Explore the vast range of titles available.

Behavioral flexibility for appropriate action selection is an advantage when animals are faced with decisions that will determine their survival or death. In order to arrive at the right decision, animals evaluate information from their external environment, internal state, and past experiences. How these different signals are integrated and modulated in the brain, and how context- and state-dependent behavioral decisions are controlled are poorly understood questions. Studying the molecules that help convey and integrate such information in neural circuits is an important way to approach these questions. Many years of work in different model organisms have shown that dopamine is a critical neuromodulator for (reward based) associative learning. However, recent findings in vertebrates and invertebrates have demonstrated the complexity and heterogeneity of dopaminergic neuron populations and their functional implications in many adaptive behaviors important for survival. For example, dopaminergic neurons can integrate external sensory information, internal and behavioral states, and learned experience in the decision making circuitry. Several recent advances in methodologies and the availability of a synaptic level connectome of the whole-brain circuitry of Drosophila melanogaster make the fly an attractive system to study the roles of dopamine in decision making and state-dependent behavior. In particular, a learning and memory center—the mushroom body—is richly innervated by dopaminergic neurons that enable it to integrate multi-modal information according to state and context, and to modulate decision-making and behavior.

Many populations of consumers consist of relatively specialized individuals that eat only a subset of the foods consumed by the population at large. Although the ecological significance of individual-level diet variation is recognized, such variation is difficult to document, and its underlying mechanisms are poorly understood. Optimal foraging theory provides a useful framework for predicting how individuals might select different diets, positing that animals balance the “opportunity cost” of stopping to eat an available food item against the cost of searching for something more nutritious; diet composition should be contingent on the distribution of food, and individual foragers should be more selective when they have greater energy reserves to invest in searching for high-quality foods. We tested these predicted mechanisms of individual niche differentiation by quantifying environmental (resource heterogeneity) and organismal (nutritional condition) determinants of diet in a widespread browsing antelope (bushbuck, Tragelaphus sylvaticus) in an African floodplain-savanna ecosystem. We quantified individuals’ realized dietary niches (taxonomic richness and composition) using DNA metabarcoding of fecal samples collected repeatedly from 15 GPS-collared animals (range 6–14 samples per individual, median 12). Bushbuck diets were structured by spatial heterogeneity and constrained by individual condition. We observed significant individual-level partitioning of food plants by bushbuck both within and between two adjacent habitat types (floodplain and woodland). Individuals with home ranges that were closer together and/or had similar vegetation structure (measured using LiDAR) ate more similar diets, supporting the prediction that heterogeneous resource distribution promotes individual differentiation. Individuals in good nutritional condition had significantly narrower diets (fewer plant taxa), searched their home ranges more intensively (intensity-of-use index), and had higher-quality diets prediction that animals with greater endogenous reserves have narrower realized niches because they can invest more time in searching for nutritious foods. Our results support predictions from optimal foraging theory about the energetic basis of individual-level dietary variation and provide a potentially generalizable framework for understanding how individuals’ realized niche width is governed by animal behavior and physiology in heterogeneous landscapes.

Behavioral expression can vary both within‐ (i.e., plasticity) and among‐individuals (i.e., animal personality), and understanding the causes and consequences of variation at each of these levels is a major area of investigation in contemporary behavioral ecology. Here, we studied sources of variation in both plasticity and personality in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius) in two consecutive years. We found that peregrines adjusted their nest defense in response to nesting stage and year, revealing plastic, state‐dependent, adjustment of nest defense. At the same time, nest defense behavior was repeatable in peregrine falcons both within and between years. We tested if fluctuating selection on behavioral types (i.e., individuals average phenotypic expression) and/or assortative mating acted to maintain long‐term among‐individual differences in nest defense behavior. We found that selection on female nest defense differed across years; being positive in 1 year and negative in the other. We also found support for assortative mating in the first year, but disassortative mating in the second. We propose two potential explanations for the observed year‐specific patterns of nonrandom mating: (1) year‐specific plastic adjustment of nest defense and/or (2) changes in the age‐structure of the breeding population. These posthoc explanations are speculative, and require further study. Unfortunately, we could not evaluate this directly with the available data, and future studies are needed with more than 2 years of data on nest‐defense and fitness outcomes, and with a larger number of marked individuals, to properly evaluate these potential explanations. We studied nest defense behavior in peregrine falcons in two successive breeding seasons to evaluate (1) the extent of repeatable variation in nest defense, and (2) evaluate alternative mechanisms that could maintain this variation. We found that nest defense was repeatable both within‐ and across years, and that patterns of (dis‐)assortative mating and selection on nest defense differed across the two study years. We suggest that changing selection on nest defense leads to plastic adjustment of nest defense behavior that generates changing patterns of assortative mating.

