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The handling and use of oxygen are central to physiological function of all pancrustaceans. Throughout the Pancrustacea, ventilation is controlled by a central oxygen-sensitive pattern generator. The ancestral condition was likely to achieve ventilation of the gills via leg-associated or mouth-associated muscles, but in insects and some air-breathing crustaceans, new muscles were recruited for this purpose, including intersegmental muscles likely used previously for posture and locomotion. Many aspects of the sensing of oxygen and the occurrence of responses to hypoxia (increased ventilation, depressed growth and metabolic rate, developmental changes that enhance the delivery of oxygen) appear common across most pancrustaceans, but there is tremendous variation across species. Some of this can be explained by habitat (e.g., ventilation of the internal medium occurs in terrestrial species and of the external medium in aquatic species; rearing under hypoxia induces tracheal proliferation in terrestrial insects and hemocyanin production in aquatic crustaceans); some plausibly by evolutionary origin of some responses to hypoxia within the Pancrustacea (the most basal arthropods may lack a ventilatory response to hypoxia); and some by the availability of environmental oxygen (animals adapted to survive hypoxia turn on the response to hypoxia at a lower PO₂). On average, crustaceans and insects have similar tolerances to prolonged anoxia, but species or life stages from habitats with a danger of being trapped in hypoxia can tolerate longer durations of anoxia. Lactate is the primary anaerobic end-product in crustaceans but some insects have evolved a more diverse array of anaerobic end-products, including ethanol, alanine, succinate, and acetate. Most clades of Pancrustacea are small and lack obvious respiratory structures. Gilled stem-pancrustaceans likely evolved in the Cambrian, and gills persist in large Ostracoda, Malacostraca, and Branchiopoda. Based on currently accepted phylogenies, invaginations of cuticle to form lungs or tracheae occurred independently multiple times across the Arthropoda and Pancrustacea in association with the evolution of terrestriality. However, the timing and number of such events in the evolution of tracheal systems remain controversial. Despite molecular phylogenies that place the origin of the hexapods before the appearance of land plants in the Ordovician, terrestrial fossils of Collembola, Archaeognatha, and Zygentoma in the Silurian and Devonian, and the lack of fossil evidence for older aquatic hexapods, suggest that the tracheated hexapods likely evolved from Remipedia-like ancestors on land.

Group size has profound effects on the organization of work. In the social insects, larger colony size is consistently associated with lower mass-specific energy use; similar hypometric relationships between group size and per-gram energy use may extend across other social taxa. The specific mechanisms driving social metabolic scaling vary among species, but evidence suggests that it can be associated with organizational changes in work (task) performance that allow more efficient energy use by larger groups. In social insect colonies, larger group size allows stronger individual specialization, greater diversity in task performance, and likely gives improved resilience to stochastic events. Larger colonies often also allocate a larger proportion of workers to maintenance and reserve rather than to foraging and brood care tasks, potentially reducing costs. For the few species examined, these organizational changes seem to be associated with lower mean but higher variance in movement rates, providing a concrete connection to metabolic use. Interestingly, colony group size is not generally associated with changes in the proportional number of colony workers resting versus doing work, but this may vary across social systems. Colonies with hypometric metabolic scaling tend to show constant or greater efficiency of brood production, consistent with efficiency rather than constraint-based scaling models. These patterns of work and energetics in social groups show distinct parallels with organismal scaling. Investigation into social metabolic scaling could contribute to identifying unifying scaling theories for the disparate fields of animal behavior, physiology, and human sociology.

Current paradigms generally assume that increased plant nitrogen (N) should enhance herbivore performance by relieving protein limitation, increasing herbivorous insect populations. We show, in contrast to this scenario, that host plant N enrichment and high-protein artificial diets decreased the size and viability of Oedaleus asiaticus, a dominant locust of north Asian grasslands. This locust preferred plants with low N content and artificial diets with low protein and high carbohydrate content. Plant N content was lowest and locust abundance highest in heavily livestock-grazed fields where soils were N-depleted, likely due to enhanced erosion. These results suggest that heavy livestock grazing and consequent steppe degradation in the Eurasian grassland promote outbreaks of this locust by reducing plant protein content.

Temperature is a key factor that affects the rates of growth and development in animals, which ultimately determine body size. Although not universal, a widely documented and poorly understood pattern is the inverse relationship between the temperature at which an ectothermic animal is reared and its body size (temperature size rule [TSR]). The proximate and ultimate mechanisms for the TSR remain unclear. To explore possible explanations for the TSR, we tested for correlations between the magnitude/direction of the TSR and latitude, temperature, elevation, habitat, availability of oxygen, capacity for flight, and taxonomic grouping in 98 species/populations of arthropods. The magnitude and direction of the TSR was not correlated with any of the macro-environmental variables we examined, supporting the generality of the TSR. However, body size affected the magnitude and direction of the TSR, with smaller arthropods more likely to demonstrate a classic TSR. Considerable variation among species exists in the TSR, suggesting either strong interactions with nutrition, or selection based on microclimatic or seasonal variation not captured in classic macro-environmental variables.

