Allen's rule first published in 1877 predicts ecogeographical anatomical variation in appendage proportions as a function of body temperature regulation. Since then this phenomenon has been tested in a variety of animal species. In macaques, relative tail length (RTL) is one of the most frequently measured appendages to test Allen's rule. To date, these studies have relied mostly on randomly collected museum specimens or the invasive and time consuming capturing of free-ranging individuals. To augment sample size, and lessen these logistical limitations, we designed and validated a novel non-invasive technique using digitalized photographs processed on LibreCAD, an open source 2D-CAD application. This was used to generate pixelated measurements to calculate a RTL equivalent, the Tail to Trunk Index (TTI) = tail (tail base to anterior tip) pixel count / trunk (neck to tail base) pixel count X 100). The TTI of 259 adult free-ranging toque macaques (Macaca sinica) from 36 locations between 7 and 2087 m above sea level (m. a. s. l.) were used in the analysis. Samples were collected from all three putative subspecies (M. s. sinica, aurifrons and opisthomelas), at locations representing all altitudinal climatic zones where they are naturally distributed. These data were used to test Allen's rule, predicting that RTL decreases with increasing altitude. Our results strongly supported this prediction. There was also a statistically significant, negative correlation between elevation and annual average temperature. The best predictor for the TTI index was elevation. This non-invasive method provides a means for quick morphometric assessment of relative body proportions, applicable for use even on unhabituated free-ranging animals, widening the range of materials available for research studying morphological characteristics and their evolution in primates.

Previous studies have shown that humans experience negative emotions (i.e., empathic pain) when observing pain in others. We investigated psycho-physiological reactions to others’ injury and pain in two species of great apes: six chimpanzees (Pan troglodytes) and six bonobos (Pan paniscus). Specifically, we used infrared thermal imaging to measure their nasal skin temperature when they were viewing a real-life theatrical demonstration by a human experimenter. Previous studies suggest that reduced nasal skin temperature is a characteristic of arousal, particularly arousal associated with negative valence. First, we presented apes with a realistic injury: a familiar human experimenter with a prosthetic wound and artificial running blood. Chimpanzees, especially adult females, exhibited a greater nasal temperature reduction in response to injury compared with the control stimulus, whereas such a clear difference was not observed in bonobos. Second, apes were presented with a familiar experimenter who stabbed their (fake) thumb with a needle, with no running blood, a situation that may be more challenging in terms of understanding the cause of pain. Apes did not physiologically distinguish this condition from the control condition. Lastly, apes were presented with a human experimenter who hurt themselves accidentally and expressed pain explicitly by behavioral cues. Again, apes did not physiologically distinguish this condition from the control condition. These results suggest that apes can infer the cause of pain from contextual cues, but have difficulty in understanding unfamiliar situations.

This study aims to investigate how chimpanzees and children process bodies of other species and which kinds of cues they use, including embodied and visual experience. Previous research has found that human adults show the inversion effect to bodies of conspecifics and other species that they have visual or embodied expertise with, that is, they are better at recognizing the bodies when they are upright than inverted. The inversion effect is not found for other objects. In this study, we tested the inversion effect in seven adult chimpanzees and 33 children (43-75 months old). For chimpanzees, we used stimuli of crawling humans, horses (they have no visual experience with them but they share the quadrupedal postures), bipedal humans with visually familiar postures and unfamiliar postures. For children, we used stimuli of humans (conspecific), chimpanzees (not familiar), horses (familiar), and houses (other objects). They did recognition tasks with upright and inverted stimuli on touch screen computers. For chimpanzees, they showed the inversion effect to crawling humans, horses, and bipedal humans with familiar postures. It suggests that they use both embodied and visual experience when processing other species' bodies. For children, they showed the inversion effect to humans, chimpanzees and horses. It suggests that children are more sensitive to visual experience cues than chimpanzees, because they have limited visual experience with chimpanzee bodies but still showed the expert-only inversion effect. There was no change in the inversion effect with age, suggesting that the use of visual experience in children is stable in the pre-school phase.

