Western chimpanzees (Pan troglodytes verus) access a nutritionally balanced, high energy, and abundant food, baobab (Adansonia digitata) fruit, with extractive foraging and reingestion

Intrinsic to several hypotheses explaining the evolution of foraging behavior complexity, such as proto-tool use, is the assumption that more complex ingestive behaviors are adaptations allowing individuals to access difficult to procure but nutritionally or energetically rewarding foods. However, nutritional approaches to understanding this complexity have been underutilized. The goal of this study was to evaluate potential nutritional determinants of two unusual foraging behaviors, fruit cracking with anvils and seed reingestion, by adult male western chimpanzees (Pan troglodytes verus) at Fongoli, Senegal during the baobab (Adansonia digitata) fruit season. We examined these behaviors in relation to nutrient and energy intake, and compared macronutrient and energy concentrations found in baobab fruits to other plant foods. Adult males ingested at least 31 distinct foods from 23 plant species. Baobab fruit comprised the majority of daily energy intake (68 ± 34%, range: 0%-98%). The energetic concentration of baobab fruit varied by phenophase and part ingested, with ripe and semi-ripe fruit ranking high in energy return rate. Males preferred ripe and semi-ripe baobab fruit but unripe fruit intake was higher overall. The seed kernels were high in protein and fat relative to fruit pulp, and these kernels were easier to access during the unripe stage. During the ripe stage, seed kernels were accessible by reingestion, after the seed coat was softened during gut passage. In addition to providing macronutrients and energy, baobab fruit was a relatively abundant food source. We conclude that baobab pulp and seed are high quality foods at Fongoli during the baobab season because they are nutritionally balanced, high in energy, and relatively abundant in the environment. These nutritional and abundance characteristics may explain, in part, why these chimpanzees use anvils and reingestion to access a mechanically challenging food.

Understanding the evolution of nutritive taste in animals: Insights from biological stoichiometry and nutritional geometry

A major conceptual gap in taste biology is the lack of a general framework for understanding the evolution of different taste modalities among animal species. We turn to two complementary nutritional frameworks, biological stoichiometry theory and nutritional geometry, to develop hypotheses for the evolution of different taste modalities in animals. We describe how the attractive tastes of Na-, Ca-, P-, N-, and C-containing compounds are consistent with principles of both frameworks based on their shared focus on nutritional imbalances and consumer homeostasis. Specifically, we suggest that the evolution of multiple nutritive taste modalities can be predicted by identifying individual elements that are typically more concentrated in the tissues of animals than plants. Additionally, we discuss how consumer homeostasis can inform our understanding of why some taste compounds (i.e., Na, Ca, and P salts) can be either attractive or aversive depending on concentration. We also discuss how these complementary frameworks can help to explain the evolutionary history of different taste modalities and improve our understanding of the mechanisms that lead to loss of taste capabilities in some animal lineages. The ideas presented here will stimulate research that bridges the fields of evolutionary biology, sensory biology, and ecology.

Life-history theory provides a framework for detecting resource limitation: a test of the Nutritional Buffer Hypothesis

For ungulates and other long-lived species, life-history theory predicts that nutritional reserves are allocated to reproduction in a state-dependent manner because survival is highly conserved. Further, as per capita food abundance and nutritional reserves decline (i.e., density dependence intensifies), reproduction and recruitment become increasingly sensitive to weather. Thus, the degree to which weather influences vital rates should be associated with proximity to nutritional carrying capacity-a notion that we refer to as the Nutritional Buffer Hypothesis. We tested the Nutritional Buffer Hypothesis using six moose (Alces alces) populations that varied in calf recruitment (33-69 calves/100 cows). We predicted that populations with high calf recruitment were nutritionally buffered against the effects of unfavorable weather, and thus were below nutritional carrying capacity. We applied a suite of tools to quantify habitat and nutritional condition of each population and found that increased browse condition, forage quality, and body fat were associated with increased pregnancy and calf recruitment, thereby providing multiple lines of evidence that declines in calf recruitment were underpinned by resource limitation. From 2001 to 2015, recruitment was more sensitive to interannual variation in weather (e.g., winter severity, drought) and plant phenology (e.g., duration of spring) for populations with reduced browse condition, forage quality, and body fat, suggesting these populations lacked the nutritional reserves necessary to buffer demographic performance against the effects of unfavorable weather. Further, average within-population calf recruitment was determined by regional climatic variation, suggesting that the pattern of reduced recruitment near the southern range boundary of moose stems from an interaction between climate and resource limitation. When coupled with information on habitat, nutrition, weather, and climate, life-history theory provides a framework to estimate nutritional limitation, proximity to nutritional carrying capacity, and impacts of climate change for ungulates.

