Formica fusca ants use aphid supplemented foods to alleviate effects during the acute phase of a fungal infection.

The modulation of nutritional intake by animals to combat pathogens is a behaviour that is receiving increasing attention. Ant studies using isolated compounds or nutrients in artificial diets have revealed a lot of the dynamics of the behaviour, but natural sources of medicine are yet to be confirmed. Here we explored whether Formica fusca ants exposed to a fungal pathogen can use an artificial diet containing foods spiked with different concentrations of crushed aphids for a medicinal benefit. We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented foods during the acute phase of the infection, reducing the mortality caused by the disease. However, the benefit was only attained when having access to a varied diet, suggesting that while aphids contain nutrients or compounds beneficial against infection, it is a part of a complex nutritional system where costs and benefits of compounds and nutrients need to be moderated.

Salt has contrasting effects on the digestive processing of dilute nectar by two Neotropical nectarivorous bats.

Nectarivorous vertebrates might include sugar-dilute nectar in their diet and they are expected to undergo compensatory feeding. However, physiological constraints might limit the intake of sugar-dilute nectar, affecting energy budgets. Among other physiological processes, the limiting role of osmoregulation is supported by enhanced intake rate of dilute sugar solutions by avian nectarivores when salt is added. We tested if the Greater Antillean Long-tongued bat (Monophyllus redmani) and the Brown flower bat (Erophylla sezekorni) compensated energy intake when fed dilute-sugar solutions (2.5 and 5% sucrose), and if salt content (11, 20 and 40 mM NaCl l-1) modulated the intake rate of these solutions. Both species were unable to compensate intake of solutions with varying sugar densities, and energy intake on the 2.5 and 5% diets was lower than on the most concentrated diets (10, 20 and 30% sucrose). Both species responded differently to the addition of salt. Salt addition did not affect the intake of 2.5% sugar solutions by the Greater Antillean Long-tongued bat, and it decreased the intake of 5% sugar solutions. In contrast, the Brown flower bat increased the intake of 2.5 and 5% sugar solutions when salt was added. Intake responses to varying sugar densities of our two focal species and that of other bat species previously studied indicate that they are not uniform and that they might be modulated by digestive and osmoregulatory physiological traits.

Herbivore consumers face different challenges along opposite sides of the stoichiometric knife-edge.

Anthropogenic activities have reshaped the relative supply rates of essential elements to organisms. Recent studies suggested that consumer performance is strongly reduced by food that is either very high or very low in relative phosphorus content. However, the generality of such 'stoichiometric knife-edge' and its underlying mechanisms are poorly understood. We studied the response of a planktonic rotifer to a 10-fold food carbon : phosphorus (C : P) gradient and confirmed the existence of the stoichiometric knife-edge. Interestingly, we observed a complete homeostatic breakdown associated with strong growth reductions at high food C : P. In contrast, at low food C : P, animals maintained homeostasis despite pronounced performance reductions. Our results suggest that the mechanisms underlying adverse effects of stoichiometric imbalance are determined by both the identity of elements that are limiting and those that are present in excess. Negative effects of excess P reveal an additional way of how eutrophication may affect consumers.

Understanding the stoichiometric limitation of herbivore growth: the importance of feeding and assimilation flexibilities.

Ecological stoichiometry suggests that herbivore growth is limited by phosphorus when this element in the diet is < 8.6 µg P mg C-1 (C : P atomic ratio > 300). However, in nature, it is not necessarily related to the relative phosphorus content in diets. This may be the result of complex feeding and assimilation responses to diets. We examined these possibilities using herbivorous plankton fed mono-specific and mixed algae varying in phosphorus content of 1.6 to 8.1 µg P mg C-1 . The herbivores showed a 10-fold growth rate difference among the diets. Growth rates related poorly with phosphorus content in the diets (r2  = 0.07), better with P ingestion rate (r2  = 0.41) and best with phosphorus assimilation rate (r2  = 0.69). Inclusion of assimilation rates for carbon and fatty acids increased 7% of the explained growth variance. These results indicate that the feeding and assimilation flexibilities play pivotal roles in acquiring a deficient element and in regulating growth rate.

Immanent conditions determine imminent collapses: nutrient regimes define the resilience of macroalgal communities.

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m-2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer-resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.

Parasite-altered feeding behavior in insects: integrating functional and mechanistic research frontiers.

