Dietary diversity of an ecological and macronutritional generalist primate in a harsh high‐latitude habitat, the Taihangshan macaque ( Macaca mulatta tcheliensis )

DNA metabarcoding reveals the seasonal variation of dietary composition of Taihangshan macaque (Macaca mulatta tcheliensis), Jiyuan, north China

Dietary analysis in wildlife is fundamental for understanding their flexible response to seasonal changes and developing effective conservation management measures. Taihangshan macaque (Macaca mulatta tcheliensis) is the northernmost population of rhesus macaque, currently only distributed in the southern Mt. Taihangshan area. This area belongs to a semi-arid region resulting in limited plant food availability for Taihangshan macaques, with seasonal variation. Herein, we used a chloroplast trnL DNA metabarcoding approach to identify the plant diet diversity and composition from 100 fecal samples of Taihangshan macaque in four seasons (spring, summer, autumn, and winter) from 2020 to 2021. The results revealed that (1) a total of 48 distinct families, 88 genera, and 52 species within the 105 food items that were consumed by Taihangshan macaques throughout the year; (2) the diversity of food items exhibited significant differences across the four seasons; (3) Rosaceae, Rhamnaceae, Fagaceae, and Poaceae are the preferential food items for Taihangshan macaques and have different relative abundances, fluctuating with seasonal variation. DNA metabarcoding can expand our understanding of the repertoire of food items consumed by Taihangshan macaques by detecting some consumed food items in this population that were not yet discovered using traditional methods. Therefore, the integrative results from traditional methods and DNA metabarcoding can provide a fundamental understanding of dietary composition to guide the conservation management of Taihangshan macaques.

Investigating the dietary niches of fossil Plio-Pleistocene European macaques: The case of Macaca majori Azzaroli, 1946 from Sardinia

The genus Macaca includes medium- to large-bodied monkeys and represents one of the most diverse primate genera, also having a very large geographic range. Nowadays, wild macaque populations are found in Asia and Africa, inhabiting a wide array of habitats. Fossil macaques were also present in Europe from the Late Miocene until the Late Pleistocene. Macaques are considered ecologically flexible monkeys that exhibit highly opportunistic dietary strategies, which may have been critical to their evolutionary success. Nevertheless, available ecological information regarding fossil European species is very sparse, limiting our knowledge of their evolutionary history in this geographic area. To further our understanding of fossil European macaque ecology, we investigated the dietary ecology of Macaca majori, an insular endemic species from Sardinia. In particular, we characterized the dental capabilities and potential dietary adaptations of M. majori through dental topographic and enamel thickness analyses of two M2s from the Early Pleistocene site of Capo Figari (1.8 Ma). We also assessed its diet through dental microwear texture analysis, while the microwear texture of M. majori was also compared with microwear textures from other European fossil macaques from mainland Europe. The dental topographic and enamel thickness analyses suggest that M. majori frequently consumes hard/mechanically challenging and/or abrasive foods. The results of the dental microwear analysis are consistent with this interpretation and further suggest that M. majori probably exhibited more durophagous dietary habits than mainland Plio-Pleistocene macaques. Overall, our results indicate that M. majori probably occupied a different dietary niche compared to its mainland fossil relatives, which suggests that they may have inhabited different paleoenvironments.

Genomic analysis of the rhesus macaque (Macaca mulatta) and the cynomolgus macaque (Macaca fascicularis) uncover polygenic signatures of reinforcement speciation

Speciation can involve phases of divergent adaptation in allopatry and ecological/reproductive character displacement in sympatry or parapatry. Reproductive character displacement can result as a means of preventing hybridization, a process known as reinforcement speciation. In this study, we use whole-genome sequencing (WGS) of two closely related primate species that have experienced introgression in their history, the rhesus (Macaca mulatta) and cynomolgus (M. fascicularis) macaques, to identify genes exhibiting reproductive character displacement and other patterns consistent with reinforcement speciation. Using windowed scans of various population genetic statistics to identify signatures of reinforcement, we find 184 candidate genes associated with a variety of functions, including an overrepresentation of multiple neurological functions and several genes involved in sexual development and gametogenesis. These results are consistent with a variety of genes acting in a reinforcement process between these species. We also find signatures of introgression of the Y-chromosome that confirm previous studies suggesting male-driven introgression of M. mulatta into M. fascicularis populations. This study uses WGS to find evidence of the process of reinforcement in primates that have medical and conservation relevance.

