In primates, infants are the special members in a society because they require extensive caretaking from adults. Intriguingly, in some species like chimpanzees, the appearance of an infant is clearly distinguished from that of an adult (e.g. white face) but in other species like bonobos, the appearance is relatively similar between infants and adults. In human previous studies, it is known that there is attentional bias for infants, while quite a few studies examined how adults perceive infants in non-human primates. This study examined viewing patterns for adult and infant individuals in chimpanzees and bonobos using a non-invasive eye-tracker. Fifteen chimpanzees and 6 bonobos participated in this study. We presented to them the pictures of mother-infant dyad of these species (both chimpanzees and bonobos) and an outgroup species (Japanese macaque). The total looking time for the adult and infant faces was analyzed. Chimpanzee participants showed significant infant looking bias to conspecifics. However, they showed marginally significant infant looking bias to the macaques, and neither adult nor infant looking bias to bonobos. The results suggest the existence of infant looking bias, which is supposed to help increasing provability of infant survival in chimpanzees. This bias is provably limited to own species. Conversely, bonobo participants showed significant adult looking bias to chimpanzees and macaques but not for bonobo. These results suggest that chimpanzees and bonobos have species-typical (but not species-general) interest to infants of own and other species.

Bodies are important social cues for animals. Humans show decreased performances in body recognition when bodies are inverted, compared to when they are upright. This inversion effect suggests the configural processing of bodies, which is different from the way used to process other objects. However, it is not known whether it exists in non-human primates. We tested seven chimpanzees using upright and inverted chimpanzee body stimuli and other stimuli in matching-to-sample tasks to examine the body inversion effect in order to understand their body processing. Experiment 1 used stimuli of chimpanzee bodies and houses. Experiment 2 used stimuli of intact bodies, bodies with blurred faces, and faces with blurred bodies. Experiment 3 used stimuli of intact bodies, bodies without faces, only faces, and body silhouettes. The chimpanzees showed the inversion effect to all intact body conditions, indicating the configural body processing. They also showed the inversion effect to faces with blurred bodies in Experiment 2 and to silhouettes in Experiment 3, suggesting the roles of faces and body contours in the inversion effect. The results suggest that chimpanzees use special cognitive processing to process bodies, which is different from the way they use for other objects, and that faces and body contours are important cues for body configural processing.

Many primate studies have investigated discrimination of individual faces within the same species. However, few studies have looked at discrimination between primate species faces at the categorical level, especially in chimpanzees. This study systematically examined the factors important for visual discrimination between primate species faces in chimpanzees, including: colour, familiarity and perceptual similarity. Five adult female chimpanzees were tested on their ability to discriminate identical and categorical (non-identical) images of different primate species faces in a series of touchscreen matching-to-sample experiments. After excluding effects of colour and familiarity, difficulty in discriminating between different species faces can be best explained by their perceptual similarity to each other. Categorical discrimination performance for unfamiliar, perceptually similar faces (gorilla and orangutan) was significantly worse than unfamiliar, perceptually different faces (baboon and capuchin monkey). Moreover, multidimensional scaling analysis of the image similarity data based on local feature matching revealed greater similarity between chimpanzee, gorilla and orangutan faces than between human, baboon and capuchin monkey faces. We conclude our chimpanzees appear to perceive similarity in primate faces in a similar way to humans. Information about perceptual similarity is likely prioritised over the potential influence of previous experience or a conceptual representation of species for categorical discrimination between species faces.

We examined sensitivity to efficiency of foraging in Japanese monkeys (Macaca fuscata) by using an experimental method at the feeding site of the Awajishima Group. Three feeding drawers which contained identical food reward, with different number of weights (condition1 and condition2) or in different food distance (condition3), were presented. Monkeys were allowed to pull each drawer to get each reward in any order. Twenty-five of 399 individuals have participated. The number of trials totaled 4079 during 14 days. We found that monkeys tended to choose the lightest or the nearest food first. These results show that monkeys adjusted their foraging strategies according to the cost of food reward. Sex and age contributed to the high selectivity of the first choice of the lowest load, which could be highly related with body weight. Interestingly, monkeys selected the remaining two choices with the same frequency in both condition1 and condition2. These results indicate that their adjustment of foraging strategies was also affected by the other factors such as social condition, since other individuals around them change constantly during the test sessions. In addition to the social factors, current results can be also discussed on the basis of “contrafreeloading”.

