'Dust you shall eat': The complex nutritional and functional considerations underlying a simple diet.

Animals assimilate macronutrients and mineral nutrients in specific quantities and ratios to maximise fitness. To achieve this, animals must ingest different foods that contain the needed nutrients or facilitate the digestion of those nutrients. We explored how these multidimensional considerations affect the desert isopods (Hemilepistus reaumuri) curious food selection, using field and laboratory experiments. Wild isopods consumed three-fold more macronutrient-poor biological soil crust (BSC) than plant litter. Isopods tightly regulated macronutrient and calcium intake, but not phosphorus when eating the two natural foods and when artificial calcium and phosphorus sources substituted the BSC. Despite the equivalent calcium ingestion, isopods performed better when eating BSC compared to artificial foods. Isopods that consumed BSC sterilised by gamma-radiation ate more but grew slower than isopods that ate live BSC, implying that ingested microorganisms facilitate litter digestion. Our work highlights the need to reveal the multifaceted considerations that affect food-selection when exploring trophic-interactions.

Effects of macro- and micro-nutrients on momentary and season-long feeding responses by select species of ants.

Few studies have investigated the relative contribution of specific nutrients to momentary and season-long foraging responses by ants. Using western carpenter ants, Camponotus modoc, and European fire ants, Myrmica rubra, as model species, we: (1) tested preferential consumption of various macro- and micro-nutrients; (2) compared consumption of preferred macro-nutrients; (3) investigated seasonal shifts (late May to mid-September) in nutrient preferences; and (4) tested whether nutrient preferences of C. modoc and M. rubra pertain to black garden ants, Lasius niger, and thatching ants, Formica aserva. In laboratory and field experiments, we measured nutrient consumption by weighing Eppendorf tubes containing aqueous nutrient solutions before and after feeding by ants. Laboratory colonies of C. modoc favored nitrogenous urea and essential amino acids (EAAs), whereas M. rubra colonies favored sucrose. Field colonies of C. modoc and M. rubra preferentially consumed EAAs and sucrose, respectively, with no sustained shift in preferred macro-nutrient over the course of the foraging season. The presence of a less preferred macro-nutrient in a nutrient blend did not diminish the blend's 'appeal' to foraging ants. Sucrose and EAAs singly and in combination were equally consumed by L. niger, whereas F. aserva preferred EAAs. Baits containing both sucrose and EAAs were consistently consumed by the ants studied in this project and should be considered for pest ant control.

Diet and mitonuclear haplotype interactions affect growth rate in a slime mould.

Trait expression in metazoans is strongly influenced by the balance of macronutrients (i.e. protein, carbohydrate and fat) in the diet. At the same time, an individual's genetic background seems to regulate the magnitude of phenotypic response to a particular diet. It needs to be better understood whether interactions between diet, genetic background and trait expression are found in unicellular eukaryotes. A protist-the slime mould, Physarum polycephalum can choose diets based on protein-to-carbohydrate (P:C) content to support optimal growth rate. Yet, the role of genetic background (variation in the mitochondrial and nuclear DNAs) in mediating growth rate response to dietary P:C ratios in the slime mould is unknown. Here, we studied the effects of interactions between mitochondrial and nuclear DNA haplotypes and diet (i.e. G × G × E interactions) on the growth rate of P. polycephalum. A genetic panel of six distinct strains of P. polycephalum that differ in their mitochondrial and nuclear DNA haplotypes was used to measure growth rate across five diets that varied in their P:C ratio and total calories. We first determined the strains' growth rate (total biomass and surface area) when grown on a set menu with access to a particular diet. We then assessed whether the growth rate of strains increased on a buffet menu with access to all diets. Our findings show that the growth rate of P. polycephalum is generally higher on diets containing more carbohydrates than protein and that total calories negatively affect the growth rate. Three-way interactions between mitochondrial, nuclear haplotypes and dietary P:C ratios affected the strains' surface area of growth but not biomass. Intriguingly, strains did not increase their surface area and biomass when they had access to all diets on the buffet menu. Our findings have broad implications for our understanding of the effect of mitonuclear interactions on trait expression across diverse eukaryotic lineages.

The combined role of visual and olfactory cues in foraging by Cataglyphis ants in laboratory mazes.

