Bräucker R, Machemer-Röhnisch S, Machemer H, Murakami A (1992) Gravity-controlled gliding velocity inLoxodes


The locomotion of Loxodes as controlled by the natural gravity vector was investigated employing a mass-cell approach. Samples of cells were incubated for 4 hours in a 1.6 mm deep well (41 x 85 mm) filled with defined experimental solution. Their gliding locomotion on surfaces inclined between 0° and 90° was recorded by videocamera. Steady gliding rates (median of total: 206 µm/s; n = 12711) were evaluated by calculating the vertical component from observed tracks. At a given inclination the rates of downward and upward gliding were similar. The sedimentation rate of freely suspended nickel-immobilized specimens (S = 49 µm/s), and vertical rates of displacement at 6 differently inclined planes, and with cells in "sitting" posture as well as "hanging" (upside down), were used to determine the gravity-dependent component (delta = -49 µm/s) during gliding motion. Numerical equality of the gravity force to produce S and of the counterforce to produce delta follows from the observed constancy of gliding rates and identical medians of vertical locomotion up and down (169 µm/s). It is concluded that neutralization of sedimentation is a precondition for Loxodes to migrate along a vertical O2 gradient in its freshwater habitat.