Integrating omics to characterize eco-physiological adaptations: How moose diet and metabolism differ across biogeographic zones

With accelerated land conversion and global heating at northern latitudes, it becomes crucial to understand, how life histories of animals in extreme environments adapt to these changes. Animals may either adapt by adjusting foraging behavior or through physiological responses, including adjusting their energy metabolism or both. Until now, it has been difficult to study such adaptations in free-ranging animals due to methodological constraints that prevent extensive spatiotemporal coverage of ecological and physiological data.Through a novel approach of combining DNA-metabarcoding and nuclear magnetic resonance (NMR)-based metabolomics, we aim to elucidate the links between diets and metabolism in Scandinavian moose Alces alces over three biogeographic zones using a unique dataset of 265 marked individuals.Based on 17 diet items, we identified four different classes of diet types that match browse species availability in respective ecoregions in northern Sweden. Individuals in the boreal zone consumed predominantly pine and had the least diverse diets, while individuals with highest diet diversity occurred in the coastal areas. Males exhibited lower average diet diversity than females.We identified several molecular markers indicating metabolic constraints linked to diet constraints in terms of food availability during winter. While animals consuming pine had higher lipid, phospocholine, and glycerophosphocholine concentrations in their serum than other diet types, birch- and willow/aspen-rich diets exhibit elevated concentrations of several amino acids. The individuals with highest diet diversity had increased levels of ketone bodies, indicating extensive periods of starvation for these individuals.Our results show how the adaptive capacity of moose at the eco-physiological level varies over a large eco-geographic scale and how it responds to land use pressures. In light of extensive ongoing climate and land use changes, these findings pave the way for future scenario building for animal adaptive capacity.

Selective Fatty Acid Retention and Turnover in the Freshwater Amphipod Pallaseopsis quadrispinosa

Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1ω7 and partly 18:1ω9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, α-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain ω-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.

Condensed tannins in the diet of folivorous diademed sifakas and the gap between crude and available protein

Tannins, a type of plant secondary metabolite, are well-known for their ability to precipitate proteins and thereby reduce the protein available to consumers. Most primate studies have focused on condensed tannins (CTs) as they were thought to be the most effective type of tannin at preventing protein acquisition, but there is growing recognition that other types of tannins can bind to proteins, suggesting the division among tannin types is not as clear-cut as previously thought. Although previous studies have documented the presence of CTs in primate diets and primates' behavioral responses to them, our understanding of tannins remains limited because few researchers have used Sephadex column purification to accurately determine tannin concentrations, and few have used in vitro assays to determine available protein content and the tannins' effectiveness in binding protein. In this study, we documented diademed sifaka (Propithecus diadema) diet from June to August 2018 at Tsinjoarivo, Madagascar (in two forests with varying degrees of habitat disturbance) and quantified CT concentration and actual available protein in foods. Eleven of the fourteen top foods tested contained CTs (concentrations: 4.8%-39.3% dry matter). An in vitro assay showed available protein was strikingly low in six of the eleven top foods (e.g., little to no apparent available protein, despite high crude protein). Overall, our findings suggest sifakas acquire less protein than previously recognized and probably have adaptations to counteract tannins. Such studies of available protein are critical in understanding dietary constraints on sifaka populations and the evolution of their diet choice strategies; despite the conventional wisdom that leaves are protein-rich, folivorous primates may indeed be protein-limited. However, further studies are necessary to determine if sifakas have counter-adaptations to tannins, and if they absorb more protein than our analyses suggest, perhaps receiving protein that we were unable to detect with the current techniques (e.g., pollen).