Research on parasite-altered feeding behavior in insects is contributing to an emerging literature that considers possible adaptive consequences of altered feeding behavior for the host or the parasite. Several recent ecoimmunological studies show that insects can adaptively alter their foraging behavior in response to parasitism. Another body of recent work shows that infection by parasites can change the behavior of insect hosts to benefit the parasite; manipulations of host feeding behavior may be part of this phenomenon. Here, we address both the functional and the underlying physiological frontiers of parasite-altered feeding behavior in order to spur research that better integrates the two. Functional categories of parasite-altered behavior that are adaptive for the host include prophylaxis, therapy and compensation, while host manipulation is adaptive for the parasite. To better understand and distinguish prophylaxis, therapy and compensation, further study of physiological feedbacks affecting host sensory systems is especially needed. For host manipulation in particular, research on mechanisms by which parasites control host feedbacks will be important to integrate with functional approaches. We see this integration as critical to advancing the field of parasite-altered feeding behavior, which may be common in insects and consequential for human and environmental health.

High dietary quality of non-toxic cyanobacteria for a benthic grazer and its implications for the control of cyanobacterial biofilms.

BACKGROUND: Mass occurrences of cyanobacteria frequently cause detrimental effects to the functioning of aquatic ecosystems. Consequently, attempts haven been made to control cyanobacterial blooms through naturally co-occurring herbivores. Control of cyanobacteria through herbivores often appears to be constrained by their low dietary quality, rather than by the possession of toxins, as also non-toxic cyanobacteria are hardly consumed by many herbivores. It was thus hypothesized that the consumption of non-toxic cyanobacteria may be improved when complemented with other high quality prey. We conducted a laboratory experiment in which we fed the herbivorous freshwater gastropod Lymnaea stagnalis single non-toxic cyanobacterial and unialgal diets or a mixed diet to test if diet-mixing may enable these herbivores to control non-toxic cyanobacterial mass abundances. RESULTS: The treatments where L. stagnalis were fed non-toxic cyanobacteria and a mixed diet provided a significantly higher shell and soft-body growth rate than the average of all single algal, but not the non-toxic cyanobacterial diets. However, the increase in growth provided by the non-toxic cyanobacteria diets could not be related to typical determinants of dietary quality such as toxicity, nutrient stoichiometry or essential fatty acid content. CONCLUSIONS: These results strongly contradict previous research which describes non-toxic cyanobacteria as a low quality food resource for freshwater herbivores in general. Our findings thus have strong implications to gastropod-cyanobacteria relationships and suggest that freshwater gastropods may be able to control mass occurrences of benthic non-toxic cyanobacteria, frequently observed in eutrophied water bodies worldwide.

Boom and bust: rapid feedback responses between insect outbreak dynamics and canopy leaf area impacted by rainfall and CO2.

Frequency and severity of insect outbreaks in forest ecosystems are predicted to increase with climate change. How this will impact canopy leaf area in future climates is rarely tested. Here, we document function of insect outbreaks that fortuitously and rapidly occurred in an ecosystem under free-air CO2 enrichment. Over the first 2 years of CO2 fumigation of a naturally established mature Eucalyptus woodland, we continuously assessed population responses of three sap-feeding insect species of the psyllid genera Cardiaspina, Glycaspis and Spondyliaspis for up to ten consecutive generations. Concurrently, we quantified changes in the canopy leaf area index (LAI). Large and rapid shifts in psyllid community composition were recorded between species with either flush (Glycaspis) or senescence-inducing (Cardiaspina, Spondyliaspis) feeding strategies. Within the second year, two psyllid species experienced significant and rapid population build-up resulting in two consecutive outbreaks: first, rainfall stimulated Eucalyptus leaf production increasing LAI, which supported population growth of flush-feeding Glycaspis without impacting LAI. Glycaspis numbers then crashed and were followed by the outbreak of senescence-feeding Cardiaspina fiscella that led to significant defoliation and reduction in LAI. For all three psyllid species, the abundance of lerps, protective coverings excreted by the sessile nymphs, decreased at e[CO2 ]. Higher lerp weight at e[CO2 ] for Glycaspis but not the other psyllid species provided evidence for compensatory feeding by the flush feeder but not the two senescence feeders. Our study demonstrates that rainfall drives leaf phenology, facilitating the rapid boom-and-bust succession of psyllid species, eventually leading to significant defoliation due to the second but not the first outbreaking psyllid species. In contrast, e[CO2 ] may impact psyllid abundance and feeding behaviour, with psyllid species-specific outcomes for defoliation severity, nutrient transfer and trophic cascades. Psyllid populations feeding on Eucalyptus experience rapid boom-and-bust cycles depending on availability of suitable foliage driven by rainfall patterns and leaf phenology.

