Deep learning for automatic facial detection and recognition in Japanese macaques: illuminating social networks.

Individual identification plays a pivotal role in ecology and ethology, notably as a tool for complex social structures understanding. However, traditional identification methods often involve invasive physical tags and can prove both disruptive for animals and time-intensive for researchers. In recent years, the integration of deep learning in research has offered new methodological perspectives through the automatisation of complex tasks. Harnessing object detection and recognition technologies is increasingly used by researchers to achieve identification on video footage. This study represents a preliminary exploration into the development of a non-invasive tool for face detection and individual identification of Japanese macaques (Macaca fuscata) through deep learning. The ultimate goal of this research is, using identification done on the dataset, to automatically generate a social network representation of the studied population. The current main results are promising: (i) the creation of a Japanese macaques' face detector (Faster-RCNN model), reaching an accuracy of 82.2% and (ii) the creation of an individual recogniser for the Kojima Island macaque population (YOLOv8n model), reaching an accuracy of 83%. We also created a Kojima population social network by traditional methods, based on co-occurrences on videos. Thus, we provide a benchmark against which the automatically generated network will be assessed for reliability. These preliminary results are a testament to the potential of this approach to provide the scientific community with a tool for tracking individuals and social network studies in Japanese macaques.

Differential leg and trunk operation during skipping without and with hurdles in bipedal Japanese macaque.

When locomoting bipedally at higher speeds, macaques preferred unilateral skipping (galloping). The same skipping pattern was maintained while hurdling across two low obstacles at the distance of a stride within our experimental track. The present study investigated leg and trunk joint rotations and leg joint moments, with the aim of clarifying the differential leg and trunk operation during skipping in bipedal macaques. Especially at the hip, the range of joint rotation and extension at lift off was larger in the leading than in the trailing leg. The flexing knee absorbed energy and the extending ankle generated work during each step. The trunk showed only minor deviations from symmetry. Hurdling amplified the differences and notably resulted in a quasi-elastic use of the leading knee and in an asymmetric operation of the trunk.

Mineral acquisition of Japanese macaques: Contents in the foods, digestibility, and sodium-provisioning experiment.

Minerals provide micronutrients that function in various ways in the body, and they are necessary for the survival of animals. In this study, we first compared the mineral content of foods of wild Japanese macaques in lowland Yakushima with that of monkey chow used for many years to feed captive macaques and specifically formulated to obtain good health in captive macaques (National Research Council [NRC] recommendations). Second, we clarified the mineral balance in captive individuals when feeding them monkey chow to clarify the digestibility/bioavailability of the minerals. Third, we investigated the physiological response when we experimentally increased sodium intake. In the lowland of Yakushima, which is in the vicinity (<800 m) of the coast, animals, fungi, and mature leaves had high sodium contents compared with NRC recommendations. The calcium contents of mature leaves and animals were higher than the NRC recommendations. The overall mineral intake in this population was lower than that in the captive animals for calcium, phosphorus, sodium, and iron, while similar for magnesium and higher in potassium. Patterns in the intake and excretion of minerals indicated that excretion was mostly from urine and not from feces, and apparent digestibility was high for sodium. This tendency was opposite for calcium, magnesium, and phosphorus and intermediate for potassium. A sodium-provisioning experiment showed that fecal aldosterone concentration remained low in both control and sodium-provisioning conditions so the macaques do not need reabsorb sodium in the kidneys. Therefore, sodium content in the monkey chow, which is slightly lower than the NRC recommendation, seemed high enough so that the macaques could avoid the need to reabsorb sodium in the kidneys. We advocate similar studies for other primate populations or species to better understand the role of mineral concentrations on food selection and to identify potential mineral deficiencies.

Winter diet of Japanese macaques from Chubu Sangaku National Park, Japan incorporates freshwater biota.

The Japanese macaque (Macaca fuscata) is native to the main islands of Japan, except Hokkaido, and is the most northerly living non-human primate. In the Chubu Sangaku National Park of the Japanese Alps, macaques live in one of the coldest areas of the world, with snow cover limiting the availability of preferred food sources. Winter is typically a bottleneck for food availability potentially resulting in marked energy deficits, and mortality may result from famine. However, streams with groundwater upwelling flow during the winter with a constant water temperature of about 5 °C are easily accessible for Japanese macaques to search for riverine biota. We used metabarcoding (Cytochrome c oxidase I) of fecal samples from Japanese macaques to determine their wintertime diet. Here we provide the first robust evidence that Japanese macaques feed on freshwater biota, including brown trout, riverine insects and molluscs, in Chubu Sangaku National Park. These additional food sources likely aid their winter survival.