The complexity of co-limitation: nutrigenomics reveal non-additive interactions of calcium and phosphorus on gene expression in Daphnia pulex

Many lakes across Canada and northern Europe have experienced declines in ambient phosphorus (P) and calcium (Ca) supply for over 20 years. While these declines might create or exacerbate nutrient limitation in aquatic food webs, our ability to detect and quantify different types of nutrient stress on zooplankton remains rudimentary. Here, we used growth bioassay experiments and whole transcriptome RNAseq, collectively nutrigenomics, to examine the nutritional phenotypes produced by low supplies of P and Ca separately and together in the freshwater zooplankter Daphnia pulex. We found that daphniids in all three nutrient-deficient categories grew slower and differed in their elemental composition. Our RNAseq results show distinct responses in singly limited treatments (Ca or P) and largely a mix of these responses in animals under low Ca and P conditions. Deeper investigation of effect magnitude and gene functional annotations reveals this patchwork of responses to cumulatively represent a co-limited nutritional phenotype. Linear discriminant analysis identified a significant separation between nutritional treatments based upon gene expression patterns with the expression patterns of just five genes needed to predict animal nutritional status with 99% accuracy. These data reveal how nutritional phenotypes are altered by individual and co-limitation of two highly important nutritional elements (Ca and P) and provide evidence that aquatic consumers can respond to limitation by more than one nutrient at a time by differentially altering their metabolism. This use of nutrigenomics demonstrates its potential to address many of the inherent complexities in studying interactions between multiple nutritional stressors in ecology and beyond.

Plant carbohydrate content limits performance and lipid accumulation of an outbreaking herbivore

Locusts are major intermittent threats to food security and the ecological factors determining where and when these occur remain poorly understood. For many herbivores, obtaining adequate protein from plants is a key challenge. We tested how the dietary protein : non-structural carbohydrate ratio (p : c) affects the developmental and physiological performance of 4th-5th instar nymphs of the South American locust, Schistocerca cancellata, which has recently resurged in Argentina, Bolivia and Paraguay. Field marching locusts preferred to feed on high carbohydrate foods. Field-collected juveniles transferred to the laboratory selected artificial diets or local plants with low p : c. On single artificial diets, survival rate increased as foods became more carbohydrate-biased. On single local plants, growth only occurred on the plant with the lowest p : c. Most local plants had p : c ratios substantially higher than optimal, demonstrating that field marching locusts must search for adequate carbohydrate or their survival and growth will be carbohydrate-limited. Total body lipids increased as dietary p : c decreased on both artificial and plant diets, and the low lipid contents of field-collected nymphs suggest that obtaining adequate carbohydrate may pose a strong limitation on migration for S. cancellata. Anthropogenic influences such as conversions of forests to pastures, may increase carbohydrate availability and promote outbreaks and migration of some locusts.

Investigating Plant Micro-Remains Embedded in Dental Calculus of the Phoenician Inhabitants of Motya (Sicily, Italy)

Plant records reveal remarkable evidence about past environments and human cultures. Exploiting dental calculus analysis and using a combined approach of microscopy and gas chromatography mass spectrometry, our research outlines dietary ecology and phytomedicinal practices of the ancient community of Motya (Sicily, eight to sixth century BC), one of the most important Phoenician settlements in the Mediterranean basin. Micro-remains suggest use or consumption of Triticeae cereals, and animal-derived sources (e.g., milk and aquatic birds). Markers of grape (or wine), herbs, and rhizomes, endemic of Mediterranean latitudes and the East, provide insight into the subsistence of this colony, in terms of foodstuffs and phytotherapeutic products. The application of resins and wood of Gymnosperms for social and cultural purposes is hypothesized through the identification of Pinaceae secondary metabolites and pollen grains. The information hidden in dental calculus discloses the strong human-plant interaction in Motya’s Phoenician community, in terms of cultural traditions and land use.

Temperature dependency of predation: Increased killing rates and prey mass consumption by predators with warming