Will chemical defenses become more effective against specialist herbivores under elevated CO2?

Elevated atmospheric CO2 is known to affect plant-insect herbivore interactions. Elevated CO2 causes leaf nitrogen to decrease, the ostensible cause of herbivore compensatory feeding. CO2 may also affect herbivore consumption by altering chemical defenses via changes in plant hormones. We considered the effects of elevated CO2, in conjunction with soil fertility and damage (simulated herbivory), on glucosinolate concentrations of mustard (Brassica nigra) and collard (B. oleracea var. acephala) and the effects of leaf nitrogen and glucosinolate groups on specialist Pieris rapae consumption. Elevated CO2 affected B. oleracea but not B. nigra glucosinolates; responses to soil fertility and damage were also species-specific. Soil fertility and damage also affected B. oleracea glucosinolates differently under elevated CO2. Glucosinolates did not affect P. rapae consumption at either CO2 concentration in B. nigra, but had CO2-specific effects on consumption in B. oleracea. At ambient CO2, leaf nitrogen had strong effects on glucosinolate concentrations and P. rapae consumption but only gluconasturtiin was a feeding stimulant. At elevated CO2, direct effects of leaf nitrogen were weaker, but glucosinolates had stronger effects on consumption. Gluconasturtiin and aliphatic glucosinolates were feeding stimulants and indole glucosinolates were feeding deterrents. These results do not support the compensatory feeding hypothesis as the sole driver of changes in P. rapae consumption under elevated CO2. Support for hormone-mediated CO2 response (HMCR) was mixed; it explained few treatment effects on constitutive or induced glucosinolates, but did explain patterns in SEMs. Further, the novel feeding deterrent effect of indole glucosinolates under elevated CO2 in B. oleracae underscores the importance of defensive chemistry in CO2 response. We speculate that P. rapae indole glucosinolate detoxification mechanisms may have been overwhelmed under elevated CO2 forcing slowed consumption. Specialists may have to contend with hosts with poorer nutritional quality and more effective chemical defenses under elevated CO2.

Effect of low levels of Bacillus thuringiensis exposure on the growth, food consumption and digestion efficiencies of Trichoplusia ni resistant and susceptible to Bt.

It is becoming increasingly clear that the impact of low doses of an environmental stressor, such as Bacillus thuringiensis, can often not be predicted from high dose experiments, and the impact of these effects on the evolution of resistance has received little attention. In the present study, we examined the effect of low levels of B. thuringiensis exposure on the growth, food consumption and digestion efficiencies of Trichoplusia ni resistant and susceptible to Bt. Larvae were fed on specified Bt concentrations continually for 3 days. Resistant larvae exhibited increases in diet consumption, weight gain and conversion of ingested food to biomass in response to feeding continually on some of the Bt concentrations. The positive effect of feeding on low levels of Bt on the growth of resistant larvae was modulated by initial larval size and the amount of food consumed. In contrast, susceptible larvae exhibited reductions in growth and frass production at all tested Bt concentrations. Further studies are needed to determine the role of accelerated growth on the evolution of Bt resistance in T. ni populations and to evaluate the importance of life-history responses to sublethal concentrations in the context of insecticide resistance management.

Diet variation of a generalist fish predator, grey snapper Lutjanus griseus, across an estuarine gradient: trade-offs of quantity for quality?

This study examined diet, prey quality and growth for a generalist fish predator, grey snapper Lutjanus griseus, at five sites across an estuarine gradient in the Loxahatchee River estuary, Florida, U.S.A. Lutjanus griseus diets shifted from dominance by low quality, intertidal crabs upstream to an increased reliance on higher quality shrimp, fishes and benthic crabs downstream. Frequency of L. griseus with empty stomachs was higher at downstream sites. Lutjanus griseus growth rates did not vary among sites. Results indicate that L. griseus may be able to compensate for lower quality prey upstream by consuming more, and thus individuals are able to maintain similar levels of energy balance and growth rates across the estuarine gradient. Elucidating mechanisms, such as compensatory feeding, that enable generalist species to remain successful across habitat conditions are critical to understanding their organismal ecology and may facilitate predictions about the response of generalists to landscape alteration.