Chemogenetic inactivation reveals the inhibitory control function of the prefronto-striatal pathway in the macaque brain.

The lateral prefrontal cortex (LPFC) has a strong monosynaptic connection with the caudate nucleus (CdN) of the striatum. Previous human MRI studies have suggested that this LPFC-CdN pathway plays an important role in inhibitory control and working memory. We aimed to validate the function of this pathway at a causal level by pathway-selective manipulation of neural activity in non-human primates. To this end, we trained macaque monkeys on a delayed oculomotor response task with reward asymmetry and expressed an inhibitory type of chemogenetic receptors selectively to LPFC neurons that project to the CdN. Ligand administration reduced the inhibitory control of impulsive behavior, as well as the task-related neuronal responses observed in the local field potentials from the LPFC and CdN. These results show that we successfully suppressed pathway-selective neural activity in the macaque brain, and the resulting behavioral changes suggest that the LPFC-CdN pathway is involved in inhibitory control.

Interleukin-4 Promotes Tuft Cell Differentiation and Acetylcholine Production in Intestinal Organoids of Non-Human Primate.

In the intestine, the innate immune system excludes harmful substances and invading microorganisms. Tuft cells are taste-like chemosensory cells found in the intestinal epithelium involved in the activation of group 2 innate lymphoid cells (ILC2). Although tuft cells in other tissues secrete the neurotransmitter acetylcholine (ACh), their function in the gut remains poorly understood. In this study, we investigated changes in the expression of genes and cell differentiation of the intestinal epithelium by stimulation with interleukin-4 (IL-4) or IL-13 in macaque intestinal organoids. Transcriptome analysis showed that tuft cell marker genes were highly expressed in the IL-4- and IL-13-treated groups compared with the control, and the gene expression of choline acetyltransferase (ChAT), a synthesis enzyme of ACh, was upregulated in IL-4- and IL-13-treated groups. ACh accumulation was observed in IL-4-induced organoids using high-performance liquid chromatography-mass spectrometry (HPLC/MS), and ACh strongly released granules from Paneth cells. This study is the first to demonstrate ACh upregulation by IL-4 induction in primates, suggesting that IL-4 plays a role in Paneth cell granule secretion via paracrine stimulation.

Physiological variation in Japanese macaques (Macaca fuscata) housed in different outdoor cages evaluated using the metabolic profile test.

Captive primates require environmental enrichment to minimize physical and mental stress. However, only a few objective evaluations have been performed to assess environment-induced physiological variations in these animals. In this study, we evaluated the usage of the metabolic profile test (MPT) to assess the influences of the housing environment on the physiology of Japanese macaques. Five male macaques were housed in an old type of cage (old cage group), in which the macaques were exposed to wind (except for a shelter box), and four males were in a new -type of cage (new cage group), which had a sub-room with a waterer that was surrounded by insulating panels. Blood samples were collected bimonthly for a year from the two groups to determine the complete blood count and blood biochemistry. The increase in the body weight of the macaques in both groups was suppressed during the cold season. Furthermore, this suppression was more pronounced in the old cage group, suggesting that the energy expenditure was higher in the old cage group than in the new cage group. Moreover, the red blood cell count and hematocrit values were higher during the cold season in both cages than during the warm season, suggesting that macaques were dehydrated during the cold season. Dehydration tendency was more pronounced in the macaques from the old cage group than in those from the new cage group, suggesting that their water intake decreased during the cold season. Our results suggest that the MPT can be used to evaluate environment-induced physiological variations in Japanese macaques.

Japanese Macaques' (Macaca fuscata) sensitivity to human gaze and visual perspective in contexts of threat, cooperation, and competition.

