Rough and tumble play (RTP) is one of the most common types of social play in mammals. Yet, the functions of this activity are unclear. Panksepp’s (1998) study in rats (Rattus norvegicus) suggests that RTP might serve to cultivate self-regulation in animals laying the foundation for social morality. By investigating how chimpanzees regulate their aggression during RTP, we can have some insights into the origin of our moral conduct, namely behaving fairly. 124 hours of behavioral observation of six chimpanzees was conducted at Kyoto City Zoo. Continuous sampling was used to record the duration of RTP, types of play solicitation, the role of players, mode of termination, play intensity, and the presence or absence of play retrieve. Play bouts were categorized into three types based on how chimpanzees regulated aggression: fair, normal domination, and transgression. The findings of this study support the hypothesis that when a socially dominant chimpanzee plays with a subordinate partner, fair play will account for at least 30% of their total bouts. This result may shed new light on the study of animals’ social play by hinting at the existence of morality in chimpanzees which is likely to emerge in RTP. Also, the presence of play retrieve and direct play solicitation significantly extended the duration of play while play intensity did not. On this basis, the connection between social play and morality should be considered when conducting comparative studies on rough and tumble play in non-human animals.

Sulawesi macaques, seven endemic species in Sulawesi Island, Indonesia are optimal for studying the mechanism of genes shaping species differentiation. They have rapidly speciated from the common ancestor in a relatively short period and morphologically diversified. Exceptionally, they exhibited distinct dark coat color but with difference in color pattern between species. To clarify the genetic basis shaping specificity of species in Sulawesi macaques, we sequenced the exome of five species and screen out the differentiated SNPs. In total, we collected 46 saliva samples of five species in Sulawesi Island. After determined the exome sequence using human exome library, we computed the sites Fst (fixation index) value between each two neighboring species and filter the fixed SNPs as high differentiated sites. We found that hundreds of genes contained fixed SNPs between each pairwise neighboring species. These genes might be responsible to the species differentiation and evolve in directional selection on the traits. Further we investigated the pigmentation-related genes and confirmed the functional divergence of the genes in vitro. We found pigmentation-related genes were significantly enriched with fixed SNPs. We studied the cAMP induced ability of the melanocortin-1 receptor (MC1R), which regulates the synthesis and density of melanin production. The MC1R exhibited fixed amino acid sequence in each species and showed specific functional features in each species. These results demonstrate the genetic basis of the specificity species in Sulawesi macaques and the possibility of coat color divergence mechanism.

Mammals rely on the gut microbiome to process the indigestible plant materials. Through fermentation, the gut microbes transform fiber and the other indigestible materials into short-chain fatty acids and other nutrients, which are then absorbed by the host animals. For nonhuman primates and other animals that depend on plant material as the main component of their diet, the gut microbiome and its digestive function play a vital role in their feeding ecology. Although knowledge on the functions of the gut microbiome has increased greatly over the past few decades, our understanding of the mechanisms governing its ecology and evolution remains obscure. Comparing the gut microbiome of 19 populations of Japanese macaques Macaca fuscata across the Japanese archipelago, we assessed the relative roles of host genetic distance, geographic distance and dietary factors in influencing the macaque gut microbiome. Our results suggested that the macaques may maintain a core gut microbiome, while each population may have acquired some microbes from its specific habitat and diet. Diet-related factors such as season, forest and reliance on anthropogenic foods played a stronger role in shaping the macaque gut microbiome. Among closely related mammalian hosts, host genetics may have limited effects on the gut microbiome since the hosts generally have smaller physiological differences.

Given the close link between host physiology and gut microbiome, an improved understanding of the macaque gut microbiome may advance our knowledge in the ecological flexibility of Japanese macaques and the role of the gut microbiome in mammalian feeding ecology.