Revisiting Chirality in Slime Mold: On the Emergence and Absence of Lateralized Movement in Physarum polycephalum Influenced by Various Stimuli

Behavioral lateralization in animals is a well-known phenomenon; however, it has only rarely been studied in unicellular organisms. A groundbreaking study found lateralized movement in T-mazes in the formless plasmodia of the slime mold Physarum polycephalum. In this work, a replication of that study was conducted in a specially designed, elaborated T-maze system. Considering the amoeboid organism’s diverse sensory capabilities, we further comprehensively investigated the influence of light, artificial magnetic fields, the magnetic field of the Earth, and vibration on movement direction. Two different clonal lines were tested to assess genetic diversity, encompassing over 1600 individual plasmodia. Our results show that no general lateralized behavior exists in the absence of stimuli in both clonal lines. On the other hand, Physarum’s sensitivity to strong magnetic fields and vibration induces significant true lateralization in previously nonlateralized plasmodia (37.6% right and 62.4% left, respectively). Possible mechanisms behind this induced lateralization are discussed. We conclude that previous findings showing lateralization are likely to have been influenced by unknown external stimuli.