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Browsing herbivores must consider food digestibility while balancing the intake of multiple nutrients (i.e., protein and energy) simultaneously. Nutritional Geometry (NG) is a framework that is used to assess how nutrients interact to impact animal feeding behavior and body condition. Here, we use NG combined with detailed digestibility trials to evaluate how snowshoe hares (Lepus americanus), a common boreal browser that experiences 10‐year population cycles, balance energy and protein. We conducted 65 no‐choice and 15 multi‐choice feeding trials on 17 hares in Kluane, Yukon (Canada) during the winters of 2022 and 2023. We tested four diets ranging from the low protein (5.6%) and high fiber content of hare winter food (twigs) to the high protein (16.7%) and low fiber content of rabbit chow. We measured daily intake per kg0.75 per day in multi‐choice trials and daily intake, weight change, and digestibility in no‐choice trials. We analyzed the effect of diet treatment on each response and the effect of protein and energy intake, in both crude and digestible terms, on feeding rates and weight change. In multi‐choice trials, hares chose a diet balanced in energy and protein, but with a protein content above that in twigs. On single diets, hares were fed to meet a minimum daily digestible energy intake of approximately 1000 kJ/kg0.75/day, regardless of protein content, after which digestible protein influenced weight change (p = 0.02). We found that hares could maintain their weight after they acquired 6 g of digestible protein per kg0.75/day. Our results suggest that snowshoe hares choose to consume food items on the basis of the interaction between energy and protein, and these choices influence weight change. Our work supports previous hypotheses that declines in twig quality at peak hare densities could contribute to the subsequent increase in over‐winter weight loss that occurs during the population crash. Here, we use nutritional geometry and classical feeding trial methods to evaluate how snowshoe hares balance energy and protein. Our results suggest that snowshoe hares choose to consume food items on the basis of the interaction between energy and protein, and these choices influence weight change. Our work supports previous hypotheses that declines in twig quality at peak hare densities could contribute to the subsequent increase in over‐winter weight loss that occurs during the population crash.

In 2012, a controversial study on the long-term toxicity of a Roundup herbicide and the glyphosate-tolerant genetically modified (GM) maize NK603 was published. The EC-funded G-TwYST research consortium tested the potential subchronic and chronic toxicity as well as the carcinogenicity of the glyphosate-resistant genetically modified maize NK603 by performing two 90-day feeding trials, one with GM maize inclusion rates of 11 and 33% and one with inclusion rates of up to 50%, as well as a 2-year feeding trial with inclusion rates of 11 and 33% in male and female Wistar Han RCC rats by taking into account OECD Guidelines for the testing of chemicals and EFSA recommendations on the safety testing of whole-food/feed in laboratory animals. In all three trials, the NK603 maize, untreated and treated once with Roundup during its cultivation, and the conventional counterpart were tested. Differences between each test group and the control group were evaluated. Equivalence was assessed by comparing the observed difference to differences between non-GM reference groups in previous studies. In case of significant differences, whether the effects were dose-related and/or accompanied by changes in related parameters including histopathological findings was evaluated. It is concluded that no adverse effects related to the feeding of the NK603 maize cultivated with or without Roundup for up to 2 years were observed. Based on the outcome of the subchronic and combined chronic toxicity/carcinogenicity studies, recommendations on the scientific justification and added value of long-term feeding trials in the GM plant risk assessment process are presented.

Conservation biological control efforts depend on accurately estimating predator roles in crop fields, and knowledge of plant resources generalist predators utilize in agricultural landscapes. Generalist predators move among habitats to feed on insect prey and some predators feed on plants for non‐prey nutrients. Studying predation with molecular gut content analysis (MGCA), provides estimates of within field frequencies of predation on target pests and alternative prey. However, prey DNA takes time to move through the predator digestive system, so a portion of the observed predation likely occurs in adjacent crops or semi‐natural habitats. Therefore, we tested a strategy to estimate recent secondary feeding to help trace predation back to the source habitat. We selected the diamondback moth and three common predators with different mouthparts: Coccinella septempunctata, Geocoris punctipes, and Pardosa spiders, as model organisms for these proof‐of‐concept experiments. We estimated post‐feeding primary and secondary plant DNA detection time and compared it between these three predators using previously designed Lepidoptera primers and newly designed Brassica‐specific primers. Our results indicate secondary plant feeding detection largely depends on predator mouthparts. While secondary collard DNA detectability half‐life was 5.5 h and remained detectable for up to 30 h for the chewing predator, C. septempunctata, only 4% and 8.3% of G. punctipes and Pardosa spp. individuals, respectively, tested positive for collard DNA. However, more studies are required to confirm this mouthpart‐specific post‐feeding plant DNA detection time. Our feeding trials confirmed the possibility of primary and secondary plant feeding detection for chewing predators. Hence, when crops are not flowering (or anthesis), secondary plant feeding detection can be used to trace chewing predators to source habitats where they consumed sessile prey (e.g., nymphs and sessile adults). Such multitrophic linkage knowledge could unravel the landscape‐wise contribution of predators to pest control services. Our study indicates the possibility of secondary plant DNA detection in generalist predators' diets with chewing mouthparts and, to a lesser extent, in spiders. Our finding has implications for future molecular gut content analysis in agricultural fields and environments, tracking prey feeding to source habitats, and potentially speculating the direct or indirect source of plant feeding in arthropod natural enemies and vertebrate diet.

