfare and captive management. Deep learning technology has been widely used in automatic behavior recognition of wild and domestic fauna species. The Asian slow loris is a group of small, nocturnal primates with a distinctive locomotion mode, and a large number of individuals were confiscated into captive settings due to illegal trade, making the species an ideal as a model for postural behavior monitoring. Captive animals may suffer from being housed in an inappropriate environment and may display abnormal behavior patterns. Traditional data collection methods are time-consuming and laborious, impeding efforts to improve lorises' captive welfare and to develop effective reintroduction strategies. This study established the first human-labeled postural behavior dataset of slow lorises and used deep learning technology to recognize postural behavior based on object detection and semantic segmentation. The precision of the classification based on YOLOv5 reached 95.1%. The Dilated Residual Networks (DRN) feature extraction network showed the best performance in semantic segmentation, and the classification accuracy reached 95.2%. The results imply that computer automatic identification of postural behavior may offer advantages in assessing animal activity and can be applied to other nocturnal taxa.

Training in the Dark: Using Target Training for Non-Invasive Application and Validation of Accelerometer Devices for an Endangered Primate (Nycticebus bengalensis)

Simple Summary

Recent advances in technology allow for the study of animal behaviours through indirect observations. This facilitates research on cryptic animals for which direct observations may miss a considerable portion of their activity. The validity of accelerometers in obtaining accurate animal behaviours, however, needs to be tested before collecting data in the wild. Modern zoos offer excellent opportunities for researchers to test field techniques in a safe setting. Here, we describe a non-invasive training program to attach an accelerometer to an individual Bengal slow loris at the Shaldon Wildlife Trust. This training took 39 15-min sessions and allowed for the attachment of the accelerometer for validation with reduced stress for the animal. We also collected videos to associate to accelerometer data to estimate the accuracy of accelerometers in identifying the behaviours of Bengal slow loris. The accuracy was above 80% with some of the behaviours that were clearly identified (e.g., resting: 99.8%), while others were more difficult to discern (e.g., suspensory walk, a locomotion behaviour, was discerned only 60.3% of times from other behaviours). The non-invasive training and accelerometer validation can be used on similar species before using accelerometers in the wild.

Abstract

Accelerometers offer unique opportunities to study the behaviour of cryptic animals but require validation to show their accuracy in identifying behaviours. This validation is often undertaken in captivity before use in the wild. While zoos provide important opportunities for trial field techniques, they must consider the welfare and health of the individuals in their care and researchers must opt for the least invasive techniques. We used positive reinforcement training to attach and detach a collar with an accelerometer to an individual Bengal slow loris (Nycticebus bengalensis) at the Shaldon Wildlife Trust, U.K. This allowed us to collect accelerometer data at different periods between January–June 2020 and January–February 2021, totalling 42 h of data with corresponding video for validation. Of these data, we selected 54 min where ten behaviours were present and ran a random forest model. We needed 39 15-min sessions to train the animal to wear/remove the collar. The accelerometer data had an accuracy of 80.7 ± SD 9.9% in predicting the behaviours, with 99.8% accuracy in predicting resting, and a lower accuracy (but still >75% for all of them apart from suspensory walk) for the different types of locomotion and feeding behaviours. This training and validation technique can be used in similar species and shows the importance of working with zoos for in situ conservation (e.g., validation of field techniques).

The sticky tasty: the nutritional content of the exudativorous diet of the Javan slow loris in a lowland forest

Plant exudates are an important food source for many primates. The Critically Endangered Javan slow loris (Nycticebus javanicus) was previously found to prefer Acacia decurrens exudate in an anthropogenically disturbed site, while its feeding habits in secondary natural forest remain unknown. Knowledge of the chemical characteristics of the plant exudates that Javan slow lorises consume is limited, especially with respect to those that they feed on in natural forests. As plant exudates may contain plant secondary metabolites (PSM), which are considered unpalatable in high concentrations, differences in PSM composition may drive feeding preferences. This research aims firstly to confirm exudate consumption by the Javan slow loris in a lowland tropical forest in Central Java, and secondly to identify the chemical characteristics of the exudates consumed. We followed wild slow lorises in Kemuning Forest, Central Java and observed their behaviour. We investigated the gum-producing trees that were utilized by the slow lorises by tapping the exudates and examining their nutritional and PSM contents. We found that exudates are the predominant food source for the Javan slow loris in this lowland forest, and that their nutritional contents are similar to those of exudates consumed by lorises in anthropogenically disturbed areas. Significant differences in polysaccharide and flavonoid contents were found between consumed and unconsumed exudates. Knowledge of the diet of the Javan slow loris is crucial to its conservation, and our findings confirm the importance of exudates in its diet. We also highlight the need to preserve natural slow loris habitat, and to manage the diets of these species in captivity. The results of this study indicate that plant exudates should constitute a significant portion of the diet of captive slow lorises, and that the presence of exudate-producing trees is vital in areas into which slow lorises are to be translocated.