Gaze sensitivity allows us to interpret the visual perspective of others, inferring their intentions and attentional states. In order to clarify the evolutionary history of this ability, we assessed the response of free-ranging Japanese macaques (Macaca fuscata) to human gaze in three contexts: threat (Experiment 1), cooperation (Experiment 2), and competition (Experiment 3). Subjects interpreted the direct gaze of an approaching human as a sign of threat, showing a greater flight initiation distance and more threats towards the human in this condition than when the human gazed in another direction. Subjects also adapted their behavior to the attentional cues of a human who gave them food, by for example moving into his visual field. However, the macaques did not seem to take the visual perspective of a human competing with them over food, as they failed to first retrieve the food that was not visible to the human (i.e., located behind an opaque barrier). Our results support the idea that Japanese macaques can respond to a human's gaze flexibly depending on the context. Moreover, they highlight the importance of studying animal behavior across different species and contexts to better understand the selective pressures that might have led to its evolution.

Tonic firing mode of midbrain dopamine neurons continuously tracks reward values changing moment-by-moment.

Animal behavior is regulated based on the values of future rewards. The phasic activity of midbrain dopamine neurons signals these values. Because reward values often change over time, even on a subsecond-by-subsecond basis, appropriate behavioral regulation requires continuous value monitoring. However, the phasic dopamine activity, which is sporadic and has a short duration, likely fails continuous monitoring. Here, we demonstrate a tonic firing mode of dopamine neurons that effectively tracks changing reward values. We recorded dopamine neuron activity in monkeys during a Pavlovian procedure in which the value of a cued reward gradually increased or decreased. Dopamine neurons tonically increased and decreased their activity as the reward value changed. This tonic activity was evoked more strongly by non-burst spikes than burst spikes producing a conventional phasic activity. Our findings suggest that dopamine neurons change their firing mode to effectively signal reward values in a given situation.

Forward dynamic simulation of Japanese macaque bipedal locomotion demonstrates better energetic economy in a virtualised plantigrade posture.

A plantigrade foot with a large robust calcaneus is regarded as a distinctive morphological feature of the human foot; it is presumably the result of adaptation for habitual bipedal locomotion. The foot of the Japanese macaque, on the other hand, does not have such a feature, which hampers it from making foot-ground contact at the heel during bipedal locomotion. Understanding how this morphological difference functionally affects the generation of bipedal locomotion is crucial for elucidating the evolution of human bipedalism. In this study, we constructed a forward dynamic simulation of bipedal locomotion in the Japanese macaque based on a neuromusculoskeletal model to evaluate how virtual manipulation of the foot structure from digitigrade to plantigrade affects the kinematics, dynamics, and energetics of bipedal locomotion in a nonhuman primate whose musculoskeletal anatomy is not adapted to bipedalism. The normal bipedal locomotion generated was in good agreement with that of actual Japanese macaques. If, as in human walking, the foot morphology was altered to allow heel contact, the vertical ground reaction force profile became double-peaked and the cost of transport decreased. These results suggest that evolutionary changes in the foot structure were important for the acquisition of human-like efficient bipedal locomotion.

A comparison of axial trunk rotation during bipedal walking between humans and Japanese macaques.

OBJECTIVES: Human walking involves out-of-phase axial rotations of the thorax and pelvis. It has long been believed that this rotational capability is a distinctive feature of the genus Homo. However, Thompson et al. (2015) showed that chimpanzees also counter-rotate their thorax relative to the pelvis during bipedal walking, which raised questions regarding the origins and development of this characteristic. In this study, we measured the axial rotation of the trunk during bipedal walking in humans and macaques to investigate if intra-trunk axial rotations are observed in non-hominoid primate species. MATERIALS AND METHODS: We collected three-dimensional trunk kinematic data during bipedal walking in six humans and five Japanese macaques. The human subjects walked on a treadmill, and the animal subjects walked on a 5-m runway. During walking, the positions of cluster markers, which defined trunk segments, were recorded by multiple video cameras. Segmental xyz coordinates were digitized, and transverse rotations were calculated using motion analysis software. RESULTS: Although trunk rotations in the global coordinate system were greater in macaques than in humans, the intra-trunk rotation and range of motion showed a similar pattern in the two species. CONCLUSIONS: Thoracic rotation relative to the pelvis during bipedal walking is not unique to the hominid lineage but rather a characteristic generated by the mechanical requirements of bipedal walking. The fact that the range of motion of counter rotation is similar in these species infers that an optimal range of rotation exists for bipedal walking.