Understanding between-individual variability in energy acquisition is essential for elucidating many ecological processes in wild fish populations and for enhancing the efficiency of aquaculture production. This study explores whether individual variations in feed ingestion rates among group-reared fish can arise from intrinsic fish-specific, size-independent factors. Specifically, we quantify the residual variability in ingestion rate (i.e., the variability beyond body size effects and extrinsic influences) to assess the role of context-independent, stable, intrinsic behavioural differences that may lead to feeding hierarchies. We monitored the individual feeding behaviour of 48 European seabass adult females (Dicentrarchus labrax) externally tagged reared in sea cages (6 cages housing 8 fish each) under three feeding levels (two cages per level) over four months. Across 8 repeated feeding trials per cage, fish were offered feed pellets one at a time using an automated feeder, and their individual pellet consumption were video recorded. Using a Bayesian statistical model, we evaluated the fish-specific probability of pellet consumption as a function of body size, temperature, anthropogenic stress and feeding level, while accounting for variation across individuals and feeding trials. Our results showed: i) a substantial and consistent between-individual variability in ingestion rates across feeding trials, and ii) a relevant negative effect of anthropogenic stress on feeding activity. Notably, individual-specific effects, independent of body size and external variables, accounted for over 70% of the variance in ingestion rate, suggesting that intrinsic and stable behavioural differences, indicative of fish behavioural types, may play a central role in shaping feeding hierarchies.

To determine the effect of oat β‑glucan (OBG) on acute glucose and insulin responses and identify significant effect modifiers we searched the MEDLINE, EMBASE, and Cochrane databases through October 27, 2020 for acute, crossover, controlled feeding trials investigating the effect of adding OBG (concentrate or oat-bran) to carbohydrate-containing test-meals compared to comparable or different carbohydrate-matched control-meals in humans regardless of health status. The primary outcome was glucose incremental area-under-the-curve (iAUC). Secondary outcomes were insulin iAUC, and glucose and insulin incremental peak-rise (iPeak). Two reviewers extracted the data and assessed risk-of-bias and certainty-of-evidence (GRADE). Data were pooled using generic inverse-variance with random-effects model and expressed as ratio-of-means with [95% CIs]. We included 103 trial comparisons (N = 538). OBG reduced glucose iAUC and iPeak by 23% (0.77 [0.74, 0.81]) and 28% (0.72 [0.64, 0.76]) and insulin by 22% (0.78 [0.72, 0.85]) and 24% (0.76 [0.65, 0.88]), respectively. Dose, molecular-weight, and comparator were significant effect modifiers of glucose iAUC and iPeak. Significant linear dose-response relationships were observed for all outcomes. OBG molecular-weight >300 kg/mol significantly reduced glucose iAUC and iPeak, whereas molecular-weight <300 kg/mol did not. Reductions in glucose iAUC (27 vs 20%, p = 0.03) and iPeak (39 vs 25%, p < 0.01) were significantly larger with different vs comparable control-meals. Outcomes were similar in participants with and without diabetes. All outcomes had high certainty-of-evidence. In conclusion, current evidence indicates that adding OBG to carbohydrate-containing meals reduces glycaemic and insulinaemic responses. However, the magnitude of glucose reduction depends on OBG dose, molecular-weight, and the comparator.

Herbivorous and detritivorous fishes interact closely with the epilithic algal matrix (EAM) on coral reefs. While sediment and organic detrital loads within the EAM might influence this interaction, the responses of functionally distinct fishes to changing sediment and organic loads have not been investigated. Aquarium based feeding trials were performed to assess how different sediment and organic loads affected feeding by the highly abundant surgeonfishes, Ctenochaetus striatus, a detritivore, and Acanthurus nigrofuscus, a herbivore. C. striatus were highly sensitive to even small increases in sediment loads (of just 75 g m-2), displaying a significant decline in feeding rates as sediment loads increased. Although C. striatus is a specialised detritivore, changing organic loads had no effect and suggests that selection of feeding surfaces is primarily mediated by total sediment loads rather than organic loads. By contrast, A. nigrofuscus displayed no changes to its feeding behaviour regardless of sediment or organic load. These findings highlight the complex, species-specific way that sediments may mediate key ecological processes on coral reefs.

