Dynamic patterns in the locomotion and feeding behaviors by the placozoan Trichoplax adhaerence

The placozoan Trichoplax adhaerence is one of the most primitive multi-cell ular organisms, and moves about accompanying perpetual changes in its shape . Changes in position, locomotion velocity and the outer shape of the organ ism were monitored quantitatively with use of a computer image analysis, an d their dynamic patterns in free locomotion and upon feeding were analyzed in terms of non-linear dynamics. The organism changed its behavioral patter ns discontinuously in response to various concentrations of yeast extracts (food). (1) At low concentrations, the organism moved fast with perpetual r andom changes in shape. Both locomotion velocity and shape changes exhibite d 1/f fluctuations. (2) At high concentrations, the shape of the organism a s well as the locomotion exhibited oscillations with periods of about 8 min . These limit cycle oscillations bifurcated into the period 2 at the highes t concentration tested. The organism flattened more strongly and the locomo tion was more reduced on the whole at higher concentrations. (3) At the int ermediate concentrations, two patterns as monitored above appeared: one pat tern continued for a while and switched to the other abruptly. (4) The aver age square displacement of the organism increased linearly with time in all cases, indicating that the locomotion is a Brownian movement. In this way, the feeding behaviors by the placozoan are organized as successive co-oper ative transitions among non-linear dynamic states. (C) 1999 Elsevier Scienc e Ireland Ltd. All rights reserved.