Graviresponses of Gliding and Swimming Loxodes Using Step Transition to Weightlessness

Cells of Loxodes striatus were adjusted to defined culturing, experimental solution, O2‐supply, temperature, and state of equilibration to be subjected to step‐type transition of acceleration from normal gravity (1 g) to the weightless condition (μg) during free fall in a 500‐m drop shaft. Cellular locomotion inside a vertical experimental chamber was recorded preceding transition and during 10 s of μg. Cell tracks from video records were used to separate cells gliding along a solid surface from free swimmers, and to determine gravitaxis and gravikinesis of gliding and swimming cells. With O2 concentrations ≥ 40% air saturation, gliders and swimmers showed a positive gravitaxis. In μg gravitaxis of gliders relaxed within 5 s, whereas gravitaxis relaxation of swimmers was not completed even after 10 s. Rates of horizontal gliders (319 μm/s) exceeded those of horizontal swimmers (275 μm/s). Relaxation of gravikinesis was incomplete after 10 s of μg. Analysis of the locomotion rates during the g‐step transition revealed that gliders sediment more slowly than swimmers (14 versus 45 μm/s). The gravikinesis of gliders cancelled sedimentation effects during upward and downward locomotion tending to maintain cells at a predetermined level inside sediments of a freshwater habitat. At ≥ 40% air saturation, gravikinesis of swimmers augmented the speed of the majority of cells during gravitaxis, which favours fast vertical migrations of Loxodes.