Free-Flight Odor Tracking in Drosophila Is Consistent with an Optimal Intermittent Scale-Free Search

During their trajectories in still air, fruit flies (Drosophila melanogaster) explore their landscape using a series of straight flight paths punctuated by rapid 90° body-saccades [1]. Some saccades are triggered by visual expansion associated with collision avoidance. Yet many saccades are not triggered by visual cues, but rather appear spontaneously. Our analysis reveals that the control of these visually independent saccades and the flight intervals between them constitute an optimal scale-free active searching strategy. Two characteristics of mathematical optimality that are apparent during free-flight in Drosophila are inter-saccade interval lengths distributed according to an inverse square law, which does not vary across landscape scale, and 90° saccade angles, which increase the likelihood that territory will be revisited and thereby reduce the likelihood that near-by targets will be missed. We also show that searching is intermittent, such that active searching phases randomly alternate with relocation phases. Behaviorally, this intermittency is reflected in frequently occurring short, slow speed inter-saccade intervals randomly alternating with rarer, longer, faster inter-saccade intervals. Searching patterns that scale similarly across orders of magnitude of length (i.e., scale-free) have been revealed in animals as diverse as microzooplankton, bumblebees, albatrosses, and spider monkeys, but these do not appear to be optimised with respect to turning angle, whereas Drosophila free-flight search does. Also, intermittent searching patterns, such as those reported here for Drosophila, have been observed in foragers such as planktivorous fish and ground foraging birds. Our results with freely flying Drosophila may constitute the first reported example of searching behaviour that is both scale-free and intermittent

Dopamine Modulates the Rest Period Length without Perturbation of Its Power Law Distribution in Drosophila melanogaster

We analyzed the effects of dopamine signaling on the temporal organization of rest and activity in Drosophila melanogaster. Locomotor behaviors were recorded using a video-monitoring system, and the amounts of movements were quantified by using an image processing program. We, first, confirmed that rest bout durations followed long-tailed (i.e., power-law) distributions, whereas activity bout durations did not with a strict method described by Clauset et al. We also studied the effects of circadian rhythm and ambient temperature on rest bouts and activity bouts. The fraction of activity significantly increased during subjective day and at high temperature, but the power-law exponent of the rest bout distribution was not affected. The reduction in rest was realized by reduction in long rest bouts. The distribution of activity bouts did not change drastically under the above mentioned conditions. We then assessed the effects of dopamine. The distribution of rest bouts became less long-tailed and the time spent in activity significantly increased after the augmentation of dopamine signaling. Administration of a dopamine biosynthesis inhibitor yielded the opposite effects. However, the distribution of activity bouts did not contribute to the changes. These results suggest that the modulation of locomotor behavior by dopamine is predominantly controlled by changing the duration of rest bouts, rather than the duration of activity bouts

Tracking nutrient decisions in Drosophila melanogaster

Animals integrate external sensory information and current metabolic needs to adapt their behavior in order to survive. Accordingly, many organisms can detect an internal nutritional imbalance and adjust their nutritional choices to restore homeostasis. Detailed quantitative analyses of nutrient-choice behaviors are needed to deepen our understanding of how neural circuits integrate internal state information and drive compensatory behavior when facing metabolic challenges. During this project, we developed an automated video tracking setup to characterize how metabolic and reproductive states interact to shape exploitation and exploration decisions taken by the adult fruit fly Drosophila melanogaster, to achieve nutritional homeostasis. We find that these two states have specific effects on the decisions to stop on and leave proteinaceous food patches. Furthermore, the internal nutrient state defines the exploration-exploitation trade-off: nutrient deprived flies focus on specific patches while satiated flies explore more globally. We provide few examples of how our paradigm could be used in the dissection of the genetic and neuronal pathways underlying nutrient decisions: First, we show that olfaction is not required for the compensatory high yeast feeding after amino acid deprivation, but that it mediates the efficient recognition of yeast as an appropriate food source in mated females. Second, we show that octopamine is required to mediate homeostatic postmating responses without affecting internal nutrient sensing. Third, we show how gustation is required to sustain interest for protein-rich resources upon amino acid deprivation. Our results provide a quantitative description of how the fly changes behavioral decisions to achieve homeostatic nutrient balancing and provide a framework for future detailed mechanistic dissection of such decisions

Finding an assay that reveals effects of sleep deprivation on decision making in Drosophila