Foragers use several senses to locate food, and many animals rely on vision and smell. It is beneficial not to rely on a single sense, which might fail under certain conditions. We examined the contribution of vision and smell to foraging and maze exploration under laboratory conditions using Cataglyphis desert ants as a model. Foraging intensity, measured as the number of workers entering the maze and arriving at the target as well as target arrival time, were greater when food, blue light, or both were offered or presented in contrast to a control. Workers trained to forage for a combined food and light cue elevated their foraging intensity with experience. However, foraging intensity was not higher when using both cues simultaneously than in either one of the two alone. Following training, we split between the two cues and moved either the food or the blue light to the opposite maze corner. This manipulation impaired foraging success by either leading to fewer workers arriving at the target cell (when the light stayed and the food was moved) or to more workers arriving at the opposite target cell, empty of food (when the food stayed and the light was moved). This result indicates that ant workers use both senses when foraging for food and readily associate light with food.

Ecological implications of fish removal: Insights from gut-content analysis of roach (Rutilus rutilus) and European perch (Perca fluviatilis) in a eutrophic shallow lake.

Large reductions in fish biomass are common both as a method of managing lake ecosystems by fish removals (biomanipulation) and as naturally occurring fish kills. To further understand how fish reductions change feeding patterns of fish, we studied the diets of small- to medium-sized roach (Rutilus rutilus) and European perch (Perca fluviatilis) on a monthly basis using gut-content analysis during an 18-month period before and after a whole-lake fish removal in a eutrophic shallow lake. Further, we performed in-depth analyses of zoobenthos communities of the profundal and littoral zones, as well as analysed the zooplankton community in the littoral and pelagic parts of the lake to estimate abundance and biomass of potential diet items. We found that, in general, there was a trend toward increased zoobenthivory in both species and among all-sized fish after fish removal, regardless of prior diet preference. Reduced piscivory among larger perch (>150 mm) and reduced zooplanktivory among smaller perch and roach (<150 mm) were also observed. Moreover, during a short period of high zooplankton biomass after fish removal, both perch and roach (all sizes) shifted their diet toward daphnids, which likely caused a decrease in daphnid population. We suggest that such change toward periodical zooplanktivory across fish species and size groups may lead to unexpectedly high top-down control by fish after lake restoration by fish removal.

Strategy maps: Generalised giving-up densities for optimal foraging.

Finding a common currency for benefits and hazards is a major challenge in optimal foraging theory, often requiring complex computational methods. We present a new analytic approach that builds on the Marginal Value Theorem and giving-up densities while incorporating the nonlinear effect of predation risk. We map the space of all possible environments into strategy regions, each corresponding to a discrete optimal strategy. This provides a generalised quantitative measure of the trade-off between foraging rewards and hazards. This extends a classic optimal diet choice rule-of-thumb to incorporate the hazard of waiting for better resources to appear. We compare the dynamics of optimal decision-making for three foraging life-history strategies: One in which fitness accrues instantly, and two with delays before fitness benefit is accrued. Foragers with delayed-benefit strategies are more sensitive to predation risk than resource quality, as they stand to lose more fitness from a predation event than instant-accrual foragers.

Ecological lipidology.

Dietary lipids (DLs), particularly sterols and fatty acids, are precursors for endogenous lipids that, unusually for macronutrients, shape cellular and organismal function long after ingestion. These functions - cell membrane structure, intracellular signalling, and hormonal activity - vary with the identity of DLs, and scale up to influence health, survival, and reproductive fitness, thereby affecting evolutionary change. Our Ecological Lipidology approach integrates biochemical mechanisms and molecular cell biology into evolution and nutritional ecology. It exposes our need to understand environmental impacts on lipidomes, the lipid specificity of cell functions, and predicts the evolution of lipid-based diet choices. Broad interdisciplinary implications of Ecological Lipidology include food web alterations, species responses to environmental change, as well as sex differences and lifestyle impacts on human nutrition, and opportunities for DL-based therapies.

Differences in Dietary Intake Exist among U.S. Adults by Diabetic Status Using NHANES 2009-2016.