Inter-individual variation in the diet within a group of Japanese macaques and its relationship with social structure investigated by stable isotope and DNA analyses.

We investigated individual variation in diet in relation to age-sex class and kin relationship in 28 of 40 members of a small group of wild Japanese macaques (Macaca fuscata). We used stable isotope ratios from hair as an index of individual dietary profiles, genetic relatedness as an index of kin relationship, and mitochondrial DNA (mtDNA) haplotype as a marker of being an immigrant or native member of the group. The range of carbon and nitrogen stable isotope ratios from hair of individual macaques (δ13C: -24.1‰ to -22.6‰, δ15N:3.8-5.5‰), which reflected their diet over a period of ~ 6 months, implied small individual variation in diet. The results of PERMANOVA implied that there were no significant effects of age class, sex, or mtDNA haplotype on hair stable isotope ratios between individuals, or on the variation in individual diet. However, the isotope values of males with mtDNA haplotypes that differed from those of the native females appeared to differ from those of other group members, which implies that immigrant males might have had a different diet profile from that of native group members. Furthermore, there was a weak correlation trend between genetic relatedness and differences in stable isotope ratios between pairs of individuals. Differences in stable isotope values were more marked in pairs with a more distant genetic relationship. This implies that within the group, closely related kin tended to forage together to avoid competing for food. However, this effect might have been weak because the size of the group was small relative to the size of the food patches, thereby reducing competition.

Ranging patterns of Japanese macaques in the coniferous forest of Yakushima: Home range shift and travel rate.

Ranging is one of the most important behavioral adaptations for coping with seasonally fluctuating food and thermal conditions. We studied the ranging patterns, in particular home range shift and travel rate of Japanese macaques (Macaca fuscata) in the coniferous forest of Yakushima by tracking a group for 17 months. We also supplemented our data with records collected every August over a 5-year annual census. The macaque group used the eastern part of their home range from May to September and the western part during the rest of the year. The eastern part of the home range was largely primary forest in the national park, and the altitude was higher than in the western part. When they used the western part, the macaques ate more herbs and fruits from small-sized trees, the availability of which was higher in the logged forest. This east-west home range shift occurred repeatedly over multiple years. A neighboring group occupied the western part of the focal group's home range in summer, which the focal group did not use in that season. Both temperature and diet affected seasonal changes in the monthly average travel rate. Animals need more energy for thermoregulation when the temperature is low, so the macaques decreased their ranging efforts to save energy at times of low temperature. They increased their ranging distance to eat fungi, since their encounters with this food would increase with the total distance walked. They also increased their travel rate when eating flowers, which had lower food patch (tree) density than other foods such as fruits. The data supported the hypothesis that the macaques capitalize on habitat heterogeneity in a seasonally fluctuating habitat by shifting their home range and modifying their travel rate.

Variation in Adult Male-Juvenile Affiliative Behavior in Japanese Macaques (Macaca fuscata).

Adult males of some primate species are known to positively interact with juveniles. In cases where paternal certainty is high, these behaviors have been largely attributed to the paternal investment hypothesis. Males have also been observed to interact with nonkin juveniles, which has often been explained in terms of mating effort. Here, we examined variation in adult male-juvenile affiliation in semi-free ranging Japanese macaques (Macaca fuscata) at the Oregon National Primate Research Center against possible influencing factors such as age, dominance rank, and female affiliation, and we also tested for fitness benefits. We conducted 154 h of focal observations of 14 adult males from June to September 2018. Males differed significantly in their rate of juvenile-directed affiliation, but not in their fitness in terms of number of offspring. There was a significant positive correlation between rank and age in the group, indicating that, in this group, rank does not conform to the classic inverted-U pattern observed elsewhere in this species. Although there was a significant positive correlation between rank and juvenile-directed affiliation, the highest-ranking male had few offspring and exhibited little juvenile-directed affiliation. These results suggest little to no preliminary support for either the paternal investment or mating effort hypotheses as explanations for juvenile-directed affiliation. This study suggests that there are multiple behavioral strategies for older males that may influence reproductive success.