Aposematic signaling and seasonal variation in dorsal pelage in a venomous mammal

In mammals, colouration patterns are often related to concealment, intraspecific communication, including aposematic signals, and physiological adaptations. Slow lorises (Nycticebus spp.) are arboreal primates native to Southeast Asia that display stark colour contrast, are highly territorial, regularly enter torpor, and are notably one of only seven mammal taxa that possess venom. All slow loris species display a contrasting stripe that runs cranial-caudally along the median sagittal plane of the dorsum. We examine whether these dorsal markings facilitate background matching, seasonal adaptations, and intraspecific signaling. We analyzed 195 images of the dorsal region of 60 Javan slow loris individuals (Nycticebus javanicus) from Java, Indonesia. We extracted greyscale RGB values from dorsal pelage using ImageJ software and calculated contrast ratios between dorsal stripe and adjacent pelage in eight regions. We assessed through generalized linear mixed models if the contrast ratio varied with sex, age, and seasonality. We also examined whether higher contrast was related to more aggressive behavior or increased terrestrial movement. We found that the dorsal stripe of N. javanicus changed seasonally, being longer and more contrasting in the wet season, during which time lorises significantly increased their ground use. Stripes were most contrasting in younger individuals of dispersal age that were also the most aggressive during capture. The dorsal stripe became less contrasting as a loris aged. A longer stripe when ground use is more frequent can be related to disruptive colouration. A darker anterior region by younger lorises with less fighting experience may allow them to appear larger and fiercer. We provide evidence that the dorsum of a cryptic species can have multimodal signals related to concealment, intraspecific communication, and physiological adaptations.

Risky Business: The Function of Play in a Venomous Mammal-The Javan Slow Loris (Nycticebus javanicus)

Immature mammals require opportunities to develop skills that will affect their competitive abilities and reproductive success as adults. One way these benefits may be achieved is through play behavior. While skills in developing use of tusks, antlers, and other weapons mammals have been linked to play, play in venomous animals has rarely been studied. Javan slow lorises (Nycticebus javanicus) use venom to aid in intraspecific competition, yet whether individuals use any behavioral mechanisms to develop the ability to use venom remains unclear. From April 2012 to December 2020, we recorded 663 play events and studied the factors influencing the frequency of play and the postures used during play in wild Javan slow lorises. Regardless of the presence of siblings, two thirds of play partners of young slow lorises were older and more experienced adults. Young lorises engaged in riskier behaviors during play, including using more strenuous postures and playing more in riskier conditions with increased rain and moonlight. We found that play patterns in immature lorises bear resemblance to venom postures used by adults. We suggest that play functions to train immature lorises to deal with future unexpected events, such as random attacks, as seen in other mammalian taxa with weapons. Given the importance of venom use for highly territorial slow lorises throughout their adult lives and the similarities between venom and play postures, we cannot rule out the possibility that play also prepares animals for future venomous fights. We provide here a baseline for the further exploration of the development of this unique behavior in one of the few venomous mammals.

Increased performance in juvenile baboons is consistent with ontogenetic changes in morphology

OBJECTIVES

In many primates, the greater proportion of climbing and suspensory behaviors in the juvenile repertoire likely necessitates good grasping capacities. Here, we tested whether very young individuals show near-maximal levels of grasping strength, and whether such an early onset of grasping performance could be explained by ontogenetic variability in the morphology of the limbs in baboons.

MATERIAL AND METHODS

We quantified a performance trait, hand pull strength, at the juvenile and adult stages in a cross-sectional sample of 15 olive baboons (Papio anubis). We also quantified bone dimensions (i.e., lengths, widths, and heights) of the fore- (n = 25) and hind limb (n = 21) elements based on osteological collections covering the whole development of olive baboons.

RESULTS

One-year old individuals demonstrated very high pull strengths (i.e., 200% of the adult performance, relative to body mass), that are consistent with relatively wider phalanges and digit joints in juveniles. The mature proportions and shape of the forelimb elements appeared only at full adulthood (i.e., ≥4.5 years), whereas the mature hind limb proportions and shape were observed much earlier during development.

DISCUSSION

These changes in limb performance and morphology across ontogeny may be explained with regard to behavioral transitions that olive baboons experience during their development. Our findings highlight the effect of infant clinging to mother, an often-neglected feature when discussing the origins of grasping in primates. The differences in growth patterns, we found between the forelimb and the hind limb further illustrate their different functional roles, having likely evolved under different ecological pressures (manipulation and locomotion, respectively).

