SPECIFIC BEHAVIORAL-RESPONSES TRIGGERED BY IDENTIFIED MECHANOSENSORY RECEPTOR-CELLS IN THE APICAL FIELD OF THE GIANT ROTIFER ASPLANCHNA-SIEBOLDI

The giant rotifer Asplanchna sieboldi swims by the propulsive effect o f thousands of cilia arrayed in clusters around the apical field, whic h has several mechanosensory structures (sensilla) located at defined positions. Males and females differ in both their patterns of behaviou r and their sensory receptor equipment. Unstimulated males swim straig ht with occasional spontaneous changes in direction until they hit an obstacle with their apical field. Depending on the direction and the s trength of the mechanical interference, the animals show different beh avioural responses. To analyse the effect of excitation of the apical mechanosensitive sensilla on these responses, males were held on micro capillaries, and the sensitivity of individual sensilla was assayed us ing micromanipulator-mediated mechanical stimulation. Stimulation of e ach of the four different types of sensillum triggered a specific and well-defined initial behavioural response. Individual animals behaved identically with respect to the receptor specificity of the responses. The behaviour of free-swimming males upon contact with obstacles or f emales is discussed on the basis of these results.