Comparative Gross Anatomy of the Forelimb Arteries of the Japanese Monkey (Macaca fuscata) and a Comparative Pattern of Forelimb Arterial Distribution in Primates.

Macaca fuscata displays characteristic behaviours, such as stone handling, locomotor behaviour, gait position, and intermittent bipedalism. Differences in characteristic behaviours among primate species/genera could be explained by anatomical details of the body. However, the anatomical details have not been well studied in Macaca fuscata. Arterial models could be one of the anatomical bases for the phylogenetic and functional differences among species, since the arterial supply could be associated with the muscular performance, especially locomotor behaviour. In this study, five thoracic limbs of Macaca fuscata adults were dissected to analyse the vessels. Patterns of arterial distribution in the thoracic limbs of Macaca fuscata were compared with those in other primates. The results indicated that the arterial distribution in the Japanese monkeys was more similar to those in Macaca mulatta and Papio anubis, which is consistent with phylogenetic similarities. However, compared with Papio anubis and other macaques, there were anatomical differences in several points, including (1) the origin of the common, anterior, posterior circumflex, and profunda brachii, and (2) the origins of the collateralis ulnaris artery. The comparative anatomy of the arteries in the forelimb of Macaca fuscata, along with the anatomical studies in other primates, indicated characteristic patterns of brachial artery division and the number of the palmar arches in primates, which is consistent with the phylogenetic division among New World primates, Old World primates, and apes.

Topographic distinction in long-term value signals between presumed dopamine neurons and presumed striatal projection neurons in behaving monkeys.

Nigrostriatal dopamine (DA) projections are anatomically organized along the dorsolateral-ventromedial axis, conveying long-term value signals to the striatum for shaping actions toward multiple future rewards. The present study examines whether the topographic organization of long-term value signals are observed upon activity of presumed DA neurons and presumed striatal projection neurons (phasically active neurons, PANs), as predicted based on anatomical literature. Our results indicate that DA neurons in the dorsolateral midbrain encode long-term value signals on a short timescale, while ventromedial midbrain DA neurons encode such signals on a relatively longer timescale. Activity of the PANs in the dorsal striatum is more heterogeneous for encoding long-term values, although significant differences in long-term value signals were observed between the caudate nucleus and putamen. These findings suggest that topographic DA signals for long-term values are not simply transferred to striatal neurons, possibly due to the contribution of other projections to the striatum.

Fermentation Ability of Gut Microbiota of Wild Japanese Macaques in the Highland and Lowland Yakushima: In Vitro Fermentation Assay and Genetic Analyses.

Wild Japanese macaques (Macaca fuscata Blyth) living in the highland and lowland areas of Yakushima are known to have different diets, with highland individuals consuming more leaves. We aim to clarify whether and how these differences in diet are also reflected by gut microbial composition and fermentation ability. Therefore, we conduct an in vitro fermentation assay using fresh feces from macaques as inoculum and dry leaf powder of Eurya japonica Thunb. as a substrate. Fermentation activity was higher for feces collected in the highland, as evidenced by higher gas and butyric acid production and lower pH. Genetic analysis indicated separation of highland and lowland in terms of both community structure and function of the gut microbiota. Comparison of feces and suspension after fermentation indicated that the community structure changed during fermentation, and the change was larger for lowland samples. Analysis of the 16S rRNA V3-V4 barcoding region of the gut microbiota showed that community structure was clearly clustered between the two areas. Furthermore, metagenomic analysis indicated separation by gene and pathway abundance patterns. Two pathways (glycogen biosynthesis I and D-galacturonate degradation I) were enriched in lowland samples, possibly related to the fruit-eating lifestyle in the lowland. Overall, we demonstrated that the more leaf-eating highland Japanese macaques harbor gut microbiota with higher leaf fermentation ability compared with the more fruit-eating lowland ones. Broad, non-specific taxonomic and functional gut microbiome differences suggest that this pattern may be driven by a complex interplay between many taxa and pathways rather than single functional traits.

Extractive foraging on hard-shelled walnuts and variation of feeding techniques in wild Japanese macaques (Macaca fuscata).