Summary Animals frequently exhibit consistent among‐individual differences in behavioural and physiological traits that are inherently flexible. Why should individuals differ consistently in their expression of labile traits? Recently, positive feedbacks between state and behaviour have been proposed as a possible explanation for the maintenance of consistent among‐individual differences in both state and behaviour. If state affects behaviour, and behaviour reciprocally affects state, then differences in either state or behaviour that arise among individuals even by chance could be maintained over extended periods of time. We tested for positive feedbacks experimentally using wild‐caught red knots (Calidris canutus islandica). In the wild, knots exhibit consistent among‐individual differences in digestive physiology (the mass of the muscular part of the stomach, the gizzard) and foraging behaviour (diet), two inherently labile traits. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentally manipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials. The effect of gizzard mass on diet choice, though in the predicted direction, was not statistically significant. Individuals exhibited consistent differences in foraging behaviour of unknown origin independent of current gizzard mass, as well as large residual unexplained variance in foraging behaviour. These two sources of variation in foraging behaviour overruled the gizzard mass‐dependent foraging behaviour and hence eroded the treatment‐related differences in gizzard mass. We conclude that positive feedbacks between diet choice and gizzard mass play at best a limited role in maintaining among‐individual variation in gizzard mass in red knots. Furthermore, we suggest that many models of state–behaviour feedbacks likely overestimate their potential importance in maintaining long‐term among‐individual variation in labile traits because most models of state–behaviour feedbacks fail to account for the effects of additional factors that may act to disrupt the feedback loops. The among‐individual differences in diet choice observed during solitary foraging trials eroded the consistent among‐individual differences in gizzard mass observed following periods of staple diet treatments in which knots foraged in social groups. Social foraging interactions may play an important role determining the expression of foraging behaviours such as intake rate that in turn influence gizzard mass. Further studies are needed to experimentally test the role of social interactions as a mechanism generating consistent among‐individual differences in foraging behaviours and gizzard mass. A lay summary is available for this article. Lay Summary

Daphnia and other zooplankton often harbour substantial intraspecific diversity in migration behaviour. One example is partial diel vertical migration (DVM), wherein a portion of the population migrates vertically at night while another portion remains deep in the water column. This behaviour is widespread among aquatic invertebrates and can strongly influence interspecific competition. However, the mechanisms maintaining partial DVM in zooplankton are poorly understood. Here, we take an observational approach to identify the likely mechanisms maintaining partial DVM in a natural population of Daphnia pulicaria. The Daphnia at our study site show intraspecific diversity in body hemoglobin (Hb) concentration. This variation serves as a marker for differential use of a deep low-oxygen layer, which allows us to concurrently examine the relationships between individual state, genotype, and migration behaviour within the population. We found that migration behaviour within Hb-rich and Hb-poor Daphnia was not related to individual size. Furthermore, Hb-rich and Hb-poor individuals were present within all commonly found genotypes. Thus, partial DVM in the population is neither a state-dependent behaviour based on size, nor the result of a genetic polymorphism. Characterizing partial DVM provides a more precise picture of aquatic ecosystems which can strongly influence estimates of population growth and trophic interactions.

Life‐history trade‐offs are considered a major driving force in the emergence of consistent behavioural differences (personality variation); but empirical tests are scarce. We investigated links between a personality trait (escape response), life‐history and state variables (growth rate, size and age at first reproduction, age‐dependent reproductive rates, lifetime reproductive success, life span) in red and green colour morphs of clonal pea aphids, Acyrthosiphon pisum. Escape response (dropping/non‐dropping off a plant upon a predatory attack) was measured repeatedly to classify individuals as consistent droppers, consistent nondroppers or inconsistents. Red morphs experienced stronger trade‐offs between early reproduction and life span than green morphs; and red consistent (non)droppers had highest lifetime reproductive success. Red droppers followed a risk‐averse life‐history strategy (high late reproduction), red nondroppers a risk‐prone strategy (high early reproduction), while reproductive rates were equivalent for all green behavioural types and red inconsistents. This suggests that red morphs suffer the highest costs of dropping (they are most conspicuous to predators), which ‘equivalates’ fitness payoffs to both risk‐takers (red non‐droppers) and risk‐averse red droppers. The strong trade‐off also means that committing to a particular lifestyle (being consistent) maximises fitness. Our study suggests that life‐history trade‐offs likely mediate personality variation but effects might depend on interactions with other organismal characteristics (here: colour morph).

