Abstract
Tracking animal movements such as walking is an essential task for understanding how and why animals move in an environment and respond to external stimuli. Different methods that implemented image analysis and a data logger such as GPS have been used in laboratory experiments and in field studies, respectively. Recently, animal movement patterns without stimuli have attracted an increasing attention in search for common innate characteristics underlying all of their movements. However, it is difficult to track the movements in a vast and homogeneous environment without stimuli because of space constraints in laboratories or environmental heterogeneity in the field, hindering our understanding of inherent movement patterns. Here, we applied an omnidirectional treadmill mechanism, or a servosphere, as a tool for tracking two-dimensional movements of small animals that can provide both a homogenous environment and a virtual infinite space for walking. To validate the use of our tracking system for assessment of the free-walking behavior, we compared walking patterns of individual pillbugs (Armadillidium vulgare) on the servosphere with that in two types of experimental flat arenas. Our results revealed that the walking patterns on the servosphere showed similar diffusive characteristics to those observed in the large arena simulating an open space, and we demonstrated that our mechanism provides more robust measurements of diffusive properties compared to a small arena with enclosure. Moreover, we showed that anomalous diffusion properties, including Lévy walk, can be detected from the free-walking behavior on our tracking system. Thus, our novel tracking system is useful to measure inherent movement patterns, which will contribute to the studies of movement ecology, ethology, and behavioral sciences.
Highlights
The most outstanding feature of animals is that they move around their environments to search for food, mates, and habitats or to avoid predators
In the past two decades, studies on trajectories of animal movements have reported that animals exhibit scale-free movements (i.e., Levy walks) or anomalous diffusion, which leads to efficient searches [3]
To compare movement patterns on the servosphere and the small arena, we reduced the frame frequency of both data to 5 frames per second (FPS), whereas to compare the movement pattern between the servosphere and the large arena, the rate frequency of the data was reduced to 0.1 FPS and location data were converted into corresponding lattices of the large arena
Summary
The most outstanding feature of animals is that they move around their environments to search for food, mates, and habitats or to avoid predators. The movements can be formed by internal and external factors [1]. The goal of behavioral ecology and neuroscience is to identify these factors forming animal movements and to understand why and how the animals move. In the past two decades, studies on trajectories of animal movements have reported that animals exhibit scale-free movements (i.e., Levy walks) or anomalous diffusion, which leads to efficient searches [3]. The Levy walks are described as a combination of many short movement steps and rare long-distance displacements. The length of these displacements follows power-law probability density function P(xi) ~ xi-μ, where xi is the move length (displacement of consistent direction) and μ represents the power-law exponent, which is 1 < μ 3. There is a debate whether the pattern is induced by the internal factors or the external factors [4,5]
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