Flight control during ‘free yaw turns’ inDrosophila melanogaster

Summary

• 1. A new method for studying flight control in flies is introduced. In this set-up (thread paradigm) the fly is free to rotate around its vertical body axis but is otherwise kept stationary. The fly's orientation is continuously monitored optoelectronically. For statistical evaluation flight traces are divided into ‘turns’ (summed successive angular displacements until the direction of turning changes).

• 2. In the thread paradigm flies perform quick turning maneuvers corresponding to torque spikes at the torque compensator and to body saccades in free flight. In between, flies maintain a rather straight course. This obvious observation is reflected in bimodal velocity and turn histograms, both of which are composed approximately of a Gaussian and an exponential distribution.

• 3. The frequency of body saccades declines exponentially (decline constant 0.026/°), angular peak velocities increase linearly (12.5(°/s)/°=12.5/s), and the duration of saccades saturates (at about 250 ms) with increasing size of saccade. After a quick rising phase (40–60 ms) body saccades show, as a mean, an exponential drop of angular velocity with a time constant of about 40 ms.

• 4. The pattern dependency of the turning behavior resembles that measured using the torque compensator. The size of body saccades is influenced by the visual pattern wavelength. The direction of a body saccade may depend on that of the preceding one thus revealing its special status as part of a larger behavioral sequence.

• 5. Experiments with constant torque bias reveal an internal reference of zero torque. Corresponding measurements using the torque compensator suggest an efficacy model to be applicable in characterizing torque traces with constant rotatory bias. This new model allows simulation of constant-bias torque traces by applying a single efficacy factor to no-bias torque traces.