Dept. of Behavioral and Cognitive Biology, Faculty of Life Sciences, University of Vienna

1. Consistency and plasticity in wild raven's grouping, foraging and anti-predator decisions

Social life constitutes a very dynamic environment, where individuals need to regularly update information and adjust to others' behaviour. Individual differences in dealing with the social environment may result in fitness consequences and as such may form the basis for the evolution of socio-cognitive skills. Given the key role of inter-individual variation for evolutionary concepts, surprisingly little is known about how consistent, or plastic, individuals are in their social decision making over time and/or across context. In part, such questions are covered by research on animal personalities, defined as consistent inter-individual differences. While this field has made much progress in the last decades, the focus has been largely on non-social personality traits (e.g. boldness/shyness, exploration/avoidance), whereas traits based on social behaviour (e.g. dominance, sociability) have received comparably little attention. Furthermore, few attempts have been made to reconcile ideas of animal personality with the flexibility and plasticity shown in social foraging and social learning (e.g. frequency dependent, model-based strategies).
The aim of this project is to address inter-individual variation in wild ravens' behaviour within and across context. Ravens are an excellent study species in this respect as they show a rich behavioral repertoire, advanced socio-cognitive skills and complex social structure as non-breeders, forming groups with changing group compositions.
The proposed research will take advantage of our unique setting for studying free-ranging, individually marked ravens, and combine behavioral observations with experimental approaches (e.g. acoustical playbacks) and GPS tracking. The candidate shall investigate how consistent/flexible individual ravens behave i) when they form (sub)groups for foraging, roosting and socializing, ii) when they forage at sites of different predation risk, iii) when they scrounge food from conspecifics and heterospecifics and iv) when they receive auditory information about predators.

Dept. of Behavioral and Cognitive Biology, Faculty of Life Sciences, University of Vienna

1. Comparative Neural Basis of Music and Speech (with Leonida Fusani & Ludwig Huber)

Certain perceptual and cognitive aspects of music and speech appear to be based on mechanisms shared with other animals, but the neural basis of these, and the role of environmental stimuli in shaping them, remains unclear [1]. This project will use non-invasive neural recordings (EEG in pigeons and dogs [2], fMRI in dogs [3]) to gain a clearer picture of the mechanisms underlying music perception (both rhythmic and metrical structure, and the harmonic structure of chord sequences – both aspects of “musical syntax”), along with speech processing (the perception of lexical stress and of vowels). Such methods have only recently been applied to animals and have already provided important insights into shared mechanisms underlying complex auditory perception [4]. By comparing brain activations for music and speech we can determine if overlapping brain regions are activated (as for humans) or different neural circuits are involved. We will also examine the effect of environment in dogs by studying animals with more or less exposure to music in their homes (e.g. music teachers vs. owners who prefer silence at home): if the results are promising this could potentially be extended to kennel- or pack-living dogs to titrate exposure to human speech in the future. 

2. High-throughput bioacoustics analysis of social communication in geese (with Sonia Kleindorfer)

We will use continuous acoustic monitoring of greylag goose vocalization (using wireless collars), combined with video, acoustic camera (audio/video localization) and physiological and behavioral data to develop a detailed vocal repertoire of the greylag goose, tied to their ethogram. This will use Python and Praat along with data science (hierarchical cluster analysis) and machine learning approaches (LASSO) to process the huge volume of data. We will use playback experiments, using as dependent measures both behavioral responses (looking time) and physiological responses (heart rate acceleration), to address questions of social preference (grounded in social network analysis). Finally, we will address the causal role of vocalization in group behaviors, for example to determine whether group movements are preceded by particular vocalizations from particular individuals (e.g. using Granger causality and similar measures). 

Dept. of Behavioral and Cognitive Biology, Faculty of Life Sciences, University of Vienna & Dept. of Interdisciplinary Life Sciences, Konrad Lorenz Institute of Ethology, University of Veterinary Medicine Vienna

1. Motor learning of courtship displays

Courtship includes often bizarre and elaborate displays where animals exhibit ornaments – i.e. modified and brightly coloured feathers - while performing ritualized movements. Many of the displayed traits are rather static, for example feathers are grown during periodic moult, whereas other undergo seasonal changes and are fully developed only during the breeding season. Courtship behavior is typically shown only in the initial phases of sexual interactions and may involve complex sequences of repeated motor patterns. There is increasing evidence that the coordination of series of motor patterns composing the full courtship is obtained via motor learning. Juvenile males of many species of lekking birds such as manakins and bowerbirds are often seen observing adult males, rehearsing rudimentary versions of the display, and a few studies have demonstrated that motor learning plays a role in the establishment of a display choreography. The new project will build on ongoing work conducted in Central America and Australia and will be based on longitudinal studies of the behavior of individual male birds to understand if and how components of the courtship are learned from or with the guidance of other individuals.

