Gravity-controlled gliding velocity in Loxodes

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 × 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 components 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 with cells in "sitting" posture as well as 'hanging' (upside down) were used to determine the gravity-dependent component (Δ = - 49 μm/s) during gliding motion. Numerical equality of the gravity force to produce S and of the counterforce to produce Δ follows from the observed constancy of gliding rates (V) and identical medians of vertical displacements during gliding along vertically oriented surfaces (169 μm/s). It is suggested that neutralization of sedimentation might be a favourable condition for migration and accumulation of Loxodes along vertical O(2) gradients in its freshwater habitat.