How a single cell slime mold makes smart decisions without a central nervous system
From:
Technical University of Munich (TUM)
February 23, 2021 -- Researchers have
identified how the slime mold Physarum polycephalum saves memories -- although
it has no nervous system.
Having a memory of past events enables
us to take smarter decisions about the future. Researchers at the Max-Planck
Institute for Dynamics and Self-Organization (MPI-DS) and the Technical
University of Munich (TUM) have now identified how the slime mold Physarum
polycephalum saves memories -- although it has no nervous system.
The ability to store and recover
information gives an organism a clear advantage when searching for food or
avoiding harmful environments. Traditionally it has been attributed to organisms
that have a nervous system.
A new study authored by Mirna Kramar
(MPI-DS) and Prof. Karen Alim (TUM and MPI-DS) challenges this view by
uncovering the surprising abilities of a highly dynamic, single-celled organism
to store and retrieve information about its environment.
Window into the past
The slime mold Physarum
polycephalum has been puzzling researchers for many decades. Existing
at the crossroads between the kingdoms of animals, plants and fungi, this
unique organism provides insight into the early evolutionary history of
eukaryotes -- to which also humans belong.
Its body is a giant single cell made up
of interconnected tubes that form intricate networks. This single amoeba-like
cell may stretch several centimeters or even meters, featuring as the largest
cell on earth in the Guinness Book of World Records.
Decision making on the most basic levels
of life
The striking abilities of the slime mold
to solve complex problems, such as finding the shortest path through a maze,
earned it the attribute "intelligent." It intrigued the research
community and kindled questions about decision making on the most basic levels
of life.
The decision-making ability of Physarum
is especially fascinating given that its tubular network constantly undergoes
fast reorganization -- growing and disintegrating its tubes -- while completely
lacking an organizing center.
The researchers discovered that the
organism weaves memories of food encounters directly into the architecture of
the network-like body and uses the stored information when making future
decisions.
The network architecture as a memory of
the past
"It is very exciting when a project
develops from a simple experimental observation," says Karen Alim, head of
the Biological Physics and Morphogenesis group at the MPI-DS and professor on
Theory of Biological Networks at the Technical University of Munich.
When the researchers followed the
migration and feeding process of the organism and observed a distinct imprint
of a food source on the pattern of thicker and thinner tubes of the network
long after feeding.
"Given P. polycephalum's
highly dynamic network reorganization, the persistence of this imprint sparked
the idea that the network architecture itself could serve as memory of the
past," says Karen Alim. However, they first needed to explain the
mechanism behind the imprint formation.
Decisions are guided by memories
For this purpose the researchers
combined microscopic observations of the adaption of the tubular network with
theoretical modeling. An encounter with food triggers the release of a chemical
that travels from the location where food was found throughout the organism and
softens the tubes in