2. Comparative aesthetics and multimodal signalling

Many animal signals are multimodal in that they include components that occupy different sensory channels. Typical examples are the parades or dances of a number of insect and bird species, where acoustic and visual signals are combined. Despite some theoretical interests in the last decades and a few empirical studies in recent years, the function of multimodality remains mostly unknown. Among currently theories we found those that advocate that multiple concurrent signals are redundant and act as back-up signals in case communication in one channel is disrupted; that they amplify each other; that they induce increased attention in the receiver. A few studies, however, suggest that multiple signals may combine to produce an integrate signal that could be object of evaluation by the receiver. In this perspective, we have started working on a biological concept of aesthetics to explore whether the holistic evaluation of elaborate signals involve similar neural processes in different species. The new project will develop from ongoing research with domestic doves and humans for which we are developing innovative testing protocols.

Dept. of Developmental and Educational Psychology, Faculty of Psychology, University of Vienna

1. Neural entrainment to naturalistic auditory rhythms in infants and its relation to the early language development

Brain activity is characterized by rhythmic oscillations indicating dynamic fluctuations in the excitability of neurons. In human adults, entrainment of these neuronal oscillations to the rhythm of speech has been related to enhanced signal processing and effective communication. It is currently unclear whether neuronal entrainment already plays a role in early language acquisition and which types of stimuli allow for optimized auditory processing in infants. In this longitudinal study, a sample of infants will be tested at three time points (at 6, 12 and 24 months) longitudinally. At each time point, we will measure infants’ electroencephalogram (EEG) while they are listening to a range of naturalistic auditory stimuli, in particular infant-directed and adult-directed speech and singing. In addition, at 24 months, we will assess children’s language abilities with standardized measures. Our hypotheses are that 1) infants’ neuronal oscillations will preferentially align with infant-directed speech rhythms, which are closer to the peak frequencies of their endogenous neuronal oscillations than adult-directed speech, and 2) infants with higher levels of entrainment to speech and singing at 6 and 12 months should have a language processing advantage resulting in increased language skills at 24 months. The PhD candidate will acquire state-of-the-art expertise in EEG data acquisition and analysis in addition to developmental diagnostics of early communication skills. This research has important implications for early human language acquisition and links to Angela Stoeger’s work on vocal learning and rhythm in different species.

Messerli Research Institute, Unit of Comparative Cognition, University of Veterinary Medicine Vienna

1. Over-imitation in dogs and human children

Dogs have not only shown different kinds of social learning, from either conspecifics or humans, including do-as-I-do imitation, deferred imitation, and selective imitation, but in two previous studies they have also shown an eagerness to copy causally irrelevant actions. This so-called over-imitation is prevalent in humans, especially children, but is totally absent in great apes. Whereas in one of two previous studies a reasonable number of the dogs copied the irrelevant actions from their human caregiver (Huber et al., 2018), only very few did so when the actions were demonstrated by a stranger (Huber et al., 2020). We therefore assumed that over-imitation in dogs might be strongly motivated by social factors, such as affiliation or conformity. Dogs have not only been domesticated to live and work with us, but many companion dogs develop strong affiliative relationships with their caregiver, which are akin to the attachment bonds between human children and their mother. In this PhD study we would confront dogs with the same demonstration of causally relevant and irrelevant actions as in the previous studies, but this time with caregivers of various relationships (in a range of weakly to strongly attached) to their dogs as the demonstrator. The human-dog bond would be determined by using classical attachment tests, such as Ainsworth strange situation test. We hypothesize that the eagerness of dogs to learn from humans and to copy even unnecessary actions is strongly facilitated by their relationship with the particular human. Finally, to see if over-imitation in dogs is based on the same socio-cognitive processes as in human children, we would start a cooperation with a new Faculty member of the DK, Stefanie Hoehl, an expert in over-imitation in humans (e.g., Hoehl et al., 2019).