The objective was to determine the most frequently consumed food items, food subcategories, and food categories, and those that contributed most to total energy intake for the group of U.S. adults reporting taking insulin, those with type 2 diabetes (T2D) not taking insulin, and those without diabetes. Laboratory tests and questionnaires of the National Health and Nutrition Examination Survey 2009-2016 classified 774 participants reporting taking insulin, 2758 participants reporting T2D not taking insulin, and 17,796 participants without diabetes. Raw and weighted frequency and energy contributions of each food item, food subcategory, and food category were calculated and ranked. Comparisons among groups by broad food category used the Rao-Scott modified chi-square test. Soft drinks ranked as the 8th and 6th most consumed food subcategory of participants with T2D not taking insulin and those without diabetes, and contributed 5th and 2nd most to energy, respectively. The group reporting taking insulin is likely to consume more protein foods and less soft drink compared to the other two groups. Lists of the most frequently reported foods and foods contributing most to energy may be helpful for nutrition education, prescribing diets, and digital-based dietary assessment for the group reporting taking insulin.

The gut microbiome influences host diet selection behavior.

Diet selection is a fundamental aspect of animal behavior with numerous ecological and evolutionary implications. While the underlying mechanisms are complex, the availability of essential dietary nutrients can strongly influence diet selection behavior. The gut microbiome has been shown to metabolize many of these same nutrients, leading to the untested hypothesis that intestinal microbiota may influence diet selection. Here, we show that germ-free mice colonized by gut microbiota from three rodent species with distinct foraging strategies differentially selected diets that varied in macronutrient composition. Specifically, we found that herbivore-conventionalized mice voluntarily selected a higher protein:carbohydrate (P:C) ratio diet, while omnivore- and carnivore-conventionalized mice selected a lower P:C ratio diet. In support of the long-standing hypothesis that tryptophan­the essential amino acid precursor of serotonin­serves as a peripheral signal regulating diet selection, bacterial genes involved in tryptophan metabolism and plasma tryptophan availability prior to the selection trial were significantly correlated with subsequent voluntary carbohydrate intake. Finally, herbivore-conventionalized mice exhibited larger intestinal compartments associated with microbial fermentation, broadly reflecting the intestinal morphology of their donor species. Together, these results demonstrate that gut microbiome can influence host diet selection behavior, perhaps by mediating the availability of essential amino acids, thereby revealing a mechanism by which the gut microbiota can influence host foraging behavior.

Artificial selection for predatory behaviour results in dietary niche differentiation in an omnivorous mammal.

The diet of an individual is a result of the availability of dietary items and the individual's foraging skills and preferences. Behavioural differences may thus influence diet variation, but the evolvability of diet choice through behavioural evolution has not been studied. We used experimental evolution combined with a field enclosure experiment to test whether behavioural selection leads to dietary divergence. We analysed the individual dietary niche via stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) in the hair of an omnivorous mammal, the bank vole, from four lines selected for predatory behaviour and four unselected control lines. Predatory voles had higher hair δ15N values than control voles, supporting our hypothesis that predatory voles would consume a higher trophic level diet (more animal versus plant foods). This difference was significant in the early but not the late summer season. The δ13C values also indicated a seasonal change in the consumed plant matter and a difference in food sources among selection lines in the early summer. These results imply that environmental factors interact with evolved behavioural tendencies to determine dietary niche heterogeneity. Behavioural selection thus has potential to contribute to the evolution of diet choice and ultimately the species' ecological niche breadth.

Altering salivary protein profile can decrease aversive oromotor responding to quinine in rats.

Bitter taste is often associated with toxins, but accepting some bitter foods, such as green vegetables, can be an important part of maintaining a healthy diet. It has previously been shown that animals exposed to quinine upregulate a set of salivary proteins (SPs), and those with upregulated SPs have increased rates of feeding on a quinine diet as well as increased brief-access licking to and higher detection thresholds for quinine. These studies suggest that SPs alter orosensory feedback; however, they rely on SPs upregulated by diet exposure and cannot control for the role of learning. Here, we use taste reactivity to determine if SPs can alter bitter taste in animals with no previous bitter diet experience. First, saliva with proteins stimulated by injections of isoproterenol and pilocarpine was collected from anesthetized rats; this "donor saliva" was analyzed for protein concentration and profile. Bitter-naïve rats were implanted with oral catheters and infused with taste stimuli dissolved in saliva that contained all of the SPs from the donors, saliva that was filtered of SPs, water, or artificial saliva. Their orofacial movements were recorded and quantified. We found that presence of quinine increased movements associated with aversive stimuli, but adding SPs to the infusion was sufficient to reduce aversive oromotor responding to quinine. The effect was dependent on the total protein concentration of the saliva, as protein concentration increased aversive responses decreased. Additionally, infusions of whole saliva altered aversive responding to quinine, but not other stimuli (citric acid, NaCl, sucrose). Our work suggests that effect of these SPs is specific and the presence of SPs is sufficient to decrease aversive orosensory feedback to bitter stimuli.