This study makes use of cutting-edge technology to tackle the intricate links between decision making and sleep in the Drosophila Melanogaster fly using various innovative behavioural paradigms. The assays developed are iteratively improved to be suitable for high-throughput experiments and automatic video tracking of desired features. The final paradigm presents the fly with the simple decision of passing through two holes of different sizes: a large hole through which it can pass easily and a smaller one through which it can pass with some difficulty. Independently of the external conditions such as light, shape of the assay and time of the day or of the internal states such as genetic background and sleep state, all the flies choose to make multiple passages through both holes and unanimously show a preference for the bigger hole. Our paradigm is unique in that it allow us to assess flies decisions independently of the locomotion state by evaluating the proportion of passages through the two holes. Remarkably, this parameter is conserved in the same genetic background. Moreover, our results confirm and strengthen previous studies showing that locomotion is increased by space restriction in males. When faced with our non-conventional paradigms, after prolonged sleep deprivation, flies suppress their sleep rebound. In addition, they show no behavioural differences to control flies. It appears that the sleep pressure built up through homeostatic regulation is not important enough to counteract the in- creased arousal state resulted from space restriction in order to trigger sleep. However, when experiments are performed in the afternoon during flies ”siesta”, they fall asleep, indicating that the sleep pressure arising from circadian regulation is more significant than the sleep pressure coming from homeostatic regulation.Open Acces

A Theory for Complex Systems Social Change: An Application of a General ‘Criticality’ Model

Within the developed nations deterioration in the basis of society, as dramatically demonstrated by the Lehman collapse, has reached extreme levels, and currently the formation of pro-change agents is approaching a decisive stage. Here, we will construct a complex systems \u27criticality\u27 model, apply it to social change, and examine its reliability and validity. The model derived a power law distribution of the output of social change. The validity of the model was verified by examining vote shares of parties in Japan. Based on the results of this examination, we propose a new quantitative strategy “information entropy enhancement” for social change

A Theory for Complex Systems Social Change: An Application of a General ‘Criticality’ Model

Within the developed nations deterioration in the basis of society, as dramatically demonstrated by the Lehman collapse, has reached extreme levels, and currently the formation of pro-change agents is approaching a decisive stage. Here, we will construct a complex systems \u27criticality\u27 model, apply it to social change, and examine its reliability and validity. The model derived a power law distribution of the output of social change. The validity of the model was verified by examining vote shares of parties in Japan. Based on the results of this examination, we propose a new quantitative strategy “information entropy enhancement” for social change

A statistical mechanics approach to random searches

Orientador: Prof. Dr. Marcos Gomes E. da LuzTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Curso de Pós-Graduação em Física. Defesa: Curitiba, 18/02/2016Inclui referências : f. 105-115Resumo: O tópico desta tese é a aplicação de modelos de busca aleatória em uma coleção de problemas multi-disciplinares. Foram desenvolvidos modelos simples que reproduzem (aproximadamente) o comportamento complexo dos problemas que escolhemos. As primeiras aplicações consideram o problema do forrageamento biológico, onde estudamos numericamente evidências que suportam a otimização por buscas de Lévy. Em seguida, desenvolvemos um modelo de distribuição de alvos dinâmica e estudamos a emergência da estacionariedade neste problema. Um modelo para a otimização computacional de buscas em ambientes homogêneos foi elaborado utilizando ferramentas de paralelização. Numa aplicação direta de buscas aleatórias, estudamos o forrageamento de larvas da mosca da fruta Drosophila melanogaster em um modelo numérico e através de uma abordagem experimental. Utilizamos um procedimento novo para caracterizar a busca aleatória através de processos estocásticos. Um método espectral foi aplicado na reconstrução do ambiente de busca utilizando a matriz de transição do processo. O último trabalho foi um estudo de um modelo que descreve, através da mecânica estatística, um processo evolucionário. Desenvolvemos um tratamento termodinâmico para interpretar as transições de fase do processo, bem como empregamos técnicas de simulated annealing para obter configurações mais robustas do modelo. Palavras-chave: busca aleatória, vôos de Lévy, mecânica estatística, processos estocásticos.Abstract: The topic of this thesis is the application of random search models in a collection of interdisciplinary problems. We developed simple models that can reproduce (at some extent) the complex behavior present in the problems that we have chosen. The first applications concerned animal foraging, where the robustness of the Lévy flight foraging hypothesis was numerically studied. We developed a model of a dynamic distribution of targets and studied the emergence of the stationarity in this new problem. A parallel optimization method was designed to reduce the computational costs in random search simulations, and was proved efficient in homogeneous search environments. In a direct application of random search models, we studied the dual foraging behavior of Drosophila melanogaster larvae with both a numerical and an experimental approach. A new procedure was applied in the study of random searches using a stochastic process formulation. In this problem, a spectral method was developed to reconstruct the geometry of the targets distribution using only the transition matrix of the search process. The last work was the study of a model that describes the evolutionary process using a statistical mechanics approach. We designed a thermodynamics interpretation of the transitions between stasis and hectic phases in the model and applied simulated annealing techniques to reach longer stasis configurations. Keywords: random search, Lévy flights, statistical mechanics, stochastic processes