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Abstract:
Visual motion processing enables moving fruit flies to stabilize their course and altitude and to approach selected objects. Earlier attempts
to identify task-specific pathways between two photoreceptor systems (R1-6,
R7+8) and three steering parameters (wingstroke asymmetry, abdomen
deflection, hindleg deflection) attributed course control and object
fixation to R1-6 mediated simultaneous reactions of these parameters. The
present investigation includes first results from fixed flying or freely
walking ninaE17 mutants which cannot synthesize the R1-6
photoreceptor-specific opsin. Retention of about 12 percent of the normal
course control and about 58 percent of the object fixation in these flies
suggests partial input sharing for both responses and, possibly, a
specialization for large-field (R1-6) and small-field (R7+8) motion. Such
signals must be combined to perceive relative motion between an object and
its background. The combining links found in larger species might explain a
previously neglected interdependence of course control and object fixation
in Drosophila. Output decomposition revealed an unexpected orchestration of
steering. Wingstroke asymmetry and abdomen deflection do not contribute in
fixed proportions to the yaw torque of the flight system. Different steering
modes seem to be selected according to their actual efficiency under
closed-loop conditions and to the degree of intended turning. An easy
experimental access to abdominal steering is introduced.
