ヒトおよび現生大型類人猿の共通祖先の形質状態については，直接的証拠となる化石記録が不足していることもあり，議論は収束していない。個体発生のパターンは，遺伝的に決定される発生プログラムの修正を反映するので，形質の進化的起源を探るのに有用な情報である。四肢のプロポーションは運動様式と深く関わることが知られているが，ヒトおよび現生大型類人猿の四肢の相対成長を大規模に直接比較した研究はない。われわれは，X線CT装置を用いて，出生前後からオトナ期までのヒト，チンパンジー，ゴリラ，オランウータンの液浸・骨格標本を撮像し，得られた画像から骨幹の長さを上腕骨，橈骨，大腿骨，脛骨について測定した。データの分析には，直交回帰，ランダマイゼーション検定，及びQuick test（Tsutakawa and Hewett, 1977）を用いた。その結果，前肢長（上腕骨と橈骨骨幹長の和）と後肢長（大腿骨と脛骨骨幹長の和）はチンパンジーとオランウータンでは等成長を示したが，ヒトとゴリラでは後肢長の方が優位に成長しており，その程度はヒトの方が顕著であった。ヒトは大型類人猿に比べて前肢に対し後肢の成長が有意に大きいが，大型類人猿間では有意差はなかった。また，前肢長に対し後肢はヒト，チンパンジー，ゴリラ，オランウータンの順に長かった。現生大型類人猿では，基本的に出生前に前肢と後肢のプロポーションがほぼ決定するが，ヒトでは，出生後にも大きなプロポーション変化を示した。これは，効率的な二足歩行を可能にする極度に長い後肢を獲得するためと考えられた。また，ゴリラではわずかに後肢優位の成長を示すことから，これらのヒト上科において前肢と後肢のプロポーションを厳密に一定に保つような発生学的，あるいは機能的な制約は存在しないと考えられた。
2011年3月11日に起きた東日本大震災に伴い，東京電力福島第一原子力発電所（以下，原発）が爆発し，大量の放射性物質が放出された。われわれの研究グループでは，2012年度に原発から約70kmに位置する福島市に生息する野生二ホンザル（以下，福島サル）と約400kmに位置する青森県下北半島に生息する野生ニホンザル（以下，下北サル）の血液学的検査を行ったところ，福島サルの赤血球数・白血球数・ヘモグロビン濃度・ヘマトクリット値が，下北サルと比べて低値を示していたことを報告した（Ochiai et al. 2014）。本研究では，2012年度から2016年度の5年間に捕獲された福島サルを対象に，同様のモニタリングを行ったところ，引き続き汎血球減少傾向が見られた。その原因の検討のため骨髄の組織学的検査を行った。その結果，骨髄組織中に造血細胞が占める面積の割合は，下北サルと比較し福島サルでは低値を示し，また経年的に減少傾向を示したため，骨髄造血組織の減少によって末梢血球数が低下していることが示唆された。
We investigated the relatedness among adult females in wild Rhesus macaque (Macaca Mulatta) to understand what kinship affects social behavior. DNA were extracted from fecal samples and microsatellite markers were used for establishing kinship network. Totally 117 specimens of 38 individuals were used to perform molecular experiment, each individual was collected more than 2 specimens, each specimen was amplified over than 3 times. 6 high polymorphic microsatellite loci of 10 candidate loci were selected successfully. On average, the PIC value (Polymorphism information content) of microsatellite loci was 0.567, ranging from 0.467 to 0.744. Establishing kinship network and comparing it with affiliative behavior network, we found that significant correlation between kinship network and affiliative behavior network, which supported to kin selection theory. Supporting by hierarchy data, genetic similarity is useful to determine the pedigrees and to explain social behavior.
Limestone hills are an unusual habitat for primates, prompting them to evolve specific behavioral adaptations to the component karst habitat. From September 2012 to August 2013, we collected data on the diet of one group of Assamese macaques living in limestone forests at Nonggang National Nature Reserve, Guangxi Province, China, using instantaneous scan sampling. Assamese macaques were primarily folivorous, young leaves accounting for 75.5% and fruit accounted for only 20.1%. The young leaves of Bonia saxatilis, a shrubby, karstendemic bamboo that is superabundant in limestone hills, comprised the bulk of the average monthly diet. Moreover, macaques consumed significantly more bamboo leaves during the season when the availability of fruit declined, suggesting that bamboo leaves are an important fallback food for Assamese macaques in limestone forests. In addition, diet composition varied seasonally. The monkeys consumed significantly more fruit and fewer young leaves in the fruit - rich season than in the fruit - lean season. Fruit consumption was positively correlated with fruit availability, indicating that fruit is a preferred food for Assamese macaques. Of seventy - eight food species, only nine contributed >0.5% of the annual diet, and together these nine foods accounted for 90.7% of the annual diet. Our results suggest that bamboo consumption represents a key factor in the Assamese macaque's dietary adaptation to limestone habitat.
