[Diurnal rythm of locomotor activity in Admetus pumilio C. Koch (Arach., Amblypygi) from the neotropical rain forest. II].

The locomotor activity of the exclusively dark-active species Admetus pumilio shows a bigeminal type of diurnal rhythm, modified by an interposed third peak of activity. In accordance with Aschoff's rule, the period length depends on light intensity and is shortened in DD. The phase-angle difference must be determined separately for each form of activity. The first movements at the resting place ("awakening") and departure from it are the most readily identifiable forms of activity. Awakening takes place earlier and earlier with decreasing light intensity, thus diverging from departure more and more.Differing degrees of activity in LL and LD of different intensities show that light stimulates or inhibits depending on its intensity. The turning point between the two effects lies between 10(-2) and 10(-3) lx. Below this limit differences in light intensity are not discerned, although LL is well discerned from LD.Diurnal temperature cycles with amplitudes up to 8° C are unable to synchronize the circadian rhythm of Admetus, but may have a strongly masking effect. Different levels of constant temperatures influence the phase-angle differences, which become increasingly positive with rising temperature. Activity also increases with temperature, but decreases in the extra-optimal range above approximately 30° C. The L-phase/D-phase ratio of activity shows a maximum at about 26° C.In Admetus the dependence of activity parameters upon light intensity is unidirectional and shows no optima. In contrast to the findings by Erkert (1967) is discussed that optima are only realized in dusk active animals and are lacking in day-active and night-active species.