Temperature dependency of consumer-resource interactions is fundamentally important for understanding and predicting the responses of food webs to climate change. Previous studies have shown temperature-driven shifts in herbivore consumption rates and resource preference, but these effects remain poorly understood for predatory arthropods. Here, we investigate how predator killing rates, prey mass consumption, and macronutrient intake respond to increased temperatures using a laboratory and a field reciprocal transplant experiment. Ectothermic predators, wolf spiders (Pardosa sp.), in the lab experiment, were exposed to increased temperatures and different prey macronutrient content (high lipid/low protein and low lipid/high protein) to assess changes in their killing rates and nutritional demands. Additionally, we investigate prey mass and lipid consumption by spiders under contrasting temperatures, along an elevation gradient. We used a field reciprocal transplant experiment between low (420 masl; 26°C) and high (2,100 masl; 15°C) elevations in the Ecuadorian Andes, using wild populations of two common orb-weaver spider species (Leucauge sp. and Cyclosa sp.) present along the elevation gradient. We found that killing rates of wolf spiders increased with warmer temperatures but were not significantly affected by prey macronutrient content, although spiders consumed significantly more lipids from lipid-rich prey. The field reciprocal transplant experiment showed no consistent predator responses to changes in temperature along the elevational gradient. Transplanting Cyclosa sp. spiders to low- or high-elevation sites did not affect their prey mass or lipid consumption rate, whereas Leucauge sp. individuals increased prey mass consumption when transplanted from the high to the low warm elevation. Our findings show that increases in temperature intensify predator killing rates, prey consumption, and lipid intake, but the responses to temperature vary between species, which may be a result of species-specific differences in their hunting behavior and sensitivity to temperature.

Sexual Dimorphism in the Multielemental Stoichiometric Phenotypes and Stoichiometric Niches of Spiders

Nutritional limitations may shape populations and communities of organisms. This phenomenon is often studied by treating populations and communities as pools of homogenous individuals with average nutritional optima and experiencing average constraints and trade-offs that influence their fitness in a standardized way. However, populations and communities consist of individuals belonging to different sexes, each with specific nutritional demands and limitations. Taking this into account, we used the ecological stoichiometry framework to study sexual differences in the stoichiometric phenotypes, reflecting stoichiometric niches, of four spider taxa differing in the hunting mode. The species and sexes differed fundamentally in their elemental phenotypes, including elements beyond those most commonly studied (C, N and P). Both species and sexes were distinguished by the C:N ratio and concentrations of Cu, K and Zn. Species additionally differed in concentrations of Na, Mg and Mn. Phosphorous was not involved in this differentiation. Sexual dimorphism in spiders' elemental phenotypes, related to differences in their stoichiometric niches, suggests different nutritional optima and differences in nutritional limitation experienced by different sexes and species. This may influence the structure and functioning of spider populations and communities.

Botanical Composition and Diet Quality of the Vicuñas (Vicugna vicugna Mol.) in Highland Range of Parinacota, Chile

Simple Summary

For the proper management of grazing wild ungulates, it is very important to know the botanical composition and quality of their selected diets. In the case of the vicuña, a wild camelid that lives in the Chilean highlands, there is little information related to these aspects. Therefore, in this work, the variations in the botanical composition and quality of their diets throughout the year were studied, which were estimated by analyzing the plant fragments found in the feces and the concentration of nitrogen within them. The vicuña mainly selects grasses from dry and wet grassland but is also capable of selecting other species, such as graminoids and dicotyledonous herbs. These plants contribute to obtaining a diverse and high-quality diet, this being an efficient foraging strategy to be able to consume a good quality diet, mainly in the months of high nutritional demand, which coincides with the summer rainy season.

Abstract

Understanding the botanical composition of herbivores’ diets and their nutritional quality is an important question in the development of sustainable strategies for the management of natural resources. In Chilean highland vicuña-grazed grasslands, there is little information in this regard and, therefore, this study aimed to determine the year-round profile of the diet’s botanical composition and quality. In highland grasslands, on an area of 21.9 ha, continuously grazed for 3.06 VU/ha/year (18°03′ S, 69°13′ W; 4425 m.o.s.l), twelve feces piles were sampled monthly and were analyzed through microhistology, and the nitrogen concentration [NF, OM basis] was determined. The botanical composition, diversity (J) and selectivity index (E_i) of the main species were estimated. Diets were composed of dry–grassland grasses (37.7%), wet–grassland grasses (36.6%), graminoids (14.3%) and forbs (10.2%). The diet diversity ranged from 0.79 (dry–winter) to 0.87 (wet–summer). The main dominant grassland species obtained negative E_i values. The annual mean value of [NF] was estimated as 1.82%, with a higher value in summer months (2.21%), which coincides with the physiological states of higher nutritional demand. The vicuñas behave like generalist ungulates, having a high degree of selectivity towards grass species, which mostly fulfill a nutritional role in subsistence and a functional role in survival, applying foraging strategies that allow them to obtain a better quality diet during the season of greatest nutritional demand.

