Influence of accelerations on the spatial orientation of Loxodes and Paramecium

The gravitactic ciliates Paramecium and Loxodes were cultivated for 15 days in space during the IML-2 spacelab mission. At dedicated times their behavioral responses to different accelerations between 10(-3) x g and 1.5 x g were investigated by using a slow rotating centrifuge microscope (NIZEMI). The threshold for gravitaxis of Paramecium was found to be at > 0.16 x g and < or = 0.3 x g. No adaptation of Paramecium to the conditions of weightlessness was observed over the duration of 15 days. Loxodes showed no graviresponses to increasing accelerations, though it demonstrated gravitaxis after return to earth.