Revisiting the "fallacy of averages" in ecology: Expected gain per unit time equals expected gain divided by expected time.

Fitness is often defined as the average payoff an animal obtains when it is engaged in several activities, each taking some time. We point out that the average can be calculated with respect to either the time distribution, or to the event distribution of these activities. We show that these two averages lead to the same fitness function. We illustrate this result through two examples from foraging theory, Holling II functional response and the diet choice model, and one game-theoretic example of Hamilton's rule applied to the time-constrained Prisoner's dilemma (PD). In particular, we show that in these models, fitness defined as expected gain per unit time equals fitness defined as expected gain divided by expected time. We also show how these fitnesses predict the optimal outcome for diet choice and the prevalence of cooperation in the repeated PD game.

Predation risk influences food-web structure by constraining species diet choice.

The foraging behaviour of species determines their diet and, therefore, also emergent food-web structure. Optimal foraging theory (OFT) has previously been applied to understand the emergence of food-web structure through a consumer-centric consideration of diet choice. However, the resource-centric viewpoint, where species adjust their behaviour to reduce the risk of predation, has not been considered. We develop a mechanistic model that merges metabolic theory with OFT to incorporate the effect of predation risk on diet choice to assemble food webs. This 'predation-risk-compromise' (PR) model better captures the nestedness and modularity of empirical food webs relative to the classical optimal foraging model. Specifically, compared with optimal foraging alone, risk-mitigated foraging leads to more-nested but less-modular webs by broadening the diet of consumers at intermediate trophic levels. Thus, predation risk significantly affects food-web structure by constraining species' ability to forage optimally, and needs to be considered in future work.

Negative frequency-dependent foraging behaviour in a generalist herbivore (Alces alces) and its stabilizing influence on food web dynamics.

Resource selection is widely appreciated to be context-dependent and shaped by both biological and abiotic factors. However, few studies have empirically assessed the extent to which selective foraging behaviour is dynamic and varies in response to environmental conditions for free-ranging animal populations. Here, we assessed the extent that forage selection fluctuated in response to different environmental conditions for a free-ranging herbivore, moose (Alces alces), in Isle Royale National Park, over a 10-year period. More precisely, we assessed how moose selection for coniferous versus deciduous forage in winter varied between geographic regions and in relation to (a) the relative frequency of forage types in the environment (e.g. frequency-dependent foraging behaviour), (b) moose abundance, (c) predation rate (by grey wolves) and (d) snow depth. These factors are potentially important for their influence on the energetics of foraging. We also built a series of food-chain models to assess the influence of dynamic foraging strategies on the stability of food webs. Our analysis indicates that moose exhibited negative frequency dependence, by selectively exploiting rare resources. Frequency-dependent foraging was further mediated by density-dependent processes, which are likely to be predation, moose abundance or some combination of both. In particular, frequency dependence was weaker in years when predation risk was high (i.e. when the ratio of moose to wolves was relatively low). Selection for conifers was also slightly weaker during deep snow years. The food-chain analysis indicates that the type of frequency-dependent foraging strategy exhibited by herbivores had important consequences for the stability of ecological communities. In particular, the dynamic foraging strategy that we observed in the empirical analysis (i.e. negative frequency dependence being mediated by density-dependent processes) was associated with more stable food web dynamics compared to fixed foraging strategies. The results of this study indicated that forage selection is a complex ecological process, varying in response to both biological (predation and moose density) and abiotic factors (snow depth) and over relatively small spatial scales (between regions). This study also provides a useful framework for assessing the influence of other aspects of foraging behaviour on the stability of food web dynamics.