Extractive foraging is considered a key selective pressure for the evolution of primate cognitive abilities-the extractive foraging hypothesis. Although tool-use and substrate-use are representatives of the foraging strategy, some primates engage in extractive foraging without external objects. Manual processing skills of prickly foods have been described in some species, whereas there are few studies on other type of food defenses. Here, I describe extractive foraging of hard-shelled walnuts by wild Japanese macaques (Macaca fuscata), focusing on whether they accomplish the tasks only by their physical strength or require manual and/or oral processing skills to crack open the walnut shells. The study subjects comprised all members of troop B1 and three nontroop males in Kinkazan Island, Japan. Walnut feeding was observed during the main walnut seasons (September-December) when the troop visited walnut patches for 79 days in 2 years. I categorized the walnut feeding behavior into complete cracking and partial cracking. The number of times the five behavioral elements in the cracking stage occurred were counted from complete cracking. All six adult males and 11 of the 17 adult/adolescent females showed complete cracking, while the remaining females were never observed exhibiting this activity, despite their physical maturity. I observed four clearly distinguishable cracking methods during walnut feeding in the 17 subjects. The compositions of five behavioral elements were different in each method. These results suggest that walnut feeding by Japanese macaques is not only by brute force but requires the acquisition of at least one of four cracking methods for the achievement of complete cracking. In particular, females need to compensate for their physical inferiority by increasing walnut manipulations. To my knowledge, this is the first detailed description on feeding techniques in primates to overcome hard-shelled obstacles without the use of tools and even substrates.

Seasonal variation in energy balance of wild Japanese macaques (Macaca fucata yakui) in a warm-temperate forest: a preliminary assessment in the coastal forest of Yakushima.

Food scarcity is a major challenge for primates living in temperate forests, where food availability varies markedly among seasons. In Japanese macaques, which are exclusively distributed in temperate zones, the fat accumulation ability has been highlighted as an adaptation for survival during the lean season and for reproductive success. However, the knowledge of energetic strategies of Japanese macaques has been mainly derived from data on cool-temperate forests, where fallback foods comprise winter buds and bark. Data on Japanese macaques in warm-temperate forests where fallback foods comprise mature leaves are still lacking. We aimed to identify seasonal variations in energy balance and the relative importance of ingestion rates (dry matter intake per feeding time), energy content of the food, and feeding time in energy intake of Japanese macaques in the coastal forest of Yakushima. We estimated energy balance of 6-12 adult females from October 2012 to October 2013. We estimated energy intake based on the data on feeding behavior and energy content of the diet and calculated energy expenditure based on the previously established relationship between body mass and total energy expenditure. We also quantified urinary C-peptide, which is a non-invasive biomarker of energetic conditions. We demonstrated that energy balance was more positive in the fruit/seed-feeding period than in the mature-leaf-feeding and fruit/fungi-feeding periods and that ingestion rates were the most important component of energy intake. The present study suggests that the fat accumulation ability is an essential adaptation in Japanese macaques even in warm-temperate forests.

Variation in chewing efficiency of Yakushima Japanese macaque (Macaca fuscata yakui).

OBJECTIVES: Chewing efficiency plays an important role in the survival and distribution of primates. Yet, little is known about the intra-specific variation of chewing efficiency. The purpose of this study is to report the pattern of seasonal and regional variation in chewing efficiency among Yakushima Japanese macaques (Macaca fuscata yakui). MATERIALS AND METHODS: Fecal samples of Yakushima Japanese macaques were collected from lowland, highland and summit areas in Yakushima between July 2015 and March 2016 (n = 236). Using sieving analysis, we compared fecal particle size (dMEAN) and proportion of finest particles p(0) between different geographical areas and seasons. RESULTS: Seasonally, in the lowland zone, there was a non-significant decrease in dMEAN during spring, while p(0) was significantly higher during summer than it was during winter and spring. Regionally, dMEAN was higher in the summit zone than it was in other areas during autumn, while p(0) was also higher in the summit zone. CONCLUSIONS: While seasonal variation in dMEAN can be explained by the reported difference in the proportions of food categories in diet between seasons, its influence is mitigated, possibly by the selective feeding of less mechanically challenging parts in each category. Regional variation in dMEAN and p(0) may be the results of bamboo consumption in this area. Combining our data with studies that focus on seasonal and regional variations of food properties or gut microbes might provide a better understanding of the relation between diet, chewing and digestion in Yakushima macaques.