2. Social tactics of free-ranging pigs

The main goal of this PhD project is to test the hypothesis - implicit in most theories of the evolution of advanced cognition - that socio-cognitive abilities become apparent in groups of social animals if they a) are kept in conditions similar to the natural environment and b) if they are forced to use those abilities in appropriate, challenging circumstances, such as in competitive foraging tasks. To test this hypothesis, we will conduct a series of experiments that have been used in the literature to examine the socio-cognitive abilities of non-human animals. So far mainly species with advanced skills in both the social and technical domain, like primates and corvids, have been used. To control for the confounding factor of technical intelligence as the driving force of the evolution of intelligence, one needs to test animals with only modest abilities in the technical domain. Pigs seem to be a perfect candidate. They show a number of features indicative of social complexity but as omnivores only modest technical skills. Importantly, to bring their true potential in the social domain to the front, we will conduct the studies on free-ranging pigs (kept in semi-natural environments), where they (slowly) grow up, forage naturally, develop a natural group structure (sounder) and live for years. Experiments will be conducted to test their tactical behavior building on well-proven tasks such as the 'informed forager' paradigm. The few experiments conducted so far with this aim have tested commercially reared pigs living for few months in artificially formed groups.

Dept. of Behavioural and Cognitive Biology, Faculty of Life Sciences, University of Vienna

1. Does prenatal sound experience affect gene expression and vocalization behavior?

For species with imitative vocal learning, a core research challenge is to identify when learning begins. Traditionally, adequate developmental state of the neural substrates for vocal learning was thought be reached well after hatching in songbirds. New research shows that gene activity and vocal learning change as the consequence of sound experience in ovo. Zebra finch (Taeniopygia guttata) embryos exposed to prenatal conspecific song had increased ZENK activity and superb fairy-wren embryos (Malurus cyaneus) discriminated conspecific calls and produced a prenatally learnt call shortly after hatching. Nothing is known about individual in ovo response to sound in vocal non-learning systems. The aim of this study is to investigate if avian embryos from vocal learning and vocal non-learning lineages differ in their response to sound in ovo and if prenatal acoustical experience alters gene expression and vocalization behavior post-hatch. The study systems are vocal learning fairy-wrens (Maluridae) and vocal non-learning greylag geese (Anatidae). Using habituation/dishabituation research approaches, non-invasive prenatal digital heart rate monitors, and post- hatch blood sampling and vocalization recordings across life stages, this work will combine behavioral, bioacoustical, physiological and molecular approaches to measure the genetic and behavioral downstream effects of prenatal sound experience and response to sound across avian taxa.

2. Consistency in prenatal physiology across life stages and effects on personality

Individual differences in physiological characteristics or behaviours that are consistent and repeatable across contexts are known as 'consistent individual differences' and are commonly found across taxa. Consistent individual differences in resting metabolic rate (i.e., the number of calories that the body burns while resting) have been suggested to promote and support consistent individual differences in development and behaviour. Resting metabolic rate is an important proximate mechanism simply because all processes in the body require energy. Thus, the persistence of consistent individual differences may reflect behavioural and physiological trade-offs: individuals with higher resting metabolic rates may be more exploratory but may be more susceptible to starvation because of increased energetic requirements. Consistent individual differences in resting metabolic rate and behaviours may also represent different aspects of a general slow-fast life-history continuum, where fast-growing individuals with higher resting metabolic rate are expected to be more active, and have higher energetic needs, than those with slower metabolic rate. It is not clear if an embryo with a low metabolic rate develops into an adult with a slow metabolic rate. That is, there is a gap in knowledge about whether metabolic rate is consistent across life stages. A clear framework linking resting metabolic rate across life stages, and how metabolic rate is associated with activity versus exploration or other measures if individual differences, is missing. Building on preliminary data in the Northern Bald Ibis (Geronticus eremita) studied at the Konrad Lorenz Research Center, this project has the following aims:

Dept. of Cognition, Emotion and Methods in Psychology, Faculty of Psychology, University of Vienna

The two projects I am proposing here serve as a general orientation towards a novel research line on environmental social cognitive neuroscience, which I want to pursue in the next few years. Thus, Ph.D. applicants are encouraged to also come forward with their own research ideas falling into that general research line. This research line encompasses topics such as what shapes human attitudes towards their (natural) environment, including other animals, how that influences their thoughts, feelings, well-being, and in particular what impact has this on pro-environmental and pro-ecological decisions and more sustainable behaviors. To this end, I will predominantly pursue a cognitive and neuroscience laboratory-based approach, which aims to advance our understanding of the neuro-cognitive correlates and ultimately mechanisms of pro-environmental behavior, and possibly complement it by "real life" field-based studies, including e.g. (online) surveys, ecological momentary assessments, and big data analyses.

