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Nutrition is vital to health, but while the link between diet and body nutritional composition is well explored in humans and other vertebrates, this information is not well understood in insects, despite the vital roles they play in ecosystems, and their increasing use as experimental models. Here we used Nutritional Geometry to explore the rapid physiological response to ingested nutrients in the haemolymph nutritional profile of Spodoptera littoralis caterpillars. We ask whether blood nutrients are maintained homeostatically in the face of variable nutritional intake, or if regulation is more flexible for some nutrients than others (allostasis), which allows animals to adapt to stress by responding in a way that prioritises efficiency of responses in the face of trade‐offs. Caterpillars were placed on 1 of 20 diets, systematically varying in their nutrient ratios (protein: carbohydrate) and density (calorie content), and their consumption was measured. After 48 h, caterpillars were bled, and the macronutrient (protein, carbohydrates and lipids) and nutrient metabolite (amino acids and simple sugars) content of the haemolymph was measured. Proteins comprised 93% of the haemolymph macronutrient pool on average and their concentration increased with protein eaten. The amino acid (AA) pool was dominated by five AAs, and the total pool increased with total nutrient intake. However, the ratio of essential to non‐essential AAs increased as the proportion of protein consumed increased. Carbohydrates were tightly controlled, increasing only on the most extreme carbohydrate intakes. Simple sugars were dominated by glucose and trehalose, and overall, the simple sugar pool showed high levels of homeostasis. Rather than strict homeostasis of blood nutritional properties, an allostatic model seemed to be a better fit for blood nutrient regulation in this generalist herbivore. This flexibility in response to the nutritional composition of the diet may, in part, explain how this species has evolved to extreme dietary generalism and may play a role in its worldwide pest status. Given the range of fitness‐related processes affected by the haemolymph, future studies should examine the physiological impacts of blood nutrient variation on reproduction, growth and response to infection and the trade‐offs between them. [ABSTRACT FROM AUTHOR]

Simple Summary: Anticoagulant rodenticides are commonly used as a method of rodent population control. Unfortunately, many non-target species are exposed to rodenticides. The route by which non-target animals are poisoned is not always clear, which can hinder conservation efforts. It has been suggested that insectivorous species may be exposed to rodenticides via the consumption of contaminated insect prey. This study examined whether rodenticide baits mixed with the biomarker rhodamine B can be used to track invertebrate consumption of rodenticide baits in a natural environment, and, in doing so, we assessed whether insects could be a source of rodenticide poisoning in insectivores. The rhodamine B baits created an observable response; molluscs were the most frequent consumers of bait. Maximum temperature, distance from baits, the addition of copper tape to boxes, and proximity to buildings were all found to affect their rate of uptake. Other invertebrates rarely showed signs of uptake. This has provided valuable insights into the mechanisms by which insectivores experience rodenticide poisoning, which is necessary in developing effective mitigation measures to aid conservation efforts. We suggest that further investigation into using mollusc repellents around bait boxes should be considered. Non-target species are commonly exposed to anticoagulant rodenticides worldwide, which may pose a key threat to declining species. However, the main pathway of exposure is usually unknown, potentially hindering conservation efforts. This study aimed to examine whether baits mixed with the biomarker rhodamine B can be used to track invertebrate consumption of rodenticides in a field environment, using this to observe whether invertebrate prey are a potential vector for anticoagulant rodenticides in the diet of insectivores such as the European hedgehog (Erinaceus europaeus). Rhodamine B baits were found to create an observable response. Uptake was negligible in captured insects; however, 20.7% of slugs and 18.4% of snails captured showed uptake of bait. Maximum temperature, distance from bait, proximity to buildings, and the addition of copper tape to bait boxes all influenced the rate of bait uptake in molluscs. Based on these data, it seems likely that molluscs could be a source of rodenticide poisoning in insectivores. This research demonstrates which prey may pose exposure risks to insectivores and likely environmental factors, knowledge of which can guide effective mitigation measures. We suggest that further investigation into using mollusc repellents around bait boxes should be considered. [ABSTRACT FROM AUTHOR]