Nutrient balancing in a fruit-specialist primate, the black-and-white ruffed lemur (Varecia variegata)

Animals' foraging behavior and dietary choices are, in part, driven by their ultimate function: to meet nutritional demands. However, depending on their degree of dietary specialization and the availability and distribution of food resources in their environment, species may utilize different nutritional strategies. With shifting plant phenology, increasing unpredictability of fruiting, and declining food quality in response to anthropogenic climate change, existing nutritional constraints may become exacerbated. Such changes are especially concerning for Madagascar's endemic fruit specialists given the nutrient-limitation of the island's landscapes. In this study, we examined the nutritional strategy of one such fruit-specialist primate, the black-and-white ruffed lemur (Varecia variegata), over a 12-month period (January to December 2018) in Ranomafana National Park, Madagascar. We hypothesized that Varecia would balance nonprotein energy (NPE) to protein (AP) at a high ratio similar to other frugivorous primates, and that they would prioritize protein intake given their high degree of frugivory. We found that Varecia balance NPE:AP at a ratio of 11:1, higher than in any other primate studied to date; however, diets shifted such that nutrient balancing varied seasonally (12.6:1 abundant-9.6:1 lean). Varecia meet NRC suggested recommendations of 5-8% of calories from protein, despite having a diet mostly comprising fruits. However, seasonal shifts in NPE intakes result in significant energy shortfalls during fruit-lean seasons. Flowers provide an important source of NPE during these periods, with flower consumption best predicting lipid intake, suggesting this species' ability to shift resource use. Nevertheless, achieving adequate and balanced nutrient intakes may become precarious in the face of increasing unpredictability in plant phenology and other environmental stochasticities resulting from climate change.

Nutrient-Sensitive Reinforcement Learning in Monkeys

In reinforcement learning (RL), animals choose by assigning values to options and learn by updating these values from reward outcomes. This framework has been instrumental in identifying fundamental learning variables and their neuronal implementations. However, canonical RL models do not explain how reward values are constructed from biologically critical intrinsic reward components, such as nutrients. From an ecological perspective, animals should adapt their foraging choices in dynamic environments to acquire nutrients that are essential for survival. Here, to advance the biological and ecological validity of RL models, we investigated how (male) monkeys adapt their choices to obtain preferred nutrient rewards under varying reward probabilities. We found that the nutrient composition of rewards strongly influenced learning and choices. Preferences of the animals for specific nutrients (sugar, fat) affected how they adapted to changing reward probabilities; the history of recent rewards influenced choices of the monkeys more strongly if these rewards contained the their preferred nutrients (nutrient-specific reward history). The monkeys also chose preferred nutrients even when they were associated with lower reward probability. A nutrient-sensitive RL model captured these processes; it updated the values of individual sugar and fat components of expected rewards based on experience and integrated them into subjective values that explained the choices of the monkeys. Nutrient-specific reward prediction errors guided this value-updating process. Our results identify nutrients as important reward components that guide learning and choice by influencing the subjective value of choice options. Extending RL models with nutrient-value functions may enhance their biological validity and uncover nutrient-specific learning and decision variables.SIGNIFICANCE STATEMENT RL is an influential framework that formalizes how animals learn from experienced rewards. Although reward is a foundational concept in RL theory, canonical RL models cannot explain how learning depends on specific reward properties, such as nutrients. Intuitively, learning should be sensitive to the nutrient components of the reward to benefit health and survival. Here, we show that the nutrient (fat, sugar) composition of rewards affects how the monkeys choose and learn in an RL paradigm and that key learning variables including reward history and reward prediction error should be modified with nutrient-specific components to account for the choice behavior observed in the monkeys. By incorporating biologically critical nutrient rewards into the RL framework, our findings help advance the ecological validity of RL models.