Understanding and predicting catalytic activity in transition‐metal oxides remains challenging due to the multiscale interplay between geometric and electronic structure. Here, we propose a Hierarchical Embedded Sphere Model (HESM) integrating density functional theory (DFT) with interpretable machine learning (IML) to establish a generalizable descriptor framework for oxide electrocatalysis. By analyzing transition metal‐doped anatase MO2 (101) surfaces, HESM disentangles catalytic activity into three hierarchical contributions: Global electronic structure (G‐class), atomic‐site intrinsic properties (A‐class), and local coordination effect (L‐class). The combined effect of these three classes leads to the emergence of two catalytic activation paradigms: Rh@MO2 optimizes activity via dopant‐induced electronic modulation (ηTD = 0.29–0.36 V), while Fe@ZrO2 enhances performance (ηTD = 0.49 V) by host‐site coordination field tuning. The hierarchical framework explains the competitive adsorption of OH* across doped/host sites, reconciles the well‐known V‐shaped activity trends with site‐dependent deviations, and SHapley Additive exPlanation (SHAP) analysis identifies G‐class as a critical feature that governs the model's prediction. This work demonstrates that HESM bridges adsorption energetics with multiscale geometric‐electronic couplings, offering a generalizable methodology for descriptor discovery and catalyst design in complex systems. Hierarchical Embedded Sphere Model combines DFT and interpretable machine learning to decode catalytic activity on TM‐doped MO2. It disentangles global electronic, active‐site, and local coordination effects, revealing two activation mechanisms: dopant‐driven (Rh@MO2) and coordination‐mediated (Fe@ZrO2). This model unifies OH* competition and V‐shaped adsorption trends. SHAP analysis identifies G‐class as the dominant descriptor for oxide electrocatalysis.

Glucocorticoids (GC) and triiodothyronine (T3) are two endocrine markers commonly used to quantify resource limitation, yet the relationships between these markers and the energetic state of animals has been studied primarily in small-bodied species in captivity. Free-ranging animals, however, adjust energy intake in accordance with their energy reserves, a behavior known as state-dependent foraging. Further, links between life-history strategies and metabolic allometries cause energy intake and energy reserves to be more strongly coupled in small animals relative to large animals. Because GC and T3 may reflect energy intake or energy reserves, state-dependent foraging and body size may cause endocrine–energy relationships to vary among taxa and environments. To extend the utility of endocrine markers to large-bodied, free-ranging animals, we evaluated how state-dependent foraging, energy reserves, and energy intake influenced fecal GC and fecal T3 concentrations in free-ranging moose (Alces alces). Compared with individuals possessing abundant energy reserves, individuals with few energy reserves had higher energy intake and high fecal T3 concentrations, thereby supporting state-dependent foraging. Although fecal GC did not vary strongly with energy reserves, individuals with higher fecal GC tended to have fewer energy reserves and substantially greater energy intake than those with low fecal GC. Consequently, individuals with greater energy intake had both high fecal T3 and high fecal GC concentrations, a pattern inconsistent with previous documentation from captive animal studies. We posit that a positive relationship between GC and T3 may be expected in animals exhibiting state-dependent foraging if GC is associated with increased foraging and energy intake. Thus, we recommend that additional investigations of GC– and T3–energy relationships be conducted in free-ranging animals across a diversity of body size and life-history strategies before these endocrine markers are applied broadly to wildlife conservation and management.

The experimental results show that initial damage has a clear effect on the creep behavior of rock. However, among the current creep models for rock, few consider the effect of the initial damage state. In the present study, a new nonlinear creep damage model for rock is proposed based on multi-loading creep tests of sandstone with different initial damage levels. The new model is composed of four components, a Hooke body, a Kelvin body, an improved viscous element, and a new nonlinear visco-plastic damage component. The creep damage model can not only describe the three typical creep stages (primary creep, secondary creep and tertiary creep) but also show the effect of initial damage on the creep failure stress. The parameters of the nonlinear creep damage model are obtained using the nonlinear least squares method. A unified set of creep parameters is proposed to predict the creep behavior of sandstone in different initial damage states. The agreement between the experimental data and numerical prediction demonstrates the applicability of the proposed model.

In the animal kingdom, threat information is perceived mainly through vision. The subcortical visual pathway plays a critical role in the rapid processing of visual information-induced fear, and triggers a response. Looming-evoked behavior in rodents, mimicking response to aerial predators, allowed identify the neural circuitry underlying instinctive defensive behaviors; however, the influence of disk/background contrast on the looming-induced behavioral response has not been examined, either in rats or mice. We studied the influence of the dark disk/gray background contrast in the type of rat and mouse defensive behavior in the looming arena, and we showed that rat and mouse response as a function of disk/background contrast adjusted to a sigmoid-like relationship. Both sex and age biased the contrast-dependent response, which was dampened in rats submitted to retinal unilateral or bilateral ischemia. Moreover, using genetically manipulated mice, we showed that the three type of photoresponsive retinal cells (i.e., cones, rods, and intrinsically photoresponsive retinal ganglion cells (ipRGCs)), participate in the contrast-dependent response, following this hierarchy: cones > > rods > >  > ipRGCs. The cone and rod involvement was confirmed using a mouse model of unilateral non-exudative age-related macular degeneration, which only damages canonical photoreceptors and significantly decreased the contrast sensitivity in the looming arena.