Aim: Body size explains most of the variation in fitness within animal populations and is therefore under constant selection from ecological and reproductive pressures, which often promote its evolution in sex‐specific directions, leading to sexual size dimorphism (SSD). Several hypotheses have been proposed to explain the vast diversity of SSD across species. These hypotheses emphasize: (a) the mate competition benefits to larger male size (sexual selection); (b) the benefits of larger female size for fecundity (fecundity selection); (c) the simultaneous benefits of niche divergence for males and females to reduce intersexual competition for ecological resources (natural selection); and (d) the underlying impact of geographical variation in climatic pressures expected to shape large‐scale patterns of SSD in synergy with the above selection pressures (e.g., intensification of fecundity selection as breeding seasons shorten). Based on a new, global‐scale amphibian dataset, we address the shortage of large‐scale, integrative tests of these four hypotheses. Location: Global. Time period: Extant. Major taxa studied: Class Amphibia. Methods: Using a > 3,500 species dataset spanning body size, ecological, life‐history, geographical and climatic data, we performed phylogenetic linear models to address the sexual, fecundity, ecological and climatic hypotheses of SSD. Results: Evolution of SSD is discordant between anurans and salamanders. Anuran SSD is shaped by climate (male‐biased SSD increases with temperature seasonality) and by nesting site. In salamanders, SSD converges across species that occupy the same types of microhabitats ("ecodimorphs"), whereas reproductive or climatic pressures have no effects on their SSD. These contrasts are associated with latitudinal gradients of SSD in anurans, but not in salamanders. Main conclusions: Amphibian SSD is driven by ecological and climatic pressures, whereas no roles for sexual or fecundity selection were detected. We show that macroevolutionary processes determined by different forms of selection lead to latitudinal patterns of trait diversity, and the lack of them. [ABSTRACT FROM AUTHOR]

Immunity and nutrition are two essential modulators of individual fitness. However, while the implications of immune function and nutrition on an individual's lifespan and reproduction are well established, the interplay between feeding behaviour, infection and immune function remains poorly understood. Asking how ecological and physiological factors affect immune responses and resistance to infections is a central theme of eco‐immunology.In this study, we used the fruit fly, Drosophila melanogaster, to investigate how infection through septic injury modulates nutritional intake and how macronutrient balance affects survival to infection by the pathogenic Gram‐positive bacterium Micrococcus luteus.Our results show that infected flies maintain carbohydrate intake, but reduce protein intake, thereby shifting from a protein‐to‐carbohydrate (P:C) ratio of ~1:4 to ~1:10 relative to non‐infected and sham‐infected flies. Strikingly, the proportion of flies dying after M. luteus infection was significantly lower when flies were fed a low‐P high‐C diet, revealing that flies shift their macronutrient intake as means of nutritional self‐medication against bacterial infection.These results are likely due to the effects of the macronutrient balance on the regulation of the constitutive expression of innate immune genes, as a low‐P high‐C diet was linked to an upregulation in the expression of key antimicrobial peptides.Together, our results reveal the intricate relationship between macronutrient intake and resistance to infection and integrate the molecular cross‐talk between metabolic and immune pathways into the framework of nutritional immunology. [ABSTRACT FROM AUTHOR]

Herbivores and omnivores, faced with a nutritionally complex diet, have evolved the capacity to balance the intake of specific nutrients. Recent studies have found that carnivores also have this capacity, despite their more nutritionally homogeneous diet. However, unlike herbivores and omnivores who prioritize protein intake when restricted to imbalanced foods, carnivores instead show much stricter regulation of fat intake. These choices to over- or under-consume nutrients when the intake target cannot be achieved are known as rules of compromise. To date, studies examining these rules have all been carried out at a single life stage, and it is unclear if these rules regarding the prioritization of nutrients are fixed or labile. We address this question with a carnivorous beetle, Nicrophorus vespilloides. We use a combination of dietary restriction and choice tests to determine the intake target and rules of compromise in reproductively mature beetles and in newly emerged adults undergoing a period of maturation feeding. We show that, despite having very similar intake targets, the rules of compromise differ between the 2 life stages. Although mature adults follow the typical carnivore rule of fat prioritization, immature adults behave more like omnivores, showing strict regulation of protein intake, resulting in obesity when restricted to protein-poor diets. These alternate rules suggest different mechanisms or capacities to cope with excess protein across these life stages. Examining how intake targets and rules of compromise change across life stages could be a valuable approach for our understanding of how animals will fare under rapidly changing environmental conditions. [ABSTRACT FROM AUTHOR]