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Bitter taste perception is important in preventing animals from ingesting potentially toxic compounds. Whole-genome assembly (WGA) data have revealed that bitter taste receptor genes (TAS2Rs) comprise a multigene family with dozens of intact and disrupted genes in primates. However, publicly available WGA data is often incomplete, especially for multigene families. In this study, we employed a targeted capture (TC) approach specifically probing TAS2Rs for ten species of cercopithecid primates with diverse diet, including eight omnivorous cercopithecine species [three species of the genus Macaca (Macaca mulatta, Macaca fuscata, and Macaca nigra), two species of the genus Papio (Papio anubis and Papio hamadryas), three species of the tribe Cercopithecini (Erythrocebus patas, Chlorocebus sabaeus, and Cercopithecus mitis)] and two folivorous colobine species (Colobus polykomos and Semnopiethecus entellus). We designed RNA probes for all TAS2Rs that we modeled to be intact in the common ancestor of cercopithecids (“ancestral-cercopithecid TAS2R gene set”). The TC was followed by short-read and high-depth massive-parallel sequencing. TC retrieved more intact TAS2R genes than found in WGA databases. We confirmed a large number of gene “births” at the common ancestor of cercopithecids and found that the colobine common ancestor and the cercopithecine common ancestor had contrasting trajectories: four gene “deaths” and three gene births, respectively. The number of intact TAS2R genes was markedly reduced in colobines (25–28 detected via TC and 20–26 detected via WGA analysis) as compared with cercopithecines (27–36 via TC and 19–30 via WGA). Birth or death events occurred at almost every phylogenetic-tree branch, making the composition of intact genes variable among species. These results show that evolutionary change in intact TAS2R genes is a complex process, refute a simple general prediction that herbivory favours more TAS2R genes and have implications for understanding dietary adaptations and the evolution of detoxification abilities.

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Coat coloration represents one of the most diverse traits in primates, subject to selection due to its significant implications in camouflage, heat absorption, and communication. Melanism, a genetic trait leading to increased pigmentation and darker coloration, is particularly noteworthy. Among macaques, the black monkey (M. nigra ) exhibits a fully dark coat color, distinct from other species like M. ochreata, which display a brownish two-tone color pattern. To elucidate the genetic mechanism of melanism in M. nigra, we initially examined the hair root transcriptome in four individuals of both M. nigra and M. ochreata. We identified 350 genes with differentiated expression (DEGs) between the dark hair of M. nigra and M. ochreata. Notably, 263 DEGs were upregulated in M. nigra, significantly enriched in processes such as intermediate filament organization, skin epidermis development, trabecula formation, and T cell differentiation. Several DEGs enriched in pigmentation pathways were also upregulated, including CTLA4, FOXN1, GDPD3, KRT2, KRT27, LEF1, SLC40A1, and TYRP1. Of particular interest are LEF1 and TYRP1 for their roles in the Wnt signaling pathway and tyrosine metabolism, respectively. Furthermore, we identified a 9-bp deletion in the upstream of ASIP, which encodes a protein inhibiting melanin synthesis in M. nigra. However, the role of this deletion in melanism in M. nigra remains to be confirmed through additional functional assays. These findings will offer unique insights into the genetic basis of coat color variation in primates.

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コドモによる交尾妨害は、多くの霊長類で報告がなされているが、パタスモンキー（以下、パタス）ほど常習的な種はいない。飼育下パタスにおける先行研究によれば、コドモオスが交尾中のオスに向けて行うこと、28.6％では妨害の結果交尾が射精に至らないこと、しかし遊び顔で行うためハレムオスは極めて寛容であることが報告されている。そしてその機能として、コドモオスは、交尾妨害を通じてハレムオスの衰えを把握し群れの乗っ取りに繋げるという優位性テスト仮説が提唱されている。交尾季にあたる2023年8～9月に、ガーナ・モレ国立公園に生息するパタスMotel群を対象に交尾妨害のより妥当な機能仮説を探る目的で調査を行った。本群はオトナオス１頭、オトナメス4頭、コドモオス２頭、コドモメス4頭、アカンボウ雌雄各１頭からなる。本群の追跡34日349時間、うちアカンボウを除く全10頭の個体追跡は合計27日120時間であった。2歳半のオスDbは彼の個体追跡中2回の交尾妨害をしたが、その他のコドモ追跡中には、1度も妨害はなかった。アドリブも含め観察されたハレムオスの交尾13回中10回で妨害が起こり、妨害者はすべてDbであった。18回のマウンティング中10回で射精に至らず交尾不成功率は55.5%に達した。また、妨害を受けた10回の交尾のうち2回はその場で威嚇、5回は妨害者に向かって数歩走って前進する追い払いが生起したのだが、条件が良かった観察事例ではむしろ威嚇や追い払いをすることで、交尾が不成功になっており、遊び顔の信号がうまく機能していないためと考えられた。パタスは交尾期に群れ外オスが流入し、交尾妨害をしても劣位信号を発することでハレムオスから共存を許容されることが知られている。以上のことから、コドモオスによる交尾妨害は、将来オトナになった時に共存を許容される振る舞いを学習する機能があるという新たな仮説を提唱する。