Effects of dietary crude protein levels in the concentrate supplement after grazing on rumen microbiota and metabolites by using metagenomics and metabolomics in Jersey-yak.

Introduction: The crude protein level in the diet will affect the fermentation parameters, microflora, and metabolites in the rumen of ruminants. It is of great significance to study the effect of crude protein levels in supplementary diet on microbial community and metabolites for improving animal growth performance. At present, the effects of crude protein level in supplementary diet on rumen fermentation parameters, microbial community, and metabolites of Jersey-Yak (JY) are still unclear. Methods: The purpose of this experiment was to study the appropriate crude protein level in the diet of JY. The rumen fermentation indexes (volatile fatty acids and pH) were determined by supplementary diets with crude protein levels of 15.16 and 17.90%, respectively, and the microbial community and metabolites of JYs were analyzed by non-target metabonomics and metagenome sequencing technology, and the changes of rumen fermentation parameters, microbial flora, and metabolites in the three groups and their interactions were studied. Results and Discussion: The crude protein level in the supplementary diet had significant effects on pH, valeric acid, and the ratio of acetic acid to propionic acid (p < 0.05). The protein level had no significant effect on the dominant microflora at the phylum level (p > 0.05), and all three groups were Bacteroides and Firmicutes. The results of metabolite analysis showed that the crude protein level of supplementary diet significantly affected the metabolic pathways such as Bile secretion and styrene degradation (p < 0.05), and there were different metabolites between the LP group and HP group, and these different metabolites were related to the dominant microbial to some extent. To sum up, in this experiment, the effects of crude protein level in supplementary diet on rumen microorganisms and metabolites of JY and their relationship were studied, which provided the theoretical basis for formulating a more scientific and reasonable supplementary diet in the future.

Impact of Biochar on Douglas-Fir Tussock Moth (Orgyia pseudotsugata Lepidoptera: Erebidae) Larvae Reared on Synthetic Diet.

The use of biochar as a soil amendment in forest ecosystems can be beneficial in the restoration of degraded soils. Forest insects such as the Douglas-fir tussock moth, Orgyia pseudotsugata (McDonnough) (Lepidoptera: Erebidae), may be exposed to biochar when the material is applied. Two experiments were conducted using biochar either (1) applied to the surface of the diet at three rates (0, 5, and 10 mg) or (2) incorporated into synthetic diet at four rates (0, 10, 20, and 40% volume/volume). The objective of both experiments was to determine if biochar on the surface or incorporated into a synthetic diet affected development and survival of O. pseudotsugata larvae. In both experiments, there was a significant decrease in estimated time to larval mortality in all biochar treatments compared to untreated controls. In the surface-applied biochar experiment, there was a significant difference in larval weight gain at day 12 between the control and 10 mg biochar treatments. In the experiment with biochar incorporated into the diet, mean larval weight at day 12 was highest in the low (10%) biochar treatment compared to all other treatments, although weight gain was only significantly different between the low- and high-concentration (40%) biochar treatments. Our results suggest that larvae, feeding on a low amount of biochar in the synthetic diet, may respond by engaging in compensatory feeding behavior. Fewer surviving larvae in the biochar treatment groups may contribute to the lack of significance found in the comparison of weight gain at day 24 in each experiment.

Life on the edge: Compensatory growth and feeding rates at environmental extremes mediates potential ecosystem engineering by an invasive bivalve.

Invasive non-native species (INNS) with marine or brackish origins have become increasingly common occupying freshwater habitats. The transition of INNS from marine or brackish water into physiologically stressful freshwater environments may be facilitated by compensatory growth and elevated feeding rates. In this study, we investigate the capacity of the Gulf wedge clam (Rangia cuneata), a brackish NNS that is spreading quickly across European waterways, to survive in freshwater conditions and consider its resultant impacts as an ecosystem engineer. To investigate the performance of R. cuneata under freshwater conditions, we compared the population structure, the physiological condition, and the growth of R. cuneata collected from its distributional limits in Great Britain. Feeding rate of R. cuneata was quantified by conducting a reciprocal transfer experiment with a two-way factorial design on individuals obtained from the freshwater and saline extremes. R. cuneata density was almost 10-fold higher at its most saline distributional limit (213 individual m-2, 3.1‰) compared to its most freshwater limit (22 individuals m-2, 1.2‰). The impaired physiological condition (18.7% lower relative soft tissue mass and 26.4% lower shell mass) and the lack of juvenile individuals also suggests that the R. cuneata inhabiting the freshwater extreme may not be able to maintain a persistent population over the long term. Although R. cuneata at its freshwater extreme were under stress, the per capita impacts caused by these individuals were not weakened at the suboptimal conditions, evidenced by their elevated growth and over four times as high relative clearance rate (0.28 L-1 g-1 h-1) compared to those from the saline limit (0.06 L-1 g-1 h-1). This study demonstrates that under suboptimal conditions, the physiological responses of INNS may result in elevated per capita effects which may lead to unexpected or under-estimated impacts on recipient ecosystems.