Several primate species exhibit red skin coloration that can communicated emotional state, dominance status, health condition, and fertility. When we are asked to picture colorful traits of female primates, we can easily think of the shiny sexual swelling of baboons, the geladas' “bleeding heart”, or the Japanese macaques' red mask. We usually don’t picture woman traits. Women seem to lack obvious and/or exaggerated traits of their fertility and/or quality. However, several studies have suggested that men may be able to pick up some facial indices of women fertility, such as variation in skin smoothness and brightness around ovulation. But none has investigated the possible role of the most colorful and appealing trait of the women face, i.e., lips. Women lips are subconsciously connected to fertility and beauty and women seem to compete with each other according to women and men's psychological standard of beauty. This study is the first attempt to investigate the relationship between women fertility, quality and lips coloration, i.e., whether darker/redder lips are associated with ovulation signaling or quality signaling (e.g. parity), from signal content to signal perception (men and women). This study aims to enhance our understanding of how female colorful sexual signals have evolved in non-human and human primates, using methods inspired from primate studies.

How animals interact and develop social relationships in face of sociodemographic and ecological pressures is of great interest. New methodologies, in particular Social Network Analysis (SNA), allow us to elucidate these types of questions. However, the different methodologies developed to that end and the speed at which they emerge make their use difficult. Moreover, the lack of communication between the different software developed to provide an answer to the same/different research questions is a source of confusion. The R package ‘Animal Network Toolkit’ (ANT) was developed with the aim of implementing in one package the different social network analysis techniques currently used in the study of animal social networks. Hence, ANT is a toolkit for animal research allowing among other things to: 1) measure global, dyadic and nodal networks metrics; 2) perform data randomization: pre- and post-network (node and link permutations); 3) perform statistical permutation tests. The package is partially coded in C++ for an optimal computing speed. The package gives researchers a workflow from the raw data to the achievement of statistical analyses, allowing for a multilevel approach: from the individual's position and role within the network, to the identification of interactional patterns, and the study of the overall network properties. Furthermore, ANT also provides a guideline on the SNA techniques used: 1) from the appropriate randomization technique according to the data collected; 2) to the choice, the meaning, the limitations and advantages of the network metrics to apply, 3) and the type of statistical tests to run.

Bitter taste plays an important role in avoiding toxin ingestion and inducing innate avoidance behaviors. Difference in bitter taste sensitivity might reflect species-specific diets during mammalian evolution. In addition to diet, it was recently reported that the receptors are involved in the immuno-system against bacteria and parasites. TAS2R38 has been studied for bitter taste sensitivity, especially for bitter compound Phenylthiocarbamide (PTC). Here, we report characterization of TAS2R38 in four species of Sulawesi macaque, M. hecki (N: 13), M. tonkeana (N: 12), M. nigrescens (N: 5) and M. nigra (N: 14). We conducted behavioral experiment on PTC acceptance and later functional analysis on amino acid residue(s) of TAS2R38 responsible for low bitter taste sensitivity. Our result shows that both M. tonkeana and M. nigra were found with “non-taster” but exhibited different pattern in genetic aspect. Amino acid changes at position 117, 130, 134 of M. tonkeana, whereas one base insertion caused early stop codon at site 178 of M. nigra, leading to non-taster phenotype separately. This finding might give a clue for clarifying evolutionary relationship and dietary habits among the four species. In addition, it will help to elucidate the ecological, evolutionary, and neurobiological aspects of bitter taste perception of primates, as bitter taste may be related to the plants they consume.

