<p>Supplemental information</p><p>Ethics statement</p><p>Animal husbandry and research complied with the international standards in accordance with the recommendation of the Weatherall report “The use of non-human primates in research” and the local guidelines which are strictly adhered to the national laws of Japan or Germany [KS: Primate Research Institute “Guide for the Care and Use of Laboratory </p><p>Primates 3rd Edition”, Wildlife Research Center “Guide for the Animal Research Ethics”] </p><p>[WKPRC: “EAZA Minimum Standards for the Accommodation and Care of Animals in Zoos and Aquaria”, “WAZA Ethical Guidelines for the Conduct of Research on Animals by Zoos and Aquariums”, “Guidelines for the Treatment of Animals in Behavioral Research and </p><p>Teaching” of the Association for the Study of Animal Behavior (ASAB)]. The study protocol was approved by the institutional committee of Wildlife Research Center (No. WRC-</p><p>2014KS001A) and Max-Planck Institute for Evolutionary Anthropology.</p><p>Table S 1: Participant information. Also shown are the participants for salivary cortisol and</p><p>ECG analysis.</p><p>Facility Sex Age Rearing history Name Cortisol ECG</p><p>Experiment 1 MPI F 39 Nursery Riet</p><p>MPI M 9 Mother Kofi Yes</p><p>MPI F 9 Mother Kara Yes</p><p>MPI M 13 Mother Lome Yes</p><p>MPI M 9 Mother Lobo Yes MPI M 39 Nursery Robert Yes</p><p>MPI F 38 Nursery Fraukje Yes</p><p>MPI M 20 Mother Frodo</p><p>MPI F 33 Nursery Drien</p><p>Experiment 2 KS F 18 Nursery Mizuki Yes</p><p>KS F 6 Nursery Hatsuka</p><p>KS F 9 Mother Natsuki</p><p>Meal-induced decrease in nasal temperature</p><p>In preliminary sessions (without presenting any stimulus) to establish the thermal measurement in KS (Experiment 2), we were initially giving the chimpanzees several hundred grams of fruits and vegetables (their daily lunch) to keep them on the chair. In these preliminary recordings, we found that quick consumption of large amount of foods </p><p>(e.g. one banana) lowered their nasal temperature to a considerable degree (1-2 °C). This is most likely due to the SNS activity accompanying with food digestion (Ioannou, Chotard,</p><p>& Davila-Ross, 2015; van Baak, 2008). However, we also found that slow consumption of small amount foods (e.g. in-shell nuts) did not affect the nasal temperature of adult individuals (Natsuki, Mizuki, weighting about 60 kg); yet consumption of peanuts lowered the nasal temperature of a young chimpanzee (Hatsuka, weighting about 30 kg). We thus gave in-shell peanuts, sunflowers, and blocks of sugarcane to the adult chimpanzees and did not give any food to the young chimpanzee during a session in Experiment 2; the young chimpanzee nonetheless could stay on the chair and thus did not drop out from the test. In Experiment 1, consumption of small pieces of fruits (e.g. quarter-cut grapes) did not drop the nasal temperature of chimpanzees in WKPRC (all adults). </p><p>Self-directed scratching</p><p>Self-directed behaviors (SDB), such as scratching and auto-grooming, are widely used to measure anxiety level in chimpanzees in previous literatures. We did not take this measure in this study because it seemed that chimpanzees frequently exhibited scratching before/after food requests, and thus such reward-related conflict may be confounded with the stimulus-related stress. Figure S 1: Examples of stimuli in Experiment 1 (A) and Experiment 2 (B). Figure S 2: Examples of frames that were rated good or worse in quality. Figure S 3: The raw data before any data transformation in Experiment 1. </p><p>Figure S 4: The detrended data in Experiment 1 (before baseline corrected). </p><p>Figure S 5: The raw data before any data transformation in Experiment 2. In Figure S 6: The detrended data in Experiment 2 (before baseline corrected). The change in periorbital temperature</p><p>In humans, several studies have reported the increase in periorbital (the regions around eyes) temperature when people were startled by sudden noises (Naemura, Tsuda, & </p><p>Suzuki, 1993) and were telling a lie (Pavlidis, Levine, & Baukol, 2000). In this study, we thus preliminarily explored a possibility that emotional stimuli changed the periorbital temperature of chimpanzees. We measured the maximum temperature in periorbital regions (of both sides) every 10 second in Experiment 2. We did not, however, observe any significant changes in those regions (Figure S 7).</p><p>Figure S 7: The change in periorbital temperature (from the baseline) in the chimpanzees </p><p>(Experiment 2). Error bars denote ±95% confidence intervals, corrected for within-subject design. References in Supplemental Texts</p><p>Ioannou, S., Chotard, H., & Davila-Ross, M. (2015). No strings attached: physiological </p><p> monitoring of rhesus monkeys (Macaca mulatta) with thermal imaging. Frontiers in </p><p> behavioral neuroscience, 9, 160. doi: 10.3389/fnbeh.2015.00160</p><p>Naemura, A., Tsuda, K., & Suzuki, N. (1993). [Effects of loud noise on nasal skin </p><p> temperature]. Shinrigaku kenkyu: The Japanese journal of psychology, 64(1), 51-</p><p>54. </p><p>Pavlidis, I., Levine, J., & Baukol, P. (2000). Thermal imaging for anxiety detection. Paper </p><p> presented at the IEEE Workshop on Computer Vision Beyond the Visible </p><p>Spectrum: Methods and Applications, Hilton Head, SC. van Baak, M. A. (2008). Meal-induced activation of the sympathetic nervous system and </p><p> its cardiovascular and thermogenic effects in man. Physiology & Behavior, 94(2), </p><p>178-186. </p>