Feeding and digestion of the marine isopod Idotea emarginata challenged by poor food quality and microplastics.

Ingestion of microplastics can impair nutrition of marine invertebrates. In a laboratory study, we tested whether microplastics affect ingestion rates and gastrointestinal enzyme activities in the marine isopod Idotea emarginata. Isopods were fed for eight days with one out of four different food formulations: natural food (the brown alga Fucus vesiculosus) or synthetic diet consisting of freeze-dried algal powder embedded in agarose, both, with or without microplastic particles (fluorescent polymethyl methacrylate, 10-100 µm) at a concentration of 40 items per mg of food. The isopods accepted both types of food but consumed significantly more (average 3.1-fold) of the agar based synthetic food. I. emarginata responded to the reduced content of digestible organic matter in the synthetic food by a compensatory adjustment of the ingestion rates. Addition of microplastics had no effect on ingestion rates in natural food whereas the feeding rates for synthetic food varied in response to microplastics. Similarly, activity patterns of digestive enzymes, particularly those of esterases, changed significantly in the treatment with synthetic food. Isopods fed with synthetic food alone showed elevated esterase activities in the gut while those isopods fed with synthetic food and microplastics showed elevated esterase activities in the midgut gland but not in the gut. Apparently, not the exposure to microplastic alone, but the combined effects of reduced nutrient availability and microplastic ingestion caused considerable biochemical reactions in the digestive organs of the isopods.

Effect of dietary energy restriction and subsequent compensatory feeding on testicular transcriptome in developing rams.

Nutritional intake and reproductive allocation are strongly associated and dietary energy restriction (ER) or surpluses can affect reproductive capacity. The objective of this study was to investigate the effect of energy levels on sheep testicular development. Three-month old Hu sheep were assigned to four groups, and fed diets containing different levels of energy (Control, maintenance energy; ER1, 85% maintenance energy; ER2, 70% maintenance energy; ER3, 55% maintenance energy). Two months later, half the sheep in each group were euthanized, whereas the remaining sheep were euthanized after a further 3 months feeding on a compensatory energy diet. The testicular weight and reproductive hormone levels of the Hu sheep were investigated. Differences in the testes of ER3 and control group sheep were investigated at the transcriptional level using high-throughput sequencing. The results showed that the testicular weights had decreased in the energy-restricted rams compared with the controls, and that the testosterone concentration in ER3 group rams was significantly lower than that in other compared groups (P < 0.05). After the period of compensatory feeding, however, ER3 sheep testicular weight and testosterone concentrations were similar to those of the control group sheep. In addition, the RNA sequencing results revealed that 81 genes were upregulated and 180 genes were downregulated in the ER3 group compared with the control group. Moreover, based on the enriched steroidogenesis, meiosis and kinases pathways, a number of candidate genes potentially involved in the regulation of testicular development or reproduction of Hu sheep, including CYP11A1, ALDH3B1, FDFT1, WNT2, PGR and INSR, were screened. Quantitative real-time polymerase chain reaction analysis results correlated well with the sequencing data. Taken together, this study provides a first insight into the development of the testis with dietary energy restriction in sheep and shows that these changes are associated with alterations in transcriptomic. The sheep testis mRNA database were extended in this study will provides novel candidate regulators for future genetic and molecular studies on sheep testicular development associated with energy restriction, which will contribute to improving the reproductive performance of sheep.

Transient effects following peak exposures towards pesticides - An explanation for the unresponsiveness of in situ measured functional variables.