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Bitter perception is mediated by G protein-coupled receptors TAS2Rs and plays an important role in avoiding toxins’ ingestion by inducing innate avoidance behavior in mammals. One of the best-studied TAS2Rs is TAS2R38, which mediates the perception of the bitterness of synthetic phenylthiocarbamide (PTC). In previous studies, we characterized the function of TAS2R38 in four allopatric species of Sulawesi macaques on Sulawesi Island from central to northern Sulawesi. We found variation in PTC taste perception both within and across species. In most cases, TAS2R38 was sensitive to PTC, with functional divergence among species. In the present study, we expand our samples to the south part of Sulawesi to determine whether this kind of divergence also exists in the South Sulawesi macaque species. We predict that some of the TAS2R38 in South Sulawesi macaques will have a different genetic background compared to the North Sulawesi macaques. We characterized the TAS2R38 of three Macaca species of Southern Sulawesi; M. maurus, M ochreata and M. brunnescens. We did experimental behavior on 12 individuals of M. maurus, 4 individuals of M. ochreata and 6 individuals of M. brunnescens, and found that 4 M. maura and 1 M. ochreata individuals cannot detect the bitterness of 2mM PTC, and thus called PTC-non-sensitive. Nucleotide sequence analysis revealed that the TAS2R38s are intact in all individuals of M.maurus and M. brunnescens. Three PTC non-sensitive individuals of M. maurus possessed TAS2R38 with intraspecific amino acid substitution at position 123 (R123C), while another individual possessed TAS2R38 with amino acid substitutions at positions 117, 130, and 134, which also exist in some individuals of M. tonkeana from central Sulawesi. We confirmed the PTC-non-sensitive of the TAS2R38 by functional assay. PTC non-sensitive individuals of M. ochreata lost two nucleotides at positions 505 and 506, resulting in a truncated protein. These results imply that there are also functional divergences of TAS2R38 in the southern species of Sulawesi macaques. Functional diversity of TAS2R38 might act as an adaptation to the local environment.

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Gut microbiome plays important role in animal nutrition by extracting energy and nutrients from other indigestible food. Previous studies have revealed diet as one of the key factors shaping gut microbiome composition and function. However, in contrast to the numerous lab-based studies on diet-gut microbiome dynamics, few studies investigate the causes and consequences of microbiota variation in wild. In wild, animals consume distinct diet throughout the year in response seasonal fluctuation in food distribution and abundance, hence gut microbiome composition and function may change accordingly. This study aims to investigate the seasonal variation in gut microbiome of wild Japanese macaques inhabiting Yakushima lowland. We directly examined the fermentative ability of gut microbiome by conducting in vitro digestibility monthly. Here we report the preliminary result regarding the seasonal variation in fermentative ability of macaques’ gut microbiome and discuss the relationship of gut microbiome function with seasonal dietary change.

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Grooming in primates is influenced by many variables, such as kinship, gender, age, dominance rank, level of affiliation, or reproductive status. One study suggests that higher-ranking males and females groom the opposite gender less frequently and shorter than lower-ranking males and females in Barbary macaques (M. sylvanus). In Japanese macaques (M. fuscata), however, higher-ranking males groomed estrous females longer than lower-ranking males, and male dominance rank showed no correlation with the duration of grooming they received from estrous females. The grooming between females and males cannot be explained by a single variable such as dominance rank or estrus. Subsequent studies have suggested that complex mechanisms may influence grooming patterns between females and males. I conducted an investigation of the effects of multiple variables which can affect mating partner choice on female and male grooming duration in Japanese macaques. I selected eight females of different (estimated) ages and dominance rank as focal animals from a single group (Miffy) of Japanese macaques living in western Yakushima. I followed the focal animals every other day from October 16 to December 28, 2024, and recorded copulation and grooming with males over the age of eight using continuous sampling method and focal sampling (Total focal sampling time: about 279 hours). Copulation occurrence, estrous status of females, dominance rank of females, age of females, dominance rank of males, age of males, affiliation of male (troop males vs non-troop males), and operational sex ratio (OSR, the number of estrous females per male) were analyzed as a variable that can influence preference of mating partner's choices. Copulation occurrence, estrus of females, age of females, affiliation of male, and OSR showed significant differences, but dominance rank of females, age of males, and dominance rank of males did not show significant differences in grooming duration between the opposite sexes grooming. Estrous females received longer grooming than non-estrous females, and non-troop males received longer grooming than troop males from females had copulated within 10 minutes. Among females had copulated within 10 minutes, older females received longer grooming than younger females from males. As OSR increased, estrous females had not copulated shorter and received less grooming from males. Some of the variables in this research showed an increasing grooming duration in accordance with variables preferred as mating partners in primates. I would like to suggest from this study that grooming between the opposite sexes may indicate preference as mating partners.

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