Growth and survival of the superorganism: Ant colony macronutrient intake and investment

In this study, we used two common ant species (Lasius niger and Lasius neoniger) to assay how they translate variation in the diet (both in composition and frequency) into growth. We measured colony development for over 8 months and measured several phenotypic traits of the worker caste, and examined whether forager preference corresponded with diet quality. Optimal colony growth was a balance between survival and growth, and each of these was maximized with different nutrient regimes. Interestingly, forager preference was not totally aligned with the diet that maximized colony growth. Our results highlight that: (a) organism and superorganism size are controlled by the same nutrients, and this may reflect a common molecular basis for size across life's organizational levels, (b) there are nutrient trade-offs that are associated with life-history trade-offs, likely leading to selection for a balanced diet, and (c) the connection between the preference of foragers for different nutrients and how nutrient combinations affect colony success and demographics are complex and only beginning to be understood.

Feeding preferences and nutritional niche of wild water buffalo (Bubalus arnee) in Koshi Tappu Wildlife Reserve, Nepal

The nutritional characteristics of food resources play an important role in the foraging behavior of animals and can provide information valuable to their conservation and management. We examined the nutritional ecology of wild water buffalo (Bubalus arnee; hereafter "buffalo") in the Koshi Tappu Wildlife Reserve of Nepal during autumn using a multidimensional nutritional niche framework. We identified 54 plant species as being foraged by buffalo. We found that buffalo consumed graminoids and forbs 2-3 times more frequently than browse items. Proximate analyses of the 16 most frequently foraged plants indicated that buffalo diets were highest in carbohydrate (40.41% ± 1.82%) followed by crude protein (10.52% ± 0.93%) and crude fat (1.68% ± 0.23%). The estimated macronutrient balance (i.e., realized nutrient niche) of the buffalo diet (20.5% protein: 72.8% carbohydrate: 6.7% lipid) was not significantly different than the average balance of all analyzed food items based on 95% confidence regions. Our study suggests that buffalo are likely macronutrient specialists, yet may be generalists in the sense that they feed on a wide range of food items to achieve a nutrient balance similar to that available in forage items. However, the four most frequently consumed items tended to be higher in protein energy than less frequently consumed foods, suggesting some preference for higher protein forage relative to relatively abundant carbohydrates. Although limited in scope, our study provides important information on the nutritional ecology of buffalo, which may be useful for the conservation and management of this endangered species.

Herbivory meets fungivory: insect herbivores feed on plant pathogenic fungi for their own benefit

Plants are regularly colonised by fungi and bacteria, but plant-inhabiting microbes are rarely considered in studies on plant-herbivore interactions. Here we show that young gypsy moth (Lymantria dispar) caterpillars prefer to feed on black poplar (Populus nigra) foliage infected by the rust fungus Melampsora larici-populina instead of uninfected control foliage, and selectively consume fungal spores. This consumption, also observed in a related lepidopteran species, is stimulated by the sugar alcohol mannitol, found in much higher concentration in fungal tissue and infected leaves than uninfected plant foliage. Gypsy moth larvae developed more rapidly on rust-infected leaves, which cannot be attributed to mannitol but rather to greater levels of total nitrogen, essential amino acids and B vitamins in fungal tissue and fungus-infected leaves. Herbivore consumption of fungi and other microbes may be much more widespread than commonly believed with important consequences for the ecology and evolution of plant-herbivore interactions.

Open Data for Open Questions in Comparative Nutrition

Achieving a better understanding of the consequences of nutrition to animal fitness and human health is a major challenge of our century. Nutritional ecology studies increasingly use nutritional landscapes to map the complex interacting effects of nutrient intake on animal performances, in a wide range of species and ecological contexts. Here, we argue that opening access to these hard-to-obtain, yet considerably insightful, data is fundamental to develop a comparative framework for nutrition research and offer new quantitative means to address open questions about the ecology and evolution of nutritional processes.

