Learning in unicellular organisms

Learning is without doubt one of the key innovations of evolution. Only learning allows inclusion of past experiences in optimal decisions in a fluctuating environment. Recent research shows that the basic principles of learning processes are manifested much earlier in the evolution than assumed previously. Usually learning is attributed to organisms with nervous systems, but research of slime molds demonstrated that certain types of learning are already present in unicellular life forms. In this project a behavioral ecologist, a molecular ecologist and two physicians work together to observe early forms of learning and to understand the underlying principles. Slime molds will be exposed to certain triggers and their responses will be studied to estimate the time span of memory as well as the possibility of associative learning. In addition the potential mechanisms will be studied by modelling approaches and by analyses of the role of DNA modifications. Finally the impact of learning on fitness and evolutionary success will be evaluated. By employing a multidisciplinary approach with primitive organisms, we will develop a holistic concept of learning and cognition.

Learning, as a complex phenomenon, is usually attributed the neuronal multicellular organisms. Research has shown that phenomena, which are reminiscent of learning and often called habituation, are present also in non-neural organisms and even observed in unicellular organisms. The project focused on possible mechanisms of unicellular learning in slime molds. We consider habituation in slime molds as a complex phenomenon, which does not rely on a single mechanism, but is characterized by the interaction of multiple factors acting on different levels. We consider biomechanics as a prime factor influencing the growth habit of slime molds and the involved flow phenomena through the network-like organism. Most importantly, we consider the physical properties of the slime excretions important for the formation of veins and the arrangement of contractile elements within the veins. The vein thickness hierarchy and internal structure of the veins encode past experiences, which can be interpreted as a memory. This kind of memory is dynamic and can change over time, due to the physical properties of the slime coating. We also argue that the flow patterns established by the details of the network architecture create feed back to the transcriptomic profiles, which may explain the differences observed in spatial transcriptomics. To summarize, we found that the phenomenon of memory formation is triggered by mechanic mechanisms in this unicellular organism.