1. The restorative potential of natural environments

Feeling connected to and being exposed to natural environments has been shown to have a positive impact on mental and physical health, mood and well-being, and stress resilience. With a few notable exceptions (e.g. Bratman et al., PNAS 2015), most of that work has relied on self-report or other types of psychological and behavioral data. The aim of this dissertation project is to develop and test a theoretical framework that connects the behavioral and psychological data to neuromechanistic approaches that may explain by which cognitive, affective and neural mechanisms nature exerts these effects on our minds, brains, and bodies. To this end, laboratory based research using brain imaging and cognitive-behavioral methods (e.g. eye tracking, decision making experiments) shall be combined with "real life" measures of actual responses to nature exposure (either in the same or different samples of participants). Ultimately, the aim is to investigate whether and how individual differences in being susceptible to the positive restorative effects of nature exposure influence pro-environmental decision making and behavior, both on an individual and a macro-level.

2. Attitudes of humans towards canines - friendly dogs, fierce wolves?

The current recovery of wolves across Europe has engendered fierce debates with some extreme cases of anti-wolf sentiment. While obviously wolves can pose a danger to humans, there have been few incidents in the last centuries, even in areas where the wolf was not extinct; in contrast, attitudes towards dogs are largely positive, despite several thousand incidents world-wide with both family and wild-living dogs. This poses the question why a good part of the human population reacts so strongly against the recolonization of wolves, and why subjective attitudes towards dogs and wolves do not always seem to align with objective statistics on their harm potential. Scientific evidence on our attitudes towards wolves and dogs is not only scant but with very few exceptions stems from the use of self-report methods, such as questionnaires. In this dissertation project, social psychological theories on contact theory and social neuroscience approaches including brain imaging, will be combined with knowledge about dog and wolf behavior. The overarching aim is to unravel the social, cognitive and neural mechanisms that drive our attitudes towards dogs and wolves.

Domestication Lab, Dept. of Interdisciplinary Life Sciences, Konrad Lorenz Institute of Ethology, University of Veterinary Medicine Vienna

1. Socio-ecological cognition: Rules of thumb in free-ranging dogs

Socioecological hypotheses are usually highly complex and multivariate, and predictions highly sensitive to sometimes small changes. Hence animals may use simple rules of thumb rather than sophisticated computations to optimize their behavior under the current socioecological conditions, and such simple rules may often provide good approximations but also result in implemented socio-ecologies that deviate from those theoretically predicted. Our project will focus on the social-tolerance-tradeoff where dominants must balance their high-gain resource monopolization potential against concessions towards subordinates which may otherwise cease support during collective resource defense against outgroup competitors (Sterck et al. 1997). Social tolerance should increase with interdependency for collective resource defense, and be promoted by relatedness (Lukas et al. 2018). However, between-group competition is difficult to estimate, and animals may therefore just bookkeep the general rate of collective defense activity as an approximation (as also researchers often do). Moreover, in particular paternal kin recognition may often be best achieved using familiarity or phenotype similarity as a proxy (Widdig 2007).

Here we will investigate these mechanisms on our established free-ranging dog field site in a coastal tourist area in Morocco by collecting DNA-samples and comprehensive behavioral data. We will particularly utilize the strong tourist seasonality at the field site, resulting in low between group competition and frequent opportunity for pseudo-defense interactions during the peak season, and vice versa during the low season. This project will be co-supervised by Andreas Berghänel and benefit through collaboration with Thomas Bugnyar (DK Faculty).