Diet composition and social environment determine food consumption, phenotype and fecundity in an omnivorous insect

Nutrition is the single most important factor for individual's growth and reproduction. Consequently, the inability to reach the nutritional optimum imposes severe consequences for animal fitness. Yet, under natural conditions, organisms may face a mixture of stressors that can modulate the effects of nutritional asymmetry. For instance, stressful environments caused by intense interaction with conspecifics. Here, we subjected the house cricket Acheta domesticus to (i) either of two types of diet that have proved to affect cricket performance and (ii) simultaneously manipulated their social environment throughout their complete life cycle. We aimed to track sex-specific consequences for multiple traits during insect development throughout all life stages. Both factors affected critical life-history traits with potential population-level consequences: diet composition induced strong effects on insect development time, lifespan and fitness, while the social environment affected the number of nymphs that completed development, food consumption and whole-body lipid content. Additionally, both factors interactively determined female body mass. Our results highlight that insects may acquire and invest resources in a different manner when subjected to an intense interaction with conspecifics or when isolated. Furthermore, while only diet composition affected individual reproductive output, the social environment would determine the number of reproductive females, thus indirectly influencing population performance.

Cafeteria-style feeding trials provide new insights into the diet and nutritional strategies of the black snub-nosed monkey (Rhinopithecus strykeri): Implications for conservation

Anthropogenic changes and fragmentation of natural habitats often exert a negative effect on resource availability and distribution, and the nutritional ecology and feeding behavior of nonhuman primates. The goals of this study are to examine food choice and to identify the nutritional profile of foods consumed by the Critically Endangered black snub-nosed monkey (Rhinopithecus strykeri). To accomplish our study goals, we presented cafeteria-style feeding trials of fresh food items collected in the home range of wild black snub-nosed monkeys to the only two captive R. strykeri, and compared the nutritional profiles of the leafy foods (buds, young, and mature leaves, 100 i23tems from 70 plant species) selected with those avoided (54 items from 48 plant species). Overall, the results indicate that captive R. strykeri selected foods that were higher in moisture (Mo; 77.7%), crude protein (CP; 21.2%), total nonstructural carbohydrates (TNC; 34.9%), and phosphorus (P; 0.37%) while tending to avoid foods with a neutral detergent fiber (NDF) content of greater than 46.8%. Leaves collected in autumn and selected by the monkeys were characterized by a slightly higher amount of metabolizable energy (ME) than those rejected (1,350 kJ/100 g vs. 1,268 kJ/100 g). In contrast, the protein content of foods collected and consumed during the spring was greater (22.9%) than in autumn (16.4%). Random Forests modeling, an ensemble learning method, indicated that the proportion of Mo, NDF, ME, CP, P, and TNC were among the most important factors in predicting which items were consumed by the captive R. strykeri during spring and autumn. On the basis of the nutritional profile of foods consumed across the two seasons, we identified 18 nutrient-rich native plant species that we recommend for use in ex- and in-situ conservation management and reforestation programs to provide long-term access to a nutritionally adequate diet.

Wood and meat as complementary sources of sodium for Kanyawara chimpanzees (Pan troglodytes)

OBJECTIVES

Sodium, a vital micronutrient that is often in scarce supply for tropical herbivores, is sometimes found at high concentration in decaying wood. We tested two hypotheses for chimpanzees: first, that wood-eating facilitates acquisition of sodium; second, that wood-eating occurs in response to the low availability of sodium from other dietary sources.

MATERIALS AND METHODS

We studied the behavior of more than 50 chimpanzees of all age-sex classes in the Kanyawara community of Kibale National Park, Uganda. We quantified the sodium content of dietary items, including wood samples from tree species that chimpanzees consumed or did not consume. To assess variation in sodium intake, we used 7 years of data on time spent feeding on plant foods, 18 months of data on rates of food intake by adult females, and 20 years of data on meat-eating.

RESULTS

Major dietary sources of sodium were wood, fruits and meat. Chimpanzees consumed wood primarily from decaying trees of Neoboutonia macrocalyx (Euphorbiaceae), which had substantially higher sodium content than all other dietary items tested. Wood-eating was negatively correlated with fruit-eating. Females ate wood more often than males, while males had a greater probability of consuming meat at predation events.

DISCUSSION

We propose that females ate wood more often than males because females had reduced access to meat, their preferred source of sodium. This hypothesis suggests that the need for sodium is a motivating reason for chimpanzees to consume both meat and wood.

