Spektrale Phototaxis von Planktonrotatorien

The effect of light, dark or altered circadian cycle on the lifespan of the rotifer Asplanchna brightwelli

Rotifers were maintained in various light conditions for at least 20 generations. In the first set of experiments lifespan and fecundity data were compared for groups of rotifers maintained under LL (continuous light), DD (continuous dark) or LD 12:12 (control, 12 hr. light 12 hr. dark). The mean lifespan of the rotifers cultured in DD conditions was significantly increased as compared to the LL or LD 12:12 groups but there were no fecundity differences. There was no alteration in lifespan or fecundity of the LL group as compared to the LD 12:12 control. In a second set of experiments, an LD 6:18 cycle was imposed to determine whether a shift in the circadian cycle would influence lifespan. Rotifers exposed to the LD 6:18 cycle and to the DD conditions showed an 18% and 22% increase in mean lifespan respectively. The results are interpreted to demonstrate that lifespan is influenced by the circadian cycle.

Do Rotifers show "avoidance of the shore"?

The term "avoidance of shore" was used in literature to describe the observation that pelagic crustacea are in general absent near the shore. Experiments in the field show, that Rotifers-which form, together with crustaceans, the main mass of zooplankton-can also be divided not only by morphological criteria but also as a result of their horizontal distribution into inhabitants of either the littoral or the pelagic zone of a lake.These differences of horizontal distribution can be explained by a typical behavioral difference between the littoral rotifer Euchlanis dilatata and the pelagic Asplanchna priodonta: when exposed in the shore zone, Asplanchna wanders in the direction of the pelagic zone, while Euchlanis on the contrary does not prefer any particular direction under the same conditions. Experiments at different lakes with other pelagic rotifers confirm that the "avoidance of shore" shown by Asplanchna is a general phenomenon.The influence of the analyzed behavior on the horizontal distribution patterns of rotifers and the factors which cause and determine the direction of the migration are discussed.