Choices between red clover and fescue in the diet can be reliably estimated in heifers post-weaning using n-alkanes.

Measuring diet choice in grazing animals is challenging, complicating the assessment of feed efficiency in pasture-based systems. Furthermore, animals may modify their intake of a forage species depending on its nutritive value and on their own physiological status. Various fecal markers have been used to estimate feed intake in grazing animals. However, plant-wax markers such as n-alkanes (ALK) and long-chain alcohols may provide reliable estimates of both dietary choices and intakes. Still, their use in beef cattle has been relatively limited. The present study was designed to test the reliability of the ALK technique to estimate diet choices in beef heifers. Twenty-two Angus-cross heifers were evaluated at both post-weaning and yearling age. At each age, they were offered both red clover and fescue hay as cubes. Following 3-week acclimation periods, daily intake of each forage species was assessed daily for 10 days. During the final 5 days, fecal grab samples were collected twice daily. The ALK fecal concentrations were adjusted using recovery fractions compiled from literature. Diet composition was estimated using two statistical methods. Post-weaning, dietary choices were reliably estimated, with low residual error, regardless of the statistical approach adopted. The regression of observed on estimated red clover proportion ranged from 0.85±0.08 to 1.01±0.09 for fecal samples collected in the p.m. and for daily proportions once averaged, respectively. However, at yearling age, the estimates were less reliable. There was a tendency to overestimate the red clover proportion in diets of heifers preferring fescue, and vice versa. This was due to greater variability in ALK fecal concentrations in the yearling heifers. Overall, the ALK technique provided a reliable tool for estimating diet choice in animals fed a simple forage diet. Although further refinements in the application of this methodology are needed, plant-wax markers provide opportunities for evaluating diet composition in grazing systems in cattle.

Altering salivary protein profile can increase acceptance of a novel bitter diet.

Bitter taste is often associated with toxins, but accepting some bitter foods, such as green vegetables, can be an important part of maintaining a healthy diet. In rats and humans, repeated exposure to a bitter stimulus increases acceptance. Repeated exposure allows an individual the opportunity to learn about the food's orosensory and postingestive effects. It also alters the salivary protein (SP) profile, which in turn alters taste signaling. We have hypothesized that altering the salivary proteome plays a role in the increased acceptance after repeated exposure. Here we test this and attempt to disentangle the contribution of learning during dietary exposure from the contribution of SPs in increased acceptance of bitter diet. Dietary exposure to quinine or tannic acid and injection of isoproterenol (IPR) result in similar salivary protein profiles. Here we used either the bitter stimulus tannic acid or IPR injection to upregulate a subset of SPs before exposing animals to a novel diet containing quinine (0.375%). Control animals received either a control diet before being exposed to quinine, or a diet containing sucrose octaacetate, a compound that the animals avoid but does not alter SP profiles. The treatments that alter SP expression increased rate of feeding on the quinine diet compared to the control treatments. Additionally, tannic acid exposure altered intake and meal size of the quinine diet. These data suggest that SPs, not just learning about bitter food, increase acceptance of the bitter diet.

Should I shoot or should I go? Simple rules for prey selection in multi-species hunting systems.

Across the tropics, unregulated hunting targeting many different species presents a major conservation challenge. Prioritizing resources for monitoring and enforcement is difficult when multiple prey species are exploited. However, identifying which prey species are subject to hunting pressure can be achieved with diet choice models. We evaluate hunter diet sets using data from Southwest China and compare two diet choice models: optimal foraging theory and a relatively new diet model originating from economic optimal stopping problems. The optimal stopping diet choice model required fewer field parameters than optimal foraging models and more accurately reflected hunter catch in Southwest China. The optimal stopping model also indicated that hunters should be less selective when they experience a larger opportunity cost for their time. Finally, we illustrate a new method to evaluate harvest impact from single sites with limited data using dietary thresholds. This technique could be used to evaluate whether or not the community of exploited wildlife has shifted in its trait distribution, providing a means to anticipate trait-biased defaunation from minimal data.

Neural and Molecular Mechanisms Involved in Controlling the Quality of Feeding Behavior: Diet Selection and Feeding Patterns.