Pollen Protein: Lipid Macronutrient Ratios May Guide Broad Patterns of Bee Species Floral Preferences

Pollinator nutritional ecology provides insights into plant–pollinator interactions, coevolution, and the restoration of declining pollinator populations. Bees obtain their protein and lipid nutrient intake from pollen, which is essential for larval growth and development as well as adult health and reproduction. Our previous research revealed that pollen protein to lipid ratios (P:L) shape bumble bee foraging preferences among pollen host-plant species, and these preferred ratios link to bumble bee colony health and fitness. Yet, we are still in the early stages of integrating data on P:L ratios across plant and bee species. Here, using a standard laboratory protocol, we present over 80 plant species’ protein and lipid concentrations and P:L values, and we evaluate the P:L ratios of pollen collected by three bee species. We discuss the general phylogenetic, phenotypic, behavioral, and ecological trends observed in these P:L ratios that may drive plant–pollinator interactions; we also present future research questions to further strengthen the field of pollination nutritional ecology. This dataset provides a foundation for researchers studying the nutritional drivers of plant–pollinator interactions as well as for stakeholders developing planting schemes to best support pollinators.

The geography of grassland plant chemistry and productivity accounts for ant sodium and sugar usage

In Focus: Kaspari, M., Welti, E. A. R., & de Beurs, K. M. (2020). The nutritional geography of ants: Gradients of sodium and sugar limitation across North American grasslands. Journal of Animal Ecology, 89, 276-284. Biologically essential elements and macromolecules impact individuals to ecosystems and vary across space. Predictive frameworks for understanding community patterns across nutritional gradients are increasingly important as the nutritional landscape is continually altered by global change. Grasslands vary in the quantity and quality of essential nutrients that can impact plant consumer abundance, biomass and activity, but causes for variation, particularly across large spatial scales are poorly understood. In 53 North American grasslands spanning 16° latitude, Kaspari et al. (2020) tested three hypotheses for explaining sources of sodium (Na) limitation and five hypotheses for explaining sources of sugar limitation of ants, which are common and ecologically important omnivores that consume both plant- and animal-derived material. For both Na and sugar, over half of the variation in ant bait usage was accounted for by their predictions. Specifically, after accounting for ant activity (ant usage of sugar baits), ant Na-limitation was next best predicted by plant Na content and lastly, insect biomass, while sugar limitation after accounting for activity (ant usage of Na baits) was best predicted by growing season, then ecosystem productivity, plant potassium (K) and phosphorous (P), respectively. Kaspari et al. (2020) demonstrate the importance of plant physiology and chemistry towards a predictive framework for understanding sugar- and Na-limitation and highlights the importance of tackling ecological questions from a geographical perspective. This framework can provide a useful foundation for predicting future patterns in grassland organism nutritional ecology as plant species and physiology are altered with global change.

Host and symbiont genetic determinants of nutritional phenotype in a natural population of the pea aphid

A defining feature of the nutritional ecology of plant sap-feeding insects is that the dietary deficit of essential amino acids (EAAs) in plant sap is supplemented by EAA-provisioning microbial symbionts in the insect. Here, we demonstrated substantial variation in the nutritional phenotype of 208 genotypes of the pea aphid Acyrthosiphon pisum collected from a natural population. Specifically, the genotypes varied in performance (larval growth rates) on four test diets lacking the EAAs arginine, histidine and methionine or aromatic EAAs (phenylalanine and tryptophan), relative to the diet containing all EAAs. These data indicate that EAA supply from the symbiotic bacteria Buchnera can meet total aphid nutritional demand for only a subset of the EAA/aphid genotype combinations. We then correlated single nucleotide polymorphisms (SNPs) identified in the aphid and Buchnera genomes by reduced genome sequencing against aphid performance for each EAA deletion diet. This yielded significant associations between performance on the histidine-free diet and Buchnera SNPs, including metabolism genes predicted to influence histidine biosynthesis. Aphid genetic correlates of performance were obtained for all four deletion diets, with associations on the arginine-free diet and aromatic-free diets dominated by genes functioning in the regulation of metabolic and cellular processes. The specific aphid genes associated with performance on different EAA deletion diets are largely nonoverlapping, indicating some independence in the regulatory circuits determining aphid phenotype for the different EAAs. This study demonstrates how variation in the phenotype of associations collected from natural populations can be applied to elucidate the genetic basis of ecologically important traits in systems intractable to traditional forward/reverse genetic techniques.