2. Proximate mechanisms underlying problem solving abilities

Problem solving abilities are thought to be shaped by natural selection as a response to the species-specific challenges of their social-ecological environment (Byrne, 1997). Considering the weight of phylogeny in accounting for potential similarities between species, the most common approach to evaluate this is by comparing closely related species that differ in key traits thought to be evolutionarily relevant, e.g. their social structure and/or feeding ecology. Wolves and dogs, although closely related to each other, vary significantly in several factors of their social and ecological environments (see Marshall-Pescini et al., 2017 for a review). They also show marked differences in their problem-solving abilities, with wolves often outperforming dogs. However, it is unclear whether this difference comes from their cognitive abilities (e.g. learning and inferential reasoning), motivation (e.g. persistence and neophobia) or general-purpose mechanisms (e.g. attention, working memory) and which selective pressures have shaped them. Within the framework of the larger project, the PhD student we will start to investigate the general-purpose mechanisms. Selective attention i.e. the ability to focus on relevant information while inhibiting signals from irrelevant stimuli (Olsen, 2018), working memory capacity (WMC) and inhibitory control are thought to be crucial in solving problem-solving tasks. Here we will use several different tasks to measure attentional control and working memory, visual attention and inhibition.

This project and thus the supervision of the PhD student will be conducted together with Sarah Marshall-Pescini who focuses her research on the influence of the social ecology on the cognitive abilities of dogs and wolves and Sabine Tebbich (DK Faculty member), whose expertise lies in physical cognition in various animal species.

Dept. of Behavioral and Cognitive Biology, Faculty of Life Sciences, University of Vienna

1. Rhythmic entrainment and timing in elephants

In the last decade clear evidence has accumulated that elephants are capable of vocal production learning. Examples of vocal imitation are documented in African (Loxodonta africana) and Asian (Elephas maximus) elephants (reviewed in 1), but little is known about the function of vocal learning within the natural communication systems of either species. We are also just starting to identify the neural basis of elephant vocalizations. The African elephant diencephalon and brainstem possess specializations related to aspects of neural information processing in the motor system (affecting the timing and learning of trunk movements) and the auditory and vocalization system (1). The vocal learning and rhythmical entrainment hypothesis raised by Patel (2) suggests that a direct connection between the auditory centers and the motor planning regions (typical for vocal learners) is a prerequisite for the ability to synchronize with an auditory beat. This implies that only vocal learning species should be capable of rhythmical entrainment. Following this idea, elephants should, in theory, be capable of rhythmical entrainment. So far, an Asian elephant has been observed drumming a stable beat (3), and elephants in Asian tourist shows move rhythmically to music. Nonetheless, it remains unclear how much training was involved, whether the elephants spontaneously match their movements to the beat, or whether the accompanying music was chosen advantageously.

Within the frame of the proposed PhD project, elephants of both species will be tested on their abilities to synchronize their movements to rhythmic sounds.
Much of the group coordination in elephants - splitting up and reuniting which is typical for the fission- fusion society of elephants - is done via vocalizations (4), but little is known about timing abilities of elephants in the vocal domain. Therefore, timing and turn taking in communicative events (like in chorusing, and antiphonal contact calling) will further be investigated. Untangling the evolutionarily relationship between vocal learning, rhythmical entrainment and timing abilities (accurate timing is crucial in human speech and music) requires testing multiple species including non-vocal learners, however, equally important is investigating whether all vocal learners indeed possess the ability for rhythmical entrainment.

2. Cheetah sexual communication

In most mammals, vocal communication plays an important role during mating and reproduction. In several species, vocal signals have been shown to convey aspects of male quality used to attract females (1,2). Here, acoustic cues to the caller's physical attributes such as size, maturity or hormonal state are likely to be important but acoustic cues strongly vary depending on the mating system (3). Also, the importance and relevance of acoustic signals in relation to other modalities varies among species. Felidae are a highly vocal but considerably little studied mammalian family in terms of vocal behavior in general, and sexual communication in particular.