We are what we eat. There are three aspects of feeding: what, when, and how much. These aspects represent the quantity (how much) and quality (what and when) of feeding. The quantitative aspect of feeding has been studied extensively, because weight is primarily determined by the balance between caloric intake and expenditure. In contrast, less is known about the mechanisms that regulate the qualitative aspects of feeding, although they also significantly impact the control of weight and health. However, two aspects of feeding quality relevant to weight loss and weight regain are discussed in this review: macronutrient-based diet selection (what) and feeding pattern (when). This review covers the importance of these two factors in controlling weight and health, and the central mechanisms that regulate them. The relatively limited and fragmented knowledge on these topics indicates that we lack an integrated understanding of the qualitative aspects of feeding behavior. To promote better understanding of weight control, research efforts must focus more on the mechanisms that control the quality and quantity of feeding behavior. This understanding will contribute to improving dietary interventions for achieving weight control and for preventing weight regain following weight loss.

Application of diet theory reveals context-dependent foraging preferences in an herbivorous coral reef fish.

Dietary preferences of grazers can drive spatial variability in top-down control of autotroph communities, because diet composition may depend on the relative availability of autotroph species. On Caribbean coral reefs, parrotfish grazing is important in limiting macroalgae, but parrotfish dietary preferences are poorly understood. We applied diet-switching analysis to quantify the foraging preferences of the redband parrotfish (Sparisoma aurofrenatum). At 12 Caribbean reefs, we observed 293 redband parrotfish in 5-min feeding bouts and quantified relative benthic algal cover using quadrats. The primary diet items were macroalgal turfs, Halimeda spp., and foliose macroalgae (primarily Dictyota spp. and Lobophora spp.). When each resource was evaluated independently, there were only weak relationships between resource cover and foraging effort (number of bites taken). Electivity for each resource also showed no pattern, varying from positive (preference for the resource) to negative (avoidance) across sites. However, a diet-switching analysis consisting of pairwise comparisons of relative cover and relative foraging effort revealed clearer patterns: parrotfish (a) preferred Halimeda and macroalgal turfs equally, and those two resources were highly substitutable; (b) preferred Halimeda to foliose macroalgae, but those two resources were complementary; and (c) also preferred turf to foliose macroalgae, and those resources were also complementary. Thus parrotfish grazing rates depend on relative, not absolute, abundance of macroalgal types, due to differences in substitutability among resources. Application of similar analyses may help predict potential changes in foraging effort of benthic grazers over spatial gradients that could inform expectations for reef recovery following the protection of herbivore populations.

Bridge under troubled water: Turbulence and niche partitioning in fish foraging.

The coexistence of competing species relies on niche partitioning. Competitive exclusion is likely inevitable at high niche overlap, but such divide between competitors may be bridged if environmental circumstances displace competitor niches to enhance partitioning. Foraging-niche dimension can be influenced by environmental characteristics, and if competitors react differently to such conditions, coexistence can be facilitated. We here experimentally approach the partitioning effects of environmental conditions by evaluating the influence of water turbulence on foraging-niche responses in two competing fish species, Eurasian perch Perca fluviatilis and roach Rutilus rutilus, selecting from planktonic and benthic prey. In the absence of turbulence, both fish species showed high selectivity for benthic chironomid larvae. R. rutilus fed almost exclusively on zoobenthos, whereas P. fluviatilis complemented the benthic diet with zooplankton (mainly copepods). In turbulent water, on the other hand, the foraging-niche widths of both R. rutilus and P. fluviatilis increased, while their diet overlap simultaneously decreased, caused by 20% of the R. rutilus individuals turning to planktonic (mainly bosminids) prey, and by P. fluviatilis increasing foraging on littoral/benthic food sources. We show that moderate physical disturbance of environments, such as turbulence, can enhance niche partitioning and thereby coexistence of competing foragers. Turbulence affects prey but not fish swimming capacities, with consequences for prey-specific distributions and encounter rates with fish of different foraging strategies (pause-travel P. fluviatilis and cruise R. rutilus). Water turbulence and prey community structure should hereby affect competitive interaction strengths among fish species, with consequences for coexistence probability as well as community and system compositions.