LAUSR

When allogeneic plasmodia of Myxomycetes encounter each other, they fuse or avoid each other depending on the combination, indicating that plasmodia can recognize self and non-self. The mechanisms of allorecognition are not fully understood from the perspective of behavior. In the present study design, Physarum rigidum geographical strains naturally encountered each other with the aim of formulating a model of allorecognition behavior. The plasmodia of P. rigidum can recognize each other by touching the cell membrane surface. However, contact is not necessary. Cases involving the absence of contact occur by the slime sheath of hyaline mucus that covers plasmodium. This so-called non-contact allorecognition has distinct characteristics regardless of distance and is faster compared to that involving contact. These facts suggest that the plasmodia of one P. rigidum can recognize others and can rapidly and safely decide whether to avoid or fuse with other plasmodia, using the non-contact allorecognition. Previous studies on P. polycephalum have regarded the slime sheath as a repellent or as an external memory for self. These studies advocated that the principle of the plasmodium is basically avoidance of other individuals. In this study, we propose the self-extension model based on data of the allorecognition behavior of P. rigidum. According to the model, the slime sheath functions as a signal that disperses information about self into the environment. Self-extension by the slime sheath enables non-contact allorecognition.