One of the least understood trophic pathways on coral reefs is the linkage between highly productive cryptic motile invertebrates (herein: cryptofauna) and the predatory vertebrates that underpin reef fisheries. As cryptofauna are difficult to observe and quantify, particularly in coral rubble where they proliferate, the diets of invertivores that forage in rubble have largely been determined through relative gut content analyses. Without congruent quantification of prey diversity, biomass, and rates of predation specific to rubble, it remains challenging to develop models of productivity and energy transfer. We calculated bite rates of six wrasses (Labridae) and a goatfish (Mullidae) commonly found foraging in rubble, using in situ videography on a coral reef in Palau, Western Micronesia. Consumption rates (i.e. individuals consumed) and prey preferences were determined using tank-based feeding experiments, where individual fish were presented with a diverse rubble community characterised before and after 2 h feeding trials. The motile cryptofauna community and invertivore diet consisted predominantly of Arthropoda (83% and > 58%, respectively), with calanoid copepods and mysids positively selected and harpacticoids, decapods and ostracods negatively selected. The interspecific mean (± standard error) rate of consumption was 3.5 ± 0.2 ind. min −1 from rubble, estimated to equal 9.5 ± 0.9 mg min −1 of invertebrate biomass consumed per fish, with biased uptake of small fauna. Bite and consumption rates varied among species with the greatest efficiency in biomass uptake evident in Halichoeres melanurus. This study provides a first attempt at characterising diverse cryptofauna communities pre- and post-trial to identify feeding rates and preferences of coral reef invertivores from the rubble benthos, and highlights the importance of addressing the bioavailability of lower trophic entities in energy pathways.

Stable isotope mixing models (SIMMs) are an important tool used to study species’ trophic ecology. These models are dependent on, and sensitive to, the choice of trophic discrimination factors (TDF) representing the offset in stable isotope delta values between a consumer and their food source when they are at equilibrium. Ideally, controlled feeding trials should be conducted to determine the appropriate TDF for each consumer, tissue type, food source, and isotope combination used in a study. In reality however, this is often not feasible nor practical. In the absence of species-specific information, many researchers either default to an average TDF value for the major taxonomic group of their consumer, or they choose the nearest phylogenetic neighbour for which a TDF is available. Here, we present the SIDER package for R, which uses a phylogenetic regression model based on a compiled dataset to impute (estimate) a TDF of a consumer. We apply information on the tissue type and feeding ecology of the consumer, all of which are known to affect TDFs, using Bayesian inference. Presently, our approach can estimate TDFs for two commonly used isotopes (nitrogen and carbon), for species of mammals and birds with or without previous TDF information. The estimated posterior probability provides both a mean and variance, reflecting the uncertainty of the estimate, and can be subsequently used in the current suite of SIMM software. SIDER allows users to place a greater degree of confidence on their choice of TDF and its associated uncertainty, thereby leading to more robust predictions about trophic relationships in cases where study-specific data from feeding trials is unavailable. The underlying database can be updated readily to incorporate more stable isotope tracers, replicates and taxonomic groups to further increase the confidence in dietary estimates from stable isotope mixing models, as this information becomes available.

Molecular gut-content analysis has revolutionized the study of food webs and feeding inter- actions, allowing the detection of prey DNA within the gut of many organisms. However, suc- cessful prey detection is a challenging procedure in which many factors affect every step, starting from the DNA extraction process. Spiders are liquid feeders with branched gut diver- ticula extending into their legs and throughout the prosoma, thus digestion takes places in different parts of the body and simple gut dissection is not possible. In this study, we investi- gated differences in prey detectability in DNA extracts from different parts of the spider ́s body: legs, prosoma and opisthosoma, using prey-specific PCR and metabarcoding approaches. We performed feeding trials with the woodlouse hunter spider Dysdera ver- neaui Simon, 1883 (Dysderidae) to estimate the time at which prey DNA is detectable within the predator after feeding. Although we found that all parts of the spider body are suitable for gut-content analysis when using prey-specific PCR approach, results based on metabar- coding suggested the opisthosoma is optimal for detection of predation in spiders because it contained the highest concentration of prey DNA for longer post feeding periods. Other spi- ders may show different results compared to D. verneaui, but given similarities in the physi- ology and digestion in different families, it is reasonable to assume this to be common across species and this approach having broad utility across spiders.

Crown-of-thorns starfish (CoTS) are a pervasive coral predator prone to population outbreaks that have damaged coral reefs across Australia and the wider Indo-Pacific. CoTS population control through predation has been suggested as a primary mechanism that suppresses their outbreaks. However, the nature and rates of predation on CoTS are poorly resolved, especially for early life-history stages where they are expected to be most vulnerable. Here, we provide results from the first investigation of predators of CoTS during their rubble-dwelling, herbivorous, juvenile phase. We assessed the capacity of 104 common species of the rubble cryptofauna found across Heron Reef, Great Barrier Reef, Australia, to consume early-stage juvenile CoTS (0.8–3.8 mm) using controlled feeding experiments with laboratory-raised juveniles. We identified 26 novel CoTS predators, but only 10 species that regularly consumed juvenile CoTS in their entirety. Most cases of predation resulted in severed bodies and missing arms (i.e. sublethal predation) but not total consumption. We highlight one crustacean predator, Schizophrys aspera, the red decorator crab, which consumed whole juvenile CoTS in 89% of feeding trials and in excess of 5 CoTS d−1 in natural rubble mesocosms with alternative prey. This work emphasises the importance of predators at the critical juvenile stage that may control the build-up of CoTS populations prior to being detectable as an outbreak population.