Lutz Reiter

Open source tracking and analysis of adult Drosophila locomotion in Buridan's paradigm with and without visual targets

Background Insects have been among the most widely used model systems for studying the control of locomotion by nervous systems. In Drosophila, we implemented a simple test for locomotion: in Buridans paradigm, flies walk back and forth between two inaccessible visual targets [1]. Until today, the lack of easily accessible tools for tracking the fly position and analyzing its trajectory has probably contributed to the slow acceptance of Buridans paradigm. Methodology/Principal Findings We present here a package of open source software designed to track a single animal walking in a homogenous environment (Buritrack) and to analyze its trajectory. The Centroid Trajectory Analysis (CeTrAn) software is coded in the open source statistics project R. It extracts eleven metrics and includes correlation analyses and a Principal Components Analysis (PCA). It was designed to be easily customized to personal requirements. In combination with inexpensive hardware, these tools can readily be used for teaching and research purposes. We demonstrate the capabilities of our package by measuring the locomotor behavior of adult Drosophila melanogaster (whose wings were clipped), either in the presence or in the absence of visual targets, and comparing the latter to different computer-generated data. The analysis of the trajectories confirms that flies are centrophobic and shows that inaccessible visual targets can alter the orientation of the flies without changing their overall patterns of activity. Conclusions/Significance Using computer generated data, the analysis software was tested, and chance values for some metrics (as well as chance value for their correlation) were set. Our results prompt the hypothesis that fixation behavior is observed only if negative phototaxis can overcome the propensity of the flies to avoid the center of the platform. Together with our companion paper, we provide new tools to promote Open Science as well as the collection and analysis of digital behavioral data.

Exploratory behaviour of honeybees during orientation flights

Honeybees, Apis mellifera, perform exploratory orientation flights before they start foraging in order to become familiar with the terrain. To reveal the structure of consecutive orientation flights and hence gain insight into exploratory behaviour, we monitored individual bees from their first flight onwards using harmonic radar technology for flight tracking. We categorized flights into short- and long-range orientation flights. (1) Short-range flights are likely to be related to learning the specific features of the hives immediate surroundings, and were performed significantly more frequently under unfavourable weather conditions. (2) The duration of long-range orientation flights declined from the first to the fourth flight because the bees spent less time inspecting the immediate surroundings of the hive. (3) Parts of single orientation flights were guided by extended parallel landscape structures on the ground. (4) During consecutive orientation flights bees explored novel sectors of the terrain. (5) Foraging flights performed after orientation flights covered greater distances and may involve a sector of the terrain not explored before, indicating that the acquired visual information plus path integration is sufficient for successful homing even from unfamiliar areas. (6) Exploration may be mixed with foraging flights after the initial orientation flights, sometimes leading to extremely long and elaborate flights. The latter are interpreted as being performed by scout bees. The results are interpreted within the frame of the psychology of exploratory behaviour in animals.

Honeybees Learn Landscape Features during Exploratory Orientation Flights.

Exploration is an elementary and fundamental form of learning about the structure of the world [1-3]. Little is known about what exactly is learned when an animal seeks to become familiar with the environment. Navigating animals explore the environment for safe return to an important place (e.g., a nest site) and to travel between places [4]. Flying central-place foragers like honeybees (Apis mellifera) extend their exploration into distances from which the features of the nest cannot be directly perceived [5-10]. Bees perform short-range and long-range orientations flights. Short-range flights are performed in the immediate surroundings of the hive and occur more frequently under unfavorable weather conditions, whereas long-range flights lead the bees into different sectors of the surrounding environment [11]. Applying harmonic radar technology for flight tracking, we address the question of whether bees learn landscape features during their first short-range or long-range orientation flight. The homing flights of single bees were compared after they were displaced to areas explored or not explored during the orientation flight. Bees learn the landscape features during the first orientation flight since they returned faster and along straighter flights from explored areas as compared to unexplored areas. We excluded a range of possible factors that might have guided bees back to the hive based on egocentric navigation strategies (path integration, beacon orientation, and pattern matching of the skyline). We conclude that bees localize themselves according to learned ground structures and their spatial relations to the hive.

Trajectory parameters of real flies and computer-generated data (grouping codes given below the graph).

Both A. Meander (turning angle divided by speed) and B. stripe deviation are similar in fly and computer-generated data. Red line denotes 45°, the mean value for computer-generated data. C–D. Centrophobism score for sitting (C) or for moving (D) is positive only for fly data. E. The distance traveled is different between the three types of data. Bars represent means and error bars standard errors, asterisks denote significant differences after a MANOVA analysis, n = 20 in each group.

Calculation of angles and number of walks.

A. The inner circle represents the platform, while the outer circle represents the arena and the light source (to scale). The bars represent the stripes (wide or narrow). Considering the movement from P₀ to P₁, α₀ is the absolute movement angle (similarly α₋₁} is the absolute movement angle of the movement P₋₁} to P₀). The turning angle γ can be calculated as α₀ - α₋₁}, it represents the change in direction at time 0. β is the “stripe deviation” angle, the angle from the movement to a vector going straight toward the middle of the stripe that is in the direction of the movement. In the “ltraj” object, α is assigned to P₀, β to P₁. Gray areas denote the sectors used to start and end a walk between stripes: a walk is counted for each passage from one gray area to the other. B. Trajectory example, zoomed on the platform size. The disposition of the stripes are at 90 and −90° as in A. Dots represent the position of the fly during the three first minutes of a test with narrow stripes, after down sampling to 10 Hz.

Fly trajectory metrics for endogenous locomotion (gray bars), Buridan's paradigm with narrow stripes (white bars) or wide stripes (striped pattern)

A. In the presence of visual targets, the fly shows more walks between the stripes than in their absence. B. Median stripe deviation is different in the three groups. Red line denotes the value for random walks. C. Centrophobism during pauses is still present in all three groups. D. Centrophobism while moving is eliminated by narrow stripes. E. Median speed is not significantly affected by visual targets. F. The number of pauses is lower in the wide stripe condition as compared to the two other conditions. Asterisks denote significant differences after a MANOVA analysis. Bars represent means and error bars standard errors, n = 20 in each group.