Diverse diets and low-fiber, low-tannin foraging preferences: Foraging criteria of Tibetan macaques (Macaca thibetana) at low altitude in Huangshan

Nutrient composition and food availability determine food choices and foraging strategies of animals, while altitude and geographical location affect species distribution and food availability. Tibetan macaques (Macaca thibetana) have sophisticated foraging strategies as the largest species in Macaca. They are important in understanding the ecological evolution of the entire genus. However, the mechanism of food selection in Tibetan macaques at low altitudes remains unclear. In this study, we researched a wild Tibetan macaques group (Tianhu Mountain Group, 29 individuals) living in a low-altitude area around Mt. Huangshan, Anhui Province, China. We used instantaneous scan sampling to observe these macaques' foraging behavior from September 2020 to August 2021. We recorded the dietary composition and food availability, compared the nutrient content of staple food and non-food items, and analyzed the role of key nutrients in food selection. We found that Tibetan macaques forage on 111 plants belonging to 93 genera and 55 families. The food types included fruits (52.5%), mature leaves (17.0%), bamboo shoots (14.4%), young leaves (6.3%), flowers (4.5%), others (2.1%), stems (1.9%), and tender shoots (1.3%). Tibetan macaques forage for a maximum of 76 plant species during spring. However, dietary diversity was highest during summer (H' = 3.052). Monthly fruit consumption was positively correlated with food availability. Staple foods are lower in fiber, tannin, and water than non-foods. In addition, the time spent foraging for specific foods was negatively correlated with the fiber and tannin content of the food. The results showed that Tibetan macaques' foraging plant species and food types were diverse, and their foraging strategies varied seasonally. Our findings confirmed the effect of nutrients on food choice in Tibetan macaques. We highlighted the important role of fiber and tannin in their food choices and suggested that the foraging behavior of Tibetan macaques is highly flexible and adaptive.

Diet and feeding behavior of a group of high-altitude rhesus macaques: high adaptation to food shortages and seasonal fluctuations

Diet and feeding behavior data are crucial to a deep understanding of the behavioral response and adaptation of primates to a high-altitude environment. From August 2019 to June 2021, we collected data on the feeding behavior of a high-altitude rhesus macaque Macaca mulatta group from Yajiang County, Western Sichuan Plateau, which has an altitude of over 3,500 m. The results showed that feeding (33.0 ± 1.8%) and moving (28.3 ± 2.6%) were the dominant behavior of rhesus macaques. Macaques ate 193 food items, comprising 11 food categories from 90 species. Our study found that plant roots (30.9±30.1%) and young leaves (28.0±33.1%) were the main foods eaten by macaques. The preferred foods of rhesus macaques were young leaves, fruits and seeds, and the consumption of these items was positively correlated with its food availability. When the availability of preferred foods was low, macaques took plant roots, barks and fallen leaves as fallback foods. In particular, roots were a dominant food item in winter, and this way of feeding became a key survival strategy. Our results suggest that, facing the relative scarcity and strong seasonal fluctuations of food resources in high-altitude habitat, macaques adopt active foraging strategies, relying on a variety of food species and adjusting flexibly their food choices based on food availability, which may help to maximize the energy efficiency of high-altitude macaques.

The gut microbiota of gibbons across host genus and captive site in China

Gut microbiota influences nutrient metabolism and immunity of animal hosts. Better understanding of the composition and diversity of gut microbiota contributes to conservation and management of threatened animals both in situ and ex situ. In this study, we applied 16S rRNA gene amplicon sequencing to evaluate the composition and diversity of the fecal bacterial community of four gibbon genera (Family Hylobatidae) at four Chinese zoos. The results showed that the dominant bacterial phyla were Bacteroidetes, Firmicutes, and Proteobacteria and dominant families were Prevotellaceae (Bacteroidetes), Spirochaetaceae (Spirochaetes) and Ruminococcaceae (Firmicutes) in the gut of all gibbons. Both captive site and host genus had significant effects on the relative abundance of dominant bacteria and structure of gut bacterial community. We found that captive site and host genus did not solely impact gut bacterial diversity, but the interaction between them did. This study provides basic knowledge for gut microbiota of all four gibbon genera and contributes to management and conservation of captive gibbons.

Seasonal variation in the behavioural ecology of samango monkeys (Cercopithecus albogularis schwarzi) in a southern latitude montane environment

Samango monkeys (Cercopithecus albogularis schwarzi) in the Soutpansberg Mountains, South Africa, experience a highly seasonal climate, with relatively cold, dry winters. They must show behavioural flexibility to survive these difficult conditions near the southern limit of the species' distribution and maintain the minimum nutritional intake they require. Through environmental monitoring and behavioural observations of a habituated group of samango monkeys, we explored how they adapted to the highly seasonal climate they experienced in the mountains. Our results indicated that the monkeys varied their foraging behaviours to account for changes in climate and daylight availability. The samangos increased their food intake in colder months, specifically leaves, likely due to an increased need for calories during winter to maintain body temperature. Samango monkeys have anatomical and physiological adaptations for digesting leaves, and these are likely important in explaining their ability to adapt to the broad range of climatic conditions they experience.

