Symbolic Analysis of Plankton Swimming Trajectories: Case Study of Strobilidium sp. (Protista) Helical Walking under Various Food Conditions

Abstract

The swimming behavior of the ciliate Strobilidium sp. was recorded using cinematographic techniques. A density of 20 ciliates/ml was used under 4 experimental food conditions: 121, 625, 3025, and 15,125 cells/ml of the dinoflagellate Gymnodinium sp. In total, 100 trajectories per experiment were recorded and analyzed. We classified this ciliate’s swimming trajectories into categories we called “helix”, “non-helix”, and “break”. These swimming states were identified using automated recognition of helices, based on values of swimming trajectory angles. We performed a symbolic analysis of the succession of swimming states which enabled discrimination between food concentration experiments, and provided a more-complete characterization of the swimming behavior. We found that helical swimming patterns first increased with food concentration then decreased with a corresponding increase in the numbers of breaks. Non-helical motions were related to high food concentrations. We further used these results to simulate a ciliate’s trajectories using a symbolic dynamic model to generate a sequence series. Helices were reconstructed using a model with 2 inputs: amplitude and period. This study shows that a methodology developed to describe copepod behavior can also be applied to characterize and simulate ciliate helical and non-helical swimming dynamics.