Invertebrate-mediated leaf litter decomposition is frequently used to assess stress-related implications in stream ecosystem integrity. In situ measures such as the mass loss from leaf bags or the feeding of caged invertebrates deployed for days or weeks may, however, fail to detect transient effects due to recovery or compensatory mechanisms. We assessed the relevance of transient effects using the peak exposure towards an insecticide (i.e., etofenprox) as a model scenario at three levels of complexity. These were 1) the assessment of the decomposition realised by invertebrate communities in stream mesocosms over 21 days via leaf bags, 2) 7-days lasting in situ bioassays quantifying the leaf consumption of Gammarus fossarum, and 3) a laboratory experiment determining the daily feeding rate of the same species over 7 days. Etofenprox did not trigger a significantly altered decomposition by invertebrate communities during the leaf bag assay, while in situ bioassays detected a significant reduction in gammarids' feeding rate at the highest tested concentration. The laboratory bioassay suggests that observed mismatches might be explained by recovery and post-exposure compensation. As leaf-shredding invertebrates are likely in a vulnerable state following transient effects, biomonitoring for implications of peak exposures and other pulsed stress events must happen at an adequate temporal resolution.

Feeding Immunity: Physiological and Behavioral Responses to Infection and Resource Limitation.

Resources are a core currency of species interactions and ecology in general (e.g., think of food webs or competition). Within parasite-infected hosts, resources are divided among the competing demands of host immunity and growth as well as parasite reproduction and growth. Effects of resources on immune responses are increasingly understood at the cellular level (e.g., metabolic predictors of effector function), but there has been limited consideration of how these effects scale up to affect individual energetic regimes (e.g., allocation trade-offs), susceptibility to infection, and feeding behavior (e.g., responses to local resource quality and quantity). We experimentally rewilded laboratory mice (strain C57BL/6) in semi-natural enclosures to investigate the effects of dietary protein and gastrointestinal nematode (Trichuris muris) infection on individual-level immunity, activity, and behavior. The scale and realism of this field experiment, as well as the multiple physiological assays developed for laboratory mice, enabled us to detect costs, trade-offs, and potential compensatory mechanisms that mice employ to battle infection under different resource conditions. We found that mice on a low-protein diet spent more time feeding, which led to higher body fat stores (i.e., concentration of a satiety hormone, leptin) and altered metabolite profiles, but which did not fully compensate for the effects of poor nutrition on albumin or immune defenses. Specifically, immune defenses measured as interleukin 13 (IL13) (a primary cytokine coordinating defense against T. muris) and as T. muris-specific IgG1 titers were lower in mice on the low-protein diet. However, these reduced defenses did not result in higher worm counts in mice with poorer diets. The lab mice, living outside for the first time in thousands of generations, also consumed at least 26 wild plant species occurring in the enclosures, and DNA metabarcoding revealed that the consumption of different wild foods may be associated with differences in leptin concentrations. When individual foraging behavior was accounted for, worm infection significantly reduced rates of host weight gain. Housing laboratory mice in outdoor enclosures provided new insights into the resource costs of immune defense to helminth infection and how hosts modify their behavior to compensate for those costs.

Animal Guts as Ideal Chemical Reactors: Maximizing Absorption Rates.

I solved equations that describe coupled hydrolysis in and absorption from a continuously stirred tank reactor (CSTR), a plug flow reactor (PFR), and a batch reactor (BR) for the rate of ingestion and/or the throughput time that maximizes the rate of absorption (=gross rate of gain from digestion). Predictions are that foods requiring a single hydrolytic step (e.g., disaccharides) yield ingestion rates that vary inversely with the concentration of food substrate ingested, whereas foods that require multiple hydrolytic and absorptive reactions proceeding in parallel (e.g., proteins) yield maximal ingestion rates at intermediate substrate concentrations. Counterintuitively, then, animals acting to maximize their absorption rates should show compensatory ingestion (more rapid feeding on food of lower concentration), except for the lower range of diet quality for complex diets and except for animals that show purely linear (passive) uptake. At their respective maxima in absorption rates, the PFR and BR yield only modestly higher rates of gain than the CSTR but do so at substantially lower rates of ingestion. All three ideal reactors show milder than linear reduction in rate of absorption when throughput or holding time in the gut is increased (e.g., by scarcity or predation hazard); higher efficiency of hydrolysis and extraction offset lower intake. Hence adding feeding costs and hazards of predation is likely to slow ingestion rates and raise absorption efficiencies substantially over the cost-free optima found here.