Managed honey bees have experienced high rates of colony loss recently, with pesticide exposure as a major cause. While pesticides can be lethal at high doses, lower doses can produce sublethal effects, which may substantially weaken colonies. Impaired learning performance is a behavioral sublethal effect, and is often present in bees exposed to insecticides. However, the effects of other pesticides (such as fungicides) on honey bee learning are understudied, as are the effects of pesticide formulations versus active ingredients. Here, we investigated the effects of acute exposure to the fungicide formulation Pristine (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin) on honey bee olfactory learning performance in the proboscis extension reflex (PER) assay. We also exposed a subset of bees to only the active ingredients to test which formulation component(s) were driving the learning effects. We found that the formulation produced negative effects on memory, but this effect was not present in bees fed only boscalid and pyraclostrobin. This suggests that the trade secret “other ingredients” in the formulation mediated the learning effects, either through exerting their own toxic effects or by increasing the toxicities of the active ingredients. These results show that pesticide co-formulants should not be assumed inert and should instead be included when assessing pesticide risks.

In almost all animals, physiologically low oxygen (hypoxia) during development slows growth and reduces adult body size. The developmental mechanisms that determine growth under hypoxic conditions are, however, poorly understood. Here we show that the growth and body size response to moderate hypoxia (10% O 2 ) in Drosophila melanogaster is systemically regulated via the steroid hormone ecdysone. Hypoxia increases level of circulating ecdysone and inhibition of ecdysone synthesis ameliorates the negative effect of low oxygen on growth. We also show that the effect of ecdysone on growth under hypoxia is through suppression of the insulin/IGF-signaling pathway, via increased expression of the insulin-binding protein Imp-L2 . These data indicate that growth suppression in hypoxic Drosophila larvae is accomplished by a systemic endocrine mechanism that overlaps with the mechanism that slows growth at low nutrition. This suggests the existence of growth-regulatory mechanisms that respond to general environmental perturbation rather than individual environmental factors.

The fitness consequences of cooperation can vary across an organism’s lifespan. For non-kin groups, especially, social advantages must balance intrinsic costs of cooperating with non-relatives. In this study, we asked how challenging life history stages can promote stable, long-term alliances among unrelated ant queens. We reared single- and multi-queen colonies of the primary polygynous harvester ant, Pogonomyrmex californicus , from founding through the first ten months of colony growth, when groups face high mortality risks. We found that colonies founded by multiple, unrelated queens experienced significant survival and growth advantages that outlasted the colony founding period. Multi-queen colonies experienced lower mortality than single-queen colonies, and queens in groups experienced lower mortality than solitary queens. Further, multi-queen colonies produced workers at a faster rate than did single-queen colonies, even while experiencing lower per-queen worker production costs. Additionally, we characterized ontogenetic changes in the organization of labor, and observed increasing and decreasing task performance diversity by workers and queens, respectively, as colonies grew. This dynamic task allocation likely reflects a response to the changing role of queens as they are increasingly able to delegate risky and costly tasks to an expanding workforce. Faster worker production in multi-queen colonies may beneficially accelerate this behavioral transition from a vulnerable parent–offspring group to a stable, growing colony. These combined benefits of cooperation may facilitate the retention of multiple unrelated queens in mature colonies despite direct fitness costs, providing insight into the evolutionary drivers of stable associations between unrelated individuals.

Organisms require dietary macronutrients in specific ratios to maximize performance, and variation in macronutrient requirements plays a central role in niche determination. Although it is well recognized that development and body size can have strong and predictable effects on many aspects of organismal function, we lack a predictive understanding of ontogenetic or scaling effects on macronutrient intake. We determined protein and carbohydrate intake throughout development on lab populations of locusts and compared to late instars of field populations. Self-selected protein:carbohydrate targets declined dramatically through ontogeny, due primarily to declines in mass-specific protein consumption rates which were highly correlated with declines in specific growth rates. Lab results for protein consumption rates partly matched results from field-collected locusts. However, field locusts consumed nearly double the carbohydrate, likely due to higher activity and metabolic rates. Combining our results with the available data for animals, both across species and during ontogeny, protein consumption scaled predictably and hypometrically, demonstrating a new scaling rule key for understanding nutritional ecology.