Chewing, as an intermediate step between food handling and chemical digestion in the whole nutrition intake process, is one of the initial steps that deals with the mechanical defenses of food. It has been associated with the fitness of mammals by influencing digestive efficiency. As a major mechanical defense of plant, toughness is one of the most prominent extrinsic factors that limits chewing efficiency in primates. This study aims to clarify the seasonal variation of food fracture toughness and chewing efficiency in Yakushima Japanese macaque (Macaca fuscata yakui). We collected feeding behavior data and fecal samples in Yakushima lowland. Food fracture toughness was measured with a rheometer. Fecal particle size was measured by sieving analysis to show the variation in chewing efficiency. Here, we report the preliminary results about the seasonal and age-sex related variation in dietary fracture toughness and fecal particle size. And we would like to discuss the relationship of food mechanical properties and chewing efficiency.

Bitter taste plays an important role in avoiding ingestion of toxins and resisting bacteria and parasites, which might evolve to reflect species-specific diets during mammalian evolution. Bitter taste receptors (TAS2Rs) mediate the bitter perception in mammals. We investigated the polymorphism of a well-studied bitter taste receptor TAS2R38, protein for the bitter Phenylthiocarbamide (PTC), in four allopatric species (M. hecki (N: 16), M. tonkeana (N: 12), M. nigrescens (N: 11) and M. nigra (N: 15)) of Sulawesi macaques in Sulawesi Island, Indonesia. In most cases, individuals are sensitive to PTC. We observed all individuals of M. hecki are sensitive to PTC while some individuals of M. tonkeana, M. nigra and M. nigrescens showed low sensitive to PTC. Determining TAS2R38 sequence, we found truncated TAS2R38 led to no sensitivity of PTC in M. nigra and M. nigrescens. Functional protein assay showed substitution on three amino acid sites are responsible for low sensitivity in M. tonkeana. Phylogenetic analysis showed TAS2R38 of Sulawesi macaques is derived from M. nemestrina and the low-sensitive allele in M. tonkeana is shared with M. nemestrina. The non-sensitive alleles occurred independently in M. nigra and M. nigrescens after speciation. The low-sensitive alleles in M. tonkeana might express apparently intact TAS2R38 receptor, with low response to PTC. The intact low-sensitive alleles may respond to other bitter compounds. These results revealed species difference on bitter taste; however, whether these differences were resulted from local adaptation need to be studied.

Group living is beneficial for individuals in a group, but also comes with costs. One such cost is the increased possibility of pathogen transmission. Yet, most research that focuses on social transmission in primates has done so with only subsets of the group (e.g. adults or even adult females), which will influence the results and their interpretation. With this in mind, we aimed to test (i) whether social interactions or proximity mediate the spread of intestinal parasites in primate groups, and (ii) whether work that includes only subsets of a group might produce biased results. To test these hypotheses, we investigated the relationship between social network centrality and intestinal parasite infection intensity in a group of Japanese macaques (Macaca fuscata), using both empirical and simulated data. We used social network analysis on data collected over two months on Koshima to relate indices of network centrality to an index of parasite infection intensity (fecal egg counts: FEC). We then ran a series of knock-out simulations to test the effect(s) of missing data on the observed relationship. General linear mixed models showed that social network centrality was positively associated with infection by nodular worm (Oesophagostomum aculeatum) in the complete observed data set but including only subsets of the group (e.g. adult females or random subsets of the group) can yield false negative results; though a juvenile only network retains the positive association between sociality and infection. Results suggest that social interactions or shared proximity can mediate the spread of some intestinal parasites, but researchers that only focus on subsets of their study groups, or where missing data may be an issue, must interpret their results with caution. This work introduces important methodological considerations for research into the dynamics of social transmission, and not just for infectious disease.