The diet and feeding behavior of the black-and-white colobus (Colobus guereza) in the Kalinzu Forest, Uganda

Development of an assessment method for freely moving nonhuman primates' eating behavior using manual and deep learning analysis

Purpose

Although eating is imperative for survival, few comprehensive methods have been developed to assess freely moving nonhuman primates' eating behavior. In the current study, we distinguished eating behavior into appetitive and consummatory phases and developed nine indices to study them using manual and deep learning-based (DeepLabCut) techniques.

Method

The indices were utilized to three rhesus macaques by different palatability and hunger levels to validate their utility. To execute the experiment, we designed the eating behavior cage and manufactured the artificial food. The total number of trials was 3, with 1 trial conducted using natural food and 2 trials using artificial food.

Result

As a result, the indices of highest utility for hunger effect were approach frequency and consummatory duration. Appetitive composite score and consummatory duration showed the highest utility for palatability effect. To elucidate the effects of hunger and palatability, we developed 2D visualization plots based on manual indices. These 2D visualization methods could intuitively depict the palatability perception and hunger internal state. Furthermore, the developed deep learning-based analysis proved accurate and comparable with manual analysis. When comparing the time required for analysis, deep learning-based analysis was 24-times faster than manual analysis. Moreover, temporal and spatial dynamics were visualized via manual and deep learning-based analysis. Based on temporal dynamics analysis, the patterns were classified into four categories: early decline, steady decline, mid-peak with early incline, and late decline. Heatmap of spatial dynamics and trajectory-related visualization could elucidate a consumption posture and a higher spatial occupancy of food zone in hunger and with palatable food.

Discussion

Collectively, this study describes a newly developed and validated multi-phase method for assessing freely moving nonhuman primate eating behavior using manual and deep learning-based analyses. These effective tools will prove valuable in food reward (palatability effect) and homeostasis (hunger effect) research.

Seasonal variations in the gut microbiota of white-headed black langur (Trachypithecus leucocephalus) in a limestone forest in Southwest Guangxi, China

Investigating gut microbiota is important for understanding the physiological adaptation of animals to food availability changes in fragmented habitats and consequently providing new ideas for the conservation of endangered wild animals. In this study, we explored the gut microbiota of the endangered white-headed black langur (Trachypithecus leucocephalus), which is endemic to the limestone forests of Southwest Guangxi, China, to understand its adaptation strategies to seasonal changes in habitat using 16S rRNA sequencing. Our results revealed significant seasonal variations in the gut microbiota of white-headed black langurs. In particular, the alpha diversity was higher in the rainy season than in the dry season, and the beta diversity was significantly different between the two seasons. At the phylum level, the relative abundance of Firmicutes, Actinobacteriota, and Proteobacteria was higher in the dry season than that in the rainy season, whereas that of Bacteroidetes, Spirochaetota, and Cyanobacteria was significantly higher in the rainy season than that in the dry season. At the family level, Oscillospiraceae and Eggerthellaceae were more abundant in the dry season than in the rainy season, whereas Lachnospiraceae, Ruminococcaceae, and Monoglobaceae were more abundant in the rainy season than in the dry season. These results could have been obtained due to seasonal changes in the diet of langurs in response to food plant phenology. In addition, the neutral community model revealed that the gut microbiota assembly of these langurs was dominated by deterministic processes and was more significantly affected by ecological factors in the dry season than in the rainy season, which could be linked to the higher dependence of these langurs on mature leaves in the dry season. We concluded that the seasonal variations in the gut microbiota of white-headed black langurs occurred in response to food plant phenology in their habitat, highlighting the importance of microbiota in responding to fluctuating ecological factors and adapting to seasonal dietary changes.

Dietary Choices of a Foregut-Fermenting Primate, Colobus guereza: A Comprehensive Approach Including Leaf Chemical and Mechanical Properties, Digestibility and Abundance

Free-ranging animals make dietary choices that affect their nutritional status and, ultimately, their health and fitness. We investigated food selection by a leaf-eating foregut-fermenting primate, the guereza (Colobus guereza), using multiple criteria, including chemical and mechanical properties, in vitro digestibility and leaf abundance, on the basis of 30 consecutive months of behavioral observations (4308 h in total) of a family group in the Kalinzu Forest, Uganda, as well as vegetation surveys. We noted that leaf toughness may be a proximate cue for the chemical properties of plant foods, especially for protein, which is an important selection factor used by primates. We also found that the in vitro digestibility of plant foods was greatly influenced by the concentrations of fiber and secondary compounds. At a broad level, none of the studied factors, including leaf chemical and mechanical properties, digestibility and abundance, affected whether guerezas consumed specific leaf items. At a more detailed level, however, protein content, digestibility and toughness were related to the percentage of foraging effort that guerezas devoted to specific items in our study site.

Specialised digestive adaptations within the hindgut of a colobine monkey

In mammal herbivores, fiber digestion usually occurs predominantly in either the foregut or the hindgut. Reports of mechanisms showing synergistic function in both gut regions for the digestion of fiber and other nutrients in wild mammals are rare because it requires integrative study of anatomy, physiology, and gut microbiome. Colobine monkeys (Colobinae) are folivorous, with high-fiber foods fermented primarily in their foreguts. A few colobine species live in temperate regions, so obtaining energy from fiber during the winter is essential. However, the mechanisms enabling this remain largely unknown. We hypothesized that such species possess specialized mechanisms to enhance fiber digestion in the hindgut and studied microbial and morphological digestive adaptations of golden snub-nosed monkeys (GSMs), Rhinopithecus roxellana. which is a temperate forest colobine from central China that experiences high-thermal-energy demands while restricted to a fibrous, low-energy winter diet. We tested for synergistic foregut and hindgut fiber digestion using comparisons of morphology, microbiome composition and function, and digestive efficiency. We found that the GSM colon has a significantly greater volume than that of other foregut-fermenting colobines. The microbiomes of the foregut and hindgut differed significantly in composition and abundance. However, while digestive efficiency and the expression of microbial gene functions for fiber digestion were higher in the foregut than in the hindgut, both gut regions were dominated by microbial taxa producing enzymes to enable active digestion of complex carbohydrates. Our data suggest that both the GSM foregut and hindgut facilitate fiber digestion and that an enlarged colon is likely an adaptation to accommodate high throughput of fiber-rich food during winter.

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How folivores extract adequate nutrition from their ultra-high-fiber diets remains unclear

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We studied the morphology, microbiome and digestive efficiency of gut for R. roxellana (GSM)

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Both fore- and hind-gut regions of GSM play important function of digesting complex carbohydrates

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An enlarged colon of GSM likely accommodates a high throughput of fiber-rich food during winter