Experience shapes future foraging decisions in a brainless organism

Abstract

The ability to change one’s behaviour based on past experience has obvious fitness benefits. Drawing from past experience requires some kind of information storage and retrieval. The acellular slime mould Physarum polycephalum has previously been shown to use stored information about negative stimuli. Here, we repeatedly exposed the slime mould to three stimuli with differing levels of potential risk: light, salt and lavender. We asked if the slime mould would change its foraging behaviour depending on the level of risk. In our experiment, taking risk yielded better food. We consistently selected individuals that made the same foraging decision (accepting risk or avoiding risk) over multiple trials. Hence, the same individuals were tested over a period of time, but only individuals that continued to make the same decision were allowed to continue. Regardless of selection regime, slime moulds in the light became more likely to select the food in the light over time, while those exposed to salt became more salt averse. Lavender had no effect. Our results can cautiously be interpreted as examples of non-associative learning, adding to a growing body of work showing that the absence of a central nervous system is no impediment to possessing sophisticated information processing.

Thoughts from the forest floor: a review of cognition in the slime mould Physarum polycephalum

“…A later study provided supporting evidence that the mechanism underlying habituation, and its transferability between plasmodia, is high levels of the repellent stimulus itself (in this case NaCl salt) being taken up into the cell and distributed throughout the protoplasm as a ‘circulating memory’ (Boussard et al 2021 ). By contrast, Smith-Ferguson and colleagues ( 2022 ) found the opposite result in a study published a year later. Plasmodia repeatedly exposed to NaCl were more likely to avoid the salt.…”

“…This success certainly favours Physarum as a non-neural system that has the potential to demonstrate associative learning, but this is far from a foregone conclusion. Smith-Ferguson and colleagues ( 2022 ) conclude—probably correctly, given the bias against publication of negative results—that a number of attempts to show associative learning in a wide range of organisms have probably failed. If so, that raises a question: why?…”

The Multiple Realizability of Sentience in Living Systems and Beyond

“…But what if the same mental activities and states can be similarly achieved by information processing within other substrates? The generalizability of cognition is strongly evidenced by observations that non-neural systems can anticipate reinforcements (Rodríguez and Garzón, 2010), avoid conditioned stimuli (Smith-Ferguson et al, 2022), switch between cooperative and competitive strategies as a function of kinship and resource availability (Novoplansky, 2009), and even display mimicry (Roy, 1993;Ngugi and Scherm, 2006;Schaefer and Ruxton, 2009;Frank, 2019).…”