On a global scale, urban development is the fastest growing form of land use and has led to more severe human-wildlife conflict in recent years. Noting the role of gut microbiome in host physiology like nutrition and immune system, it is thus essential to understand how human-wildlife conflict can affect animals’ gut microbiome. This study therefore set out to assess the anthropogenic influence on gut microbiome of Japanese macaques and the possibility of using gut microbiome as indicator for anthropogenic influence. Using 16S rRNA gene sequencing, we described the microbiome composition of Japanese macaques Macaca fuscata experiencing different human disturbance levels - captive, provisioned, crop-raiding and wild. For alpha diversity, our result showed that observed richness of gut microbiome did not differ significantly between disturbance levels but between collection sites. For beta diversity, captive populations harbored the most distinctive gut microbiome composition, and had greatest difference with wild populations. Whereas for provisioned and crop-raiding groups, the macaques exhibited intermediate microbiome between wild and captive. Bacterial taxa from phyla Firmicutes, Bacteroidetes and Cyanobacteria demonstrated shift in abundance along the disturbance level. Specifically, we found Firmicutes to Bacteroidetes ratio and Cyanobacteria abundance elevated in wild macaques. In summary, this study revealed the flexibility of gut microbiome of Japanese macaques and the possibility of using gut microbiome profile in assessing the anthropogenic effect to non-human primates.

Southeast Asian archipelago is the home of a wide range of endemic gibbon species. While human cranial morphometic variation based on insularity and provinciality is extensively studied, little is known about the pattern on other insular non-human hominoid species. Two gibbon species of Hylobates lar and Hylobates agilis crania found in both mainland and island were examined to be compared to all gibbon species throughout Southeast Asia. The exterior outline of 22 lateral and 12 dorsal three-dimensional homologous landmarks were digitized on 141 crania. The landmark data were first subjected to generalize Proscustes Analysis, followed by principal component analysis. Wireframe diagram demonstrates that compared to crania of the mainland, the lateral crania of the island in both hylobates species displays a generally convex anteromedial corner on parietal bones with the shift of the junction of coronal and sagittal sutures (BRG) anteriorly and the inion (INI) ventrally. The dorsal view exhibits the strong shift of orbital surface of sphenoid bone (SFT) medially on the island crania. This investigation contributes as the preliminary study of insularity of non-human primate of Southeast Asia.

The guenons are a recent primate radiation that exhibit high degrees of sympatry, and commonly form mixed-species groups. Hybridization is possible, yet rare in most populations. Guenons have species-specific colorful face patterns hypothesized to function as signals used in species discrimination. Here, consistent with this, I present our studies showing that guenon faces exhibit character displacement, with species being more facially distinctive specifically from the species that they overlap with geographically. I then show that species can be reliably classified by these facial patterns, including specific components of these faces, and present machine classification data that reveal the specific regions of faces that are diagnostic for species discrimination for each species. I go on to present new experimental data testing these machine classification results back to live guenons, which show that they do indeed focus primarily on those regions when presented with the faces of different species. Collectively, our results suggest that guenon face patterns have evolved as mate discrimination signals that facilitate reproductive isolation between species. Our research adds to our understanding of the relationship between reproductive isolation and phenotypic diversity among the primates.

Through their senses, animals sample information from the external environment to detect and assess foods. Studying the sensory behaviors of frugivores provides insight into the interactions between plants and animals, and promotes understanding of evolutionary processes shaping sensory systems. It is well known that fruit traits—including color, size, odor, and softness—often change during the ripening process. However, there is a dearth of data on whether changes in each of these modalities are equally reliable in revealing shifts in fruit nutritional value, and which types of information animals use to guide their foraging strategies. Here, we integrate behavioral observations from a 12-month study of white-faced capuchins (Cebus imitator) with visual (size, shape, color) olfactory (volatile organic compounds—VOCs), haptic (elastic modulus), and nutritional data from 14 species of fruits sampled across ripeness stages. We find: 1) variation among plant species in how well changes in fruit softness, color, size, and odor correlate with nutritional changes; 2) that primate behavior maps predictably onto this variation; 3) that color and size are typically the least reliable cues of ripeness. These results help explain why primates also sniff and squeeze fruits that change color as they ripen, the smaller than expected difference in foraging efficiency between “colorblind” and “color-normal” monkeys, and highlight a role for color in long-distance signaling by plants to attract foraging animals. This study contributes to knowledge about the foraging cues available to primates and other frugivores, and how multiple sensory modalities are integrated to inform food selection.