Ontogeny of locomotion in mouse lemurs: Implications for primate evolution

The environment of juvenile primates is very challenging. They have to forage and move on the same substrates as adults do and escape the same predators, despite their immature state. In this study, we explore the developmental strategies that may provide effective locomotor abilities early in life. This could provide new insights into the selective pressures acting on juvenile primates and into evolution of primate locomotion. We conducted an ontogenetic study of 36 arboreal gray mouse lemurs from birth to adulthood (6 months of age). The investigated parameters were, for both limbs, (1) grasping behavior during locomotion (i.e., grip postures), (2) grasping performance (i.e., pull strength), and (3) motor coordination (i.e., rotarod test). Our results show that 8-day-old babies are able to climb substrates of various slopes and diameters outside of their nest. Although juveniles cannot successfully complete a motor coordination test before 30 days of age, young individuals display relative pull strengths that are very high or even on par with adults, guaranteeing stability on narrow substrates. These powerful grasps highlight the importance of the grasping function for these juveniles that are not carried and move independently on arboreal substrates shortly after their first week of life. Moreover, the pedal grasping provides a secure grasp on all substrates across ontogeny; however, manual secure grasps decrease during development, being highly used only shortly after birth on vertical and narrow substrates. These results first suggest different functional roles of the hands and feet, with the hind limbs ensuring body balance on the substrates, freeing the upper limbs for manipulation. They further show vertical and narrow branches to be especially challenging, requiring strong grasps, which suggests that they may drive the evolution of strong grasping abilities in primates.

The Toxicological Intersection between Allergen and Toxin: A Structural Comparison of the Cat Dander Allergenic Protein Fel d1 and the Slow Loris Brachial Gland Secretion Protein

Slow lorises are enigmatic animal that represent the only venomous primate lineage. Their defensive secretions have received little attention. In this study we determined the full length sequence of the protein secreted by their unique brachial glands. The full length sequences displayed homology to the main allergenic protein present in cat dander. We thus compared the molecular features of the slow loris brachial gland protein and the cat dander allergen protein, showing remarkable similarities between them. Thus we postulate that allergenic proteins play a role in the slow loris defensive arsenal. These results shed light on these neglected, novel animals.

Venom in Furs: Facial Masks as Aposematic Signals in a Venomous Mammal

The function of colouration in animals includes concealment, communication and signaling, such as the use of aposematism as a warning signal. Aposematism is unusual in mammals, and exceptions help us to understand its ecology and evolution. The Javan slow loris is a highly territorial venomous mammal that has a distinctive facial mask and monochromatic vision. To help understand if they use aposematism to advertise their venom to conspecifics or predators with different visual systems, we studied a population in Java, Indonesia. Using ImageJ, we selected colours from the facial masks of 58 individuals, converted RBG colours into monochromatic, dichromatic and trichromatic modes, and created a contrast index. During 290 captures, we recorded venom secretion and aggressiveness. Using Non-metric Multidimensional Scaling and generalised additive models for location, scale and shape, we found that young slow lorises differ significantly from adults, being both more contrasting and more aggressive, with aggressive animals showing fewer wounds. We suggest aposematic facial masks serve multiple purposes in slow lorises based on age. Change in colouration through development may play a role in intraspecific competition, and advertise toxicity or aggressiveness to competitors and/or predators in juveniles. Aposematic signals combined with intraspecific competition may provide clues to new venomous taxa among mammals.

Slow lorises (Nycticebus spp.) display evidence of handedness in the wild and in captivity

It has been suggested that strepsirrhines (lemurs, lorises, and galagos) retain the more primitive left-hand preference, whilst monkeys and apes more regularly display a right-hand preference at the individual-level. We looked to address questions of laterality in the slow loris (Nycticebus spp.) using spontaneous observations of 7 wild individuals, unimanual tests in 6 captive individuals, and photos of 42 individuals in a bilateral posture assessing handedness at the individual- and group-level. During the unimanual reach task, we found at the individual-level, only 4 slow lorises showed a hand use bias (R: 3, L: 1), Handedness index (HI) ranged from -0.57 to 1.00. In the wild unimanual grasp task, we found at the individual-level two individual showed a right-hand bias, the HI ranged from -0.19 to 0.70. The bilateral venom pose showed a trend toward a right-hand dominant grip in those photographed in captivity, but an ambiguous difference in wild individuals. There are many environmental constraints in captivity that wild animals do not face, thus data collected in wild settings are more representative of their natural state. The presence of right-handedness in these species suggests that there is a need to re-evaluate the evolution of handedness in primates.