To what extent do primates - our closest phylogenetic relatives and thus the most relevant to understanding the origins of human hygiene practices - exhibit counterstrategies when faced with risk of infection? To address this, we conducted feeding-related infection-avoidance experiments with 5 species of Papionini and Hominini: Macaca fuscata fuscata, Macaca fascicularis, Mandrillus sphinx, Pan troglodytes troglodytes, and Pan paniscus. First, we found that free ranging Japanese macaques vary in their sensitivity to infection risk during foraging under both experimental and natural conditions, and the ‘hygienic tendencies’ of individuals were good predictors of their current levels of geohelminth infection. Then, we expanded our experimental protocol to include visual, olfactory and tactile cues of feces and other contaminants such as blood, semen, rotten meat and rotten fruit with captive chimpanzees, semi-free-ranging mandrills, group-housed long-tailed macaques and semi-free-ranging bonobos. Results indicate that subjects demonstrated risk-sensitivity to these potential contaminants, manifest as increased latencies to consumption of food rewards, maintenance of greater distances from contaminants, and/or outright refusals to consume food in test versus control conditions. Current work is testing whether risk-averse individuals with greater tendencies to avoid potential sources of contamination are less prone to infection and thus characterized by better general health than risk-prone individuals. These studies are aimed at better understanding behavioral immunity to infection among primates, which is fundamental to the understanding of the origins of human hygiene.
Castration has been used in nonhuman primates to control population demography, but the impact of this procedure on the social relationships of male Japanese macaques living in a complex society has not yet been investigated. This research examined fecal glucocorticoids (fGC) and fecal testosterone (fT) concentrations in male Japanese macaques residing in two social groups of contrasting environments (Jigokudani, Japan and Born Free Primate Sanctuary - BFS, Texas, USA), and males housed individually. The primary goal was to test the effect of castration on dominance hierarchy and steroid concentrations in Japanese macaques. We also investigated social, environmental and biological factors affecting steroid hormones. We collected behavioral data (focal animal and ad libitum sampling) to establish male dominance rank in the social groups, and fecal samples during the non-mating season from all males. We found that males housed in single cages had fT concentrations similar to castrated males and lower than intact social males. Castrated males maintained a dominance hierarchy primarily determined by age, and they were less aggressive than intact social males. Age had a positive relationship with fGC, but the opposite trend on fT levels. Rank and temperature were directly correlated to fT concentrations only in the intact social group. Our findings indicate that testosterone can be a consequence of the social structure of the group, and therefore is significantly affected by the social environment. Our results can contribute to the management and monitoring of primate populations in the wild and in captivity because they reveal that a complexity of connections link the social environment with male Japanese macaque steroid concentrations.
Food transfer is defined as the unresisted transfer of food from one food-motivated individual, the “possessor”, to another, the “recipient” (Feistner & McGrew 1989). This behavior has been described in different terms, including sharing, scrounging, and tolerbated theft, and it is usually accompanied by diverse behaviors such as begging, displacement of feeding spot, resistance of possessor, stealing, offering, and retrieving (Yamagiwa et al., 2015). Food transfer is mainly reported from apes, however, very few from genus macaca. Here we preliminary report food transfer behavior observed in stump-tailed macaques (Macaca arctoides) in Khao Krapuk Khao Taomor Non Hunting Area, Thailand. In this report, “Retrieving” - an individual takes food that another individual has dropped on the ground or placed there - is regarded as food transfer (see Yamagiwa et al., 2015). The aspect of transfer is different by the food item; transfer was more frequently occurred when they are eating food item that is not abundant and rare, or need to pay risk to obtain. Food transfer is often observed when monkeys are eating big food items which produce the food particles during eating. On the other hand, small food items or all-eatable food items are rarely transferred. Plant food transfer was observed not only among adults but also from adult to immature including transfer from mother to infant. Social interaction which can be interpreted as “Begging behavior” like presenting and greeting was also observed before food transfer occurred.