Meat eating by nonhuman primates: A review and synthesis

Most nonhuman primates prey on vertebrates. Meat-eating, defined as ingestion of vertebrate tissue, occurs in 12 families, ≥39 genera, and ≥89 species. It is most common in capuchins (Cebus and Sapajus spp.), baboons (Papio spp.), bonobos (Pan paniscus), and chimpanzees (Pan troglodytes) and modestly common in blue monkeys (Cercopithecus mitis), callitrichids (Callithrix spp. and Saguinus spp.), and squirrel monkeys (Saimiri spp.). It is uncommon in other cercopithecines, rare in other haplorhines and in lemurs, and virtually absent in colobines. Birds are the prey class eaten by the most species (≥53), followed by reptiles (≥48), amphibians (≥38), mammals (≥35), and fish (≥7). Major hypotheses for the importance of meat eating are that it is (1) mainly an energy source, especially (1a) when plant-source foods (PSFs) with high energy return rates are scarce (energy shortfall hypothesis); (2) mainly a protein source; and (3) mainly a source of micronutrients scarce in PSFs. Meat eating bouts sometimes provide substantial energy and protein, and some chimpanzees gain substantial protein from meat monthly or annually. However, meat typically accounts for only small proportions of feeding time and of total energy and protein intake, and quantitative data are inconsistent with the energy shortfall hypothesis. PSFs and/or invertebrates are presumably the main protein sources, even for chimpanzees. Support is strongest for the micronutrient hypothesis. Most chimpanzees eat far less meat than recorded for hunter-gatherers, but the highest chimpanzee estimates approach the lowest for African hunter-gatherers. In fundamental contrast to the human predatory pattern, other primates only eat vertebrates much smaller than they are, tool-assisted predation is rare except in some capuchins and chimpanzees, and tool use in carcass processing is virtually absent. However, harvesting of small prey deserves more attention with reference to the archaeological and ethnographic record.

Nutritional Dimensions of Invasive Success

Despite mounting calls for predictive ecological approaches rooted in physiological performance currencies, the field of invasive species biology has lagged behind. For instance, successful invaders are often predicted to consume diverse foods, but the nutritional complexity of foods often leaves food-level analyses short of physiological mechanisms. The emerging field of nutritional geometry (NG) provides new theory and empirical tools to predict invasive potential based on fundamental and realized nutritional niches. We review recent advances and synthesize NG predictions about behavioral traits that favor invasive establishment, and evolutionary dynamics that promote invasive spread. We also provide practical advice for applying NG approaches, and discuss the power of nutrition to achieve a more predictive invasion biology that explicitly integrates physiological mechanisms.

Living near the limits: Effects of interannual variation in food availability on diet and reproduction in a temperate primate, the Taihangshan macaque (Macaca mulatta tcheliensis)

Nutrient intake of animals is influenced by an interplay of external and internal factors, such as food availability and reproductive state, respectively. We used the nutritional geometry framework to analyze individual-based data on energy and nutrient intake in relation to reproductive state in a population of rhesus macaques (Macaca mulatta tcheliensis), which live in a harsh high-latitude habitat, the Taihangshan mountains of China, and exhibit strong reproductive seasonality. We combined data over a 3-year period on food availability, diets, reproductive output, and components of maternal investment to understand how Taihangshan macaques respond to variation in food availability and nutrition in reproduction. Our results show there was high interannual variation in availability of an important staple source of fat and carbohydrates (nonprotein energy), seeds of oak (Quercus spp). Despite this variability in seed availability skewing the dietary macronutrient ratios considerably (from 12.96% to 30.12% dietary energy from protein), total metabolizable energy intake was maintained across years during pregnancy. Lactating females had higher mean daily energy intakes than pregnant females. As in pregnant females, energy intake was maintained constant across years, but only when seed availability enabled the contribution of available protein to energy intake to be maintained between 15.32% (2013) and 17.97% (2015). In 2014, when seeds were scarce, lactating females had a shortfall in energy intake compared with 2013 and 2015. This corresponded with a reduction in the number of females giving birth (11 out of 23), but there was no interannual difference in survival rates. Compared to 2013 and 2015, in 2014 females had greater weight loss (drew on body reserves), moved less, and spent more time nursing their offspring. We discuss implications of these results for range limitation in Taihangshan macaques.