The macronutrient composition of wild and cultivated plant foods of West African chimpanzees (Pan troglodytes verus) inhabiting an anthropogenic landscape

Agricultural expansion encroaches on tropical forests and primates in such landscapes frequently incorporate crops into their diet. Understanding the nutritional drivers behind crop-foraging can help inform conservation efforts to improve human-primate coexistence. This study builds on existing knowledge of primate diets in anthropogenic landscapes by estimating the macronutrient content of 24 wild and 11 cultivated foods (90.5% of food intake) consumed by chimpanzees (Pan troglodytes verus) at Bossou, Guinea, West Africa. We also compared the macronutrient composition of Bossou crops to published macronutrient measures of crops from Bulindi, Uganda, East Africa. The composition of wild fruits, leaves, and pith were consistent with previous reports for primate diets. Cultivated fruits were higher in carbohydrates and lower in insoluble fiber than wild fruits, while wild fruits were higher in protein. Macronutrient content of cultivated pith fell within the ranges of consumed wild pith. Oil palm food parts were relatively rich in carbohydrates, protein, lipids, and/or fermentable fiber, adding support for the nutritional importance of the oil palm for West African chimpanzees. We found no differences in the composition of cultivated fruits between Bossou and Bulindi, suggesting that macronutrient content alone does not explain differences in crop selection. Our results build on the current understanding of chimpanzee feeding ecology within forest-agricultural mosaics and provide additional support for the assumption that crops offer primates energetic benefits over wild foods.

The effect of intrinsic physiological traits on diapause survival and their underlying mechanisms in an annual bee species Bombus impatiens

In the face of insect declines, identifying phases of the life cycle when insects are particularly vulnerable to mortality is critical to conservation efforts. For numerous annual insect groups, diapause is both a key adaptation that allows survival of inhospitable conditions and a physiologically demanding life stage that can result in high rates of mortality. As bees continue to garner attention as a group experiencing high rates of decline, improving our understanding of how annual bees prepare for diapause and identifying factors that reduce survival is imperative. Here, we studied factors affecting diapause survival length and their underlying mechanisms using an economically and ecologically important annual bee species, Bombus impatiens. We examined how age and mass upon diapause onset correlate with diapause survival length, and the mechanistic role of nutrient acquisition and oxidative stress post pupal eclosion in mediating these effects. Our findings show that both age and mass were strong predictors of diapause survival length. Heavier queens or queens in the age range of ~6-17 days survived longer in diapause. Mass gain was attributed to increases in lipid, protein and glycerol amounts following pupal eclosion, and the ability to deal with oxidative stress was significantly compromised in older pre-diapause queens. Our results demonstrate that age-related shifts in bee physiology and timing of nutrient acquisition may both be critical factors driving diapause survival.

Playing it safe? Solitary vervet monkeys (Chlorocebus pygerythrus) choose high-quality foods more than those in competition

An important goal in foraging ecology is to determine how biotic and abiotic variables impact the foraging decisions of wild animals and how they move throughout their multidimensional landscape. However, the interaction of food quality and feeding competition on foraging decisions is largely unknown. Here we examine the importance of food quality in a patch on the foraging decisions of wild vervet monkeys (Chlorocebus pygerythrus) at Lake Nabugabo, Uganda using a multidestination platform array. The overall nutritional composition of the vervet diet was assessed and found to be low in sodium and lipids, thus we conducted a series of experimental manipulations in which the array was varied in salt and oil content. Although vervets prioritized platforms containing key nutrients (i.e., sodium and lipids) overall, we found that solitary vervets prioritized nutrient-dense platforms more strongly than competing vervets. This finding was opposite to those in a similar experiment that manipulated food site quantity, suggesting that large, salient rewards may be worth competing over but slight differences in nutritional density may be only chosen when there are no potentially negative social consequences (i.e., aggression received). We also found that vervets chose platforms baited with oil-only, and oil combined with salt, but not salt-only, suggesting that energy was an important factor in food choice. Our findings demonstrate that when wild vervets detect differences in feeding patches that reflect nutritional composition, they factor these differences into their navigational and foraging decisions. In addition, our findings suggest that these nutritional differences may be considered alongside social variables, ultimately leading to the complex strategies we observed in this study.