Complex population dynamics in a spatial microbial ecosystem with Physarum polycephalum

Abstract

This research addresses the interactions between the unicellular slime mold Physarum polycephalum and a red yeast in a spatial ecosystem over week-long imaging experiments. An inverse relationship between the growth rates of both species is shown, where P. polycephalum has positive growth when the red yeast has a negative growth rate and vice versa. The data also captures successional/oscillatory dynamics between both species. An advanced image analysis methodology for semantic segmentation is used to quantify population density over time, for all components of the ecosystem. We suggest that P. polycephalum is capable of exhibiting a sustainable feeding strategy by depositing a nutritive slime trail, allowing yeast to serve as a periodic food source. This opens a new direction of P. polycephalum research, where the population dynamics of spatial ecosystems can be readily quantified and complex ecological dynamics can be studied..

The Principle of Dynamic Holism: Guiding Methodology for Investigating Cognition in Nonneuronal Organisms

“…The question arises, however, as to where and when a P. polycephalum should migrate in a given area to optimize the number of consumable microorganisms that grow on its extracellular slime later. This is a decision-making problem, and some support as to what kind of decision P. polycephalum is making can be gleaned from Epstein et al (2021, 9):We speculate that as P. polycephalum navigates its environment it occupies specific regions of a morphospace so that it may build a spatiotemporally optimal slime sheath to farm the most microorganisms.…”

“…However, from the perspective of Reid et al’s (2012) results and the hypothesis that their results support, navigational decisions for optimal foraging are made primarily on the basis of the spatial distribution of extracellular slime. When considered in light of the results of Epstein and colleagues’ (2021) experiment—results they obtained, I suggest, by implicitly deploying something like PDH—Reid et al’s (2012) explanation is accurate but may be also incomplete: it stops short of capturing important aspects of the kind of nuanced decision-making that drives P. polycephalum ’s navigational behavior. The importance of using PDH-guided investigation to complement experiments from which the kind of ecological variables found in an organism’s niche are abstracted away is made explicit when considering the difficulty of inferring the complex kind of navigational decision-making that occurs in Epstein et al’s (2021) experiment strictly from the kind of externalized navigational memory use that is supported by Reid et al’s (2012) experiment.…”

“…These researchers demonstrated that P. polycephalum in fact avoids biochemical cues diffuse in the substrate and presumably present in extracellular slime that has been produced by other conspecifics when those conspecifics have undergone stress (starvation); slime trails, on the other hand, left by nonstressed (well-nourished) P. polycephalum are not avoided but, instead, can act as attractants given the cues they contain. Taking both Reid et al’s (2012) and Briard et al’s (2020) results into consideration, Epstein et al (2021) formulated a novel hypothesis based on the following observations and considerations: P. polycephalum , as it migrates across surfaces in the wild, regularly preys on red yeast (and other microorganisms); the extracellular slime deposited at those sites at which it has consumed more red yeast tends to be more attractive to it than the slime at other sites where it or its conspecifics consumed no nutrients—the condition of the extracellular slime at the former sites chemically reflecting the well-nourished state of the P. polycephalum that produced it. If the deposited extracellular slime also provides a source of nutrients for a subsequent colony of growing red yeast, and if they do not consume all the slime, then the site of slime deposition might attract the P. polycephalum back to the newly grown yeast.…”

“…Using advanced image technology to capture the population dynamics between P. polycephalum and red yeast that were introduced to the same dishes, Epstein et al (2021) were able to detect an inverse growth relationship between the two organisms, suggesting a predator–prey relationship and, indeed, oscillatory successional dynamics 14 . At first blush, this result may not strike one as relevant to the expression of any cognitive capacity.…”

“…These results and those of Briard et al (2020), however, complicate the picture in showing that slime trails are not merely cues for avoidance navigation; depending on the condition of the P. polycephalum that deposited the trail and hence the chemical makeup of the trail, they can also be attractants. Epstein et al’s (2021) results may suggest that what makes the extracellular slime an attractant later may be the presence of microorganisms that are more likely to grow on slime that was produced by a less-stressed P. polycephalum 15 . The question arises, however, as to where and when a P. polycephalum should migrate in a given area to optimize the number of consumable microorganisms that grow on its extracellular slime later.…”