Misato Hayashi

How does stone-tool use emerge? Introduction of stones and nuts to naïve chimpanzees in captivity

Nut-cracking behavior has been reported in several communities in West Africa but not in East and Central Africa. Furthermore, even within nut-cracking communities, there are individuals who do not acquire the skill. The present study aimed to clarify the cognitive capability required for nut-cracking behavior and the process through which the the nut-cracking behavior emerges. To examine emergence, we provided three naïve adult chimpanzees with a single opportunity to observe human models. A human tester demonstrated nut-cracking behavior using a pair of stones and then supplied stones and nuts to the chimpanzee subjects. Two out of three chimpanzees proceeded to hit a nut on an anvil stone using a hammer stone, one of whom succeeded in cracking open the nuts during the first test session. The third chimpanzee failed to crack open nuts. We used four variables (object, location, body part used, and action) to describe stone/nut manipulation in order to analyze further the patterns of object manipulation exhibited by the subjects. The analysis revealed that there were three main difficulties associated with nut-cracking behavior. (1) The chimpanzee who failed at the task never showed hitting action. (2) The chimpanzee who failed at the task manipulated nuts but rarely stones. (3) The combination of three objects was not commonly observed in the three chimpanzees. We also discuss our results with reference to the effect of enculturation in captivity and the social context of learning in the wild.

Dynamic In-Hand Movements in Adult and Young Juvenile Chimpanzees (Pan troglodytes)

Descriptions of manual function in nonhuman primates have largely focused on static precision and power grasping (as first defined by Napier,1956), while identification and description of dynamic manual function are rare and incomplete. Here, we describe several forms of in-hand movements used by chimpanzees (Pan troglodytes) when manipulating small objects. In-hand movements are defined as the movement of an object within one hand via manipulation of the digits. We presented adult and young juvenile chimpanzees (ages 5-29 years) with a task that required inserting small objects through correspondingly shaped cutouts in a transparent Plexiglas panel. While attempting to insert the objects through the cutouts, the subjects used at least two forms of in-hand movements to change their grip on the object for more precise alignment. We describe in detail the in-hand movements they used and the variability observed in form and execution among the subjects. In general, the adult subjects used in-hand movements more frequently and used a wider variety of forms than did the young juvenile subjects, suggesting that in-hand movements are in the process of fine-tuning around the age of 5 years in chimpanzees. The dexterity exhibited by the adults, however, shows that the neuromuscular and morphological requirements for relatively complex digital manipulation are present in the adult chimpanzee.

Cortisol analysis of hair of captive chimpanzees (Pan troglodytes).

In addition to behavioral evaluations, stress assessments are also important for measuring animal welfare. Assessments of long-term stress are particularly important given that prolonged stress can affect physical health and reproduction. The use of hair cortisol as a marker of long-term stress has been increasing, but there has not yet been any report on the use of such methods with chimpanzees. Therefore, the purpose of this study was to establish and validate a methodology for analyzing hair cortisol in captive chimpanzees. In the first experiment, hair was removed from the arms of nine chimpanzees living in the Kumamoto Sanctuary (KS) and the regrown hair was sampled 3 months later. Fecal samples were collected periodically during the hair-growth period. The results showed that hair cortisol level was positively correlated with the rate of receiving aggression. Although the correlation between hair and fecal cortisol levels was not significant, the individual with the highest hair cortisol concentration also had the highest fecal cortisol concentration. These results suggest that hair cortisol may reflect long-term stress in chimpanzees. In the second experiment, we investigated the physiological factors affecting hair cortisol concentrations. We cut hair from the arms, sides, and backs of 25 chimpanzees living at the KS and the Primate Research Institute. The results revealed that cortisol varied based on source body part and hair whiteness. Therefore, we recommend that hair should always be collected from the same body part and that white hair should be avoided as much as possible.

Assessing the effects of cognitive experiments on the welfare of captive chimpanzees (Pan troglodytes) by direct comparison of activity budget between wild and captive chimpanzees.