The aim of this project is to gain a better understanding of how vocal signaling mediates reproduction in Felidae with a focus on a highly endangered species, the cheetah (Acinonyx jubatus). Cheetahs produce a variety of vocalizations in a broad range of contexts (4), however, only little is known about the significance and the information conveyed by these signals. Cheetahs (as other cat species) produce vocalizations via two different laryngeal sound producing mechanisms, (1) via myoelastic-aerodynamic vocal fold vibration and vocal fold vibration via active muscle contractions ('purring'). Cheetahs particularly combine these mechanisms, which results in structurally complex transitional calls and combinations (4). Specifically in the mating context, both males and females do vocalize a lot, and males also constantly vocalize when encountering female odors. Thus, vocal displays seem a key factor for mate choice and also seem to initiate (perhaps even initiate estrous) and mediate mating behavior.
The proposed PhD thesis will take a broad bioacoustics and behavioral research approach by investigating and describing mating behavior and analyzing the structure and variation, the information content and the functional significance of male and female mating calls. Research will be conducted in zoological institutions in Europe and breeding sanctuaries in Southern Africa applying a multi-level methodological approach (including acoustic recordings, behavioral observations, taking physical measurements of trained cheetahs, fecal sampling for androgen / estrogen level analysis as well as conducting scent, and maybe, playback experiments).
In captive breeding programs, conservation managers intuitively use male vocalizations as an indicator of female receptiveness (pers. comm), however, females are extremely choosy and artificial insemination often is still the only way to successful reproduction. The findings of this PhD thesis shall improve knowledge of cheetahs' sexual communication in order to progress non-invasive assessment methods for breeding introductions leading to successful copulations.

Dept. of Behavioural and Cognitive Biology, Faculty of Life Sciences, University of Vienna

1. The role of play behavior in promoting innovativeness in birds and humans

One way that humans and other animal species can adapt to a changing environment is by changing existing behavior; another way is by inventing new solutions for environmental challenges. Innovations can either be seen as a process that results in new or modified learned behavior or as an end product which are new behaviors, and/or use pre-existing ones applied in new contexts (1). But how exactly does a new form of action emerge? It is still difficult to explain the origin of complex behavioral patterns. This is particularly so in examples where incomplete sections of the behavioral sequence are not rewarded. Which behavioral / cognitive components are involved? Why are some individuals, some populations or some species better at adapting and innovating? In 2016 I have proposed a framework for animal innovation in which we split innovation into factors (components and phases) that can be manipulated systematically, and investigated experimentally (2).
The aim of the proposed PhD- project is to combine approaches from biology, cognitive science and innovation studies to explore the bases of innovation in animals and humans, and to identify the internal (psychological and physiological) preconditions and components of behavioral innovations. A particular focus may be on testing the role of social and non-social play in the emergence of novel behavior with an experimental approach. Exploration and, to an even greater extent, play are two motivational systems leading to novel combinations that can be repeated over and over again without the requirement for any extrinsic reward (2,3). Model organisms to test this hypothesis are children and Goffin's cockatoos and other parrot species which are especially playful and highly innovative (4).

2. Early life stress and behavioral flexibility

Growing evidence suggests that social and ecological challenges experienced early in life can influence behavioral flexibility by shaping mechanisms of motivation and cognition during ontogeny (1-4). These ontogenetic effects might explain to a large extent the inter-individual variation in flexibility found in most animal species (e.g. reviewed in 3). An important mediator between early life experiences and later life cognitive performance is the vertebrate stress axis; exposure to early-life stressors may result in the persistent shaping of stress-axis reactivity, which in turn impacts the development of cognitive abilities and behavioral flexibility (4). The physiological stress response of vertebrates is an adaptive and highly efficient mechanism to cope with unpredictable, stressful situations as it mobilizes extra energy.
However, repeated or long-lasting disturbance will result in chronic activation of the stress axis, which may impair flexibility by shifting behavioral activation to inhibition (e.g. 5). The threshold between an adaptive "emergency" activation of the stress response and a harmful, pathological activation depends on the environmental conditions and the frequency and duration of activation (6). Individuals in poor nutritional condition are more susceptible to reach the emergency threshold that induces the onset of an adaptive stress response (6). It is puzzling, however, that individuals living under affluent conditions may remain in a chronic (and pathologically) activated state of the stress axis without actually reaching the emergency threshold (7).
Understanding of how early-life stress and nutrition, respectively, impact stress reactivity and how the latter affects behavioral flexibility is an interesting research objective but also highly relevant for the welfare of farm animals. Thus, the domestic pig is an ideal model organism for this topic as they have a complex social system, are fast learners but are often kept under poor condition in a high nutritional state. The influence of early life experience on stress reactivity and behavioral flexibility can be tested by varying husbandry (industrial animal husbandry vs. socially and environmentally enriched husbandry). The interaction between nutrition, stress reactivity and flexibility can be tested by varying long- and short-term stress levels in test groups with different nutritional states.