We investigated the effects of cognitive experiments by direct comparison of activity budgets between wild and captive chimpanzees. One goal of captive management is to ensure that the activity budgets of captive animals are as similar as possible to those of their wild counterparts. However, such similarity has rarely been achieved. We compared the activity budget among three groups of chimpanzees: wild chimpanzees in Bossou (Guinea, n = 10), and captive chimpanzees who participated in cognitive experiments (experimental chimpanzees, n = 6) or did not participate in the experiments (nonexperimental chimpanzees, n = 6) at the Primate Research Institute (Japan). The experimental chimpanzees voluntarily participated in computer‐controlled cognitive tasks and small pieces of fruits were provided as rewards. The data from captivity were obtained on the experimental days (weekdays) and nonexperimental days (weekends). In both study sites, we followed each chimpanzee from about 7 a.m. until the time when chimpanzees started to rest in the evening. The behaviors were recorded every 1 min. The results showed that on weekdays, feeding time and resting time of the experimental chimpanzees were almost the same as those of wild chimpanzees. However, for the nonexperimental chimpanzees, feeding time was significantly shorter and resting time was longer than those of the wild chimpanzees. In contrast, no difference was found in feeding time or resting time of the two groups of captive chimpanzees on weekends. The results suggested that the cognitive experiments worked as an efficient method for food‐based enrichment. Am. J. Primatol. 73:1231–1238, 2011.

Stacking of blocks by chimpanzees: developmental processes and physical understanding

The stacking-block task has been used to assess cognitive development in both humans and chimpanzees. The present study reports three aspects of stacking behavior in chimpanzees: spontaneous development, acquisition process following training, and physical understanding assessed through a cylindrical-block task. Over 3 years of longitudinal observation of block manipulation, one of three infant chimpanzees spontaneously started to stack up cubic blocks at the age of 2 years and 7 months. The other two infants began stacking up blocks at 3 years and 1 month, although only after the introduction of training by a human tester who rewarded stacking behavior. Cylindrical blocks were then introduced to assess physical understanding in object–object combinations in three infant (aged 3–4) and three adult chimpanzees. The flat surfaces of cylinders are suitable for stacking, while the rounded surface is not. Block manipulation was described using sequential codes and analyzed focusing on failure, cause, and solution in the task. Three of the six subjects (one infant and two adults) stacked up cylindrical blocks efficiently: frequently changing the cylinders’ orientation without contacting the round side to other blocks. Rich experience in stacking cubes may facilitate subjects’ stacking of novel, cylindrical shapes from the beginning. The other three subjects were less efficient in stacking cylinders and used variable strategies to achieve the goal. Nevertheless, they began to learn the effective way of stacking over the course of testing, after about 15 sessions (75 trials).

Streptococcus troglodytae sp. nov., from the chimpanzee oral cavity.

Six strains, TKU 25, TKU 28, TKU 30, TKU 31(T), TKU 33 and TKU 34, were isolated from the oral cavity of a chimpanzee (Pan troglodytes). Colonies of strains grown on Mitis-Salivarius agar were similar in morphology to that of Streptococcus mutans. The novel strains were Gram-stain-positive, facultatively anaerobic cocci that lacked catalase activity. Analysis of the partial 16S rRNA gene sequences of these isolates showed that the most closely related strain was the type strain of S. mutans (96.4 %). The next closely related strains to the isolates were the type strains of Streptococcus devriesei (94.5 %) and Streptococcus downei (93.9 %). These isolates could be distinguished from S. mutans by inulin fermentation and alkaline phosphatase activity (API ZYM system). The peptidoglycan type of the novel isolates was Glu-Lys-Ala(3). Strains were not susceptible to bacitracin. On the basis of phenotypic characterization, partial 16S rRNA gene and two housekeeping gene (groEL and sodA) sequence data, we propose a novel taxon, Streptococcus troglodytae sp. nov.; the type strain is TKU 31(T) ( = JCM 18038(T) = DSM 25324(T)).

Analysis of hair cortisol levels in captive chimpanzees: Effect of various methods on cortisol stability and variability

Graphical abstract Summary of the experimental process. The items colored blue affected the results of the hair cortisol analysis in the present study. The stippled items were found to affect the results obtained in our previous study [1].

Perspectives on object manipulation and action grammar for percussive actions in primates

The skill of object manipulation is a common feature of primates including humans, although there are species-typical patterns of manipulation. Object manipulation can be used as a comparative scale of cognitive development, focusing on its complexity. Nut cracking in chimpanzees has the highest hierarchical complexity of tool use reported in non-human primates. An analysis of the patterns of object manipulation in naive chimpanzees after nut-cracking demonstrations revealed the cause of difficulties in learning nut-cracking behaviour. Various types of behaviours exhibited within a nut-cracking context can be examined in terms of the application of problem-solving strategies, focusing on their basis in causal understanding or insightful intentionality. Captive chimpanzees also exhibit complex forms of combinatory manipulation, which is the precursor of tool use. A new notation system of object manipulation was invented to assess grammatical rules in manipulative actions. The notation system of action grammar enabled direct comparisons to be made between primates including humans in a variety of object-manipulation tasks, including percussive-tool use.

Impaired Air Conditioning within the Nasal Cavity in Flat-Faced Homo.

We are flat-faced hominins with an external nose that protrudes from the face. This feature was derived in the genus Homo, along with facial flattening and reorientation to form a high nasal cavity. The nasal passage conditions the inhaled air in terms of temperature and humidity to match the conditions required in the lung, and its anatomical variation is believed to be evolutionarily sensitive to the ambient atmospheric conditions of a given habitat. In this study, we used computational fluid dynamics (CFD) with three-dimensional topology models of the nasal passage under the same simulation conditions, to investigate air-conditioning performance in humans, chimpanzees, and macaques. The CFD simulation showed a horizontal straight flow of inhaled air in chimpanzees and macaques, contrasting with the upward and curved flow in humans. The inhaled air is conditioned poorly in humans compared with nonhuman primates. Virtual modifications to the human external nose topology, in which the nasal vestibule and valve are modified to resemble those of chimpanzees, change the airflow to be horizontal, but have little influence on the air-conditioning performance in humans. These findings suggest that morphological variation of the nasal passage topology was only weakly sensitive to the ambient atmosphere conditions; rather, the high nasal cavity in humans was formed simply by evolutionary facial reorganization in the divergence of Homo from the other hominin lineages, impairing the air-conditioning performance. Even though the inhaled air is not adjusted well within the nasal cavity in humans, it can be fully conditioned subsequently in the pharyngeal cavity, which is lengthened in the flat-faced Homo. Thus, the air-conditioning faculty in the nasal passages was probably impaired in early Homo members, although they have survived successfully under the fluctuating climate of the Plio-Pleistocene, and then they moved “Out of Africa” to explore the more severe climates of Eurasia.

Streptococcus panodentis sp. nov. from the oral cavities of chimpanzees

Three strains TKU9, TKU49 and TKU50T, were isolated from the oral cavities of chimpanzees (Pan troglodytes). The isolates were all gram‐positive, facultative anaerobic cocci that lacked catalase activity. Analysis of partial 16S rRNA gene sequences showed that the most closely related species was Streptococcus infantis (96.7%). The next most closely related species to the isolates were S. rubneri, S. mitis, S. peroris and S. australis (96.6 to 96.4%). Based on the rpoB and gyrB gene sequences, TKU50T was clustered with other member of the mitis group. Enzyme activity and sugar fermentation patterns differentiated this novel bacterium from other members of the mitis group streptococci. The DNA G + C content of strain TKU50T was 46.7 mol%, which is the highest reported value for members of the mitis group (40–46 mol%). On the basis of the phenotypic characterization, partial 16S rRNA gene and sequences data for two housekeeping gene (gyrB and rpoB), we propose a novel taxa, S. panodentis for TKU 50T (type strain = CM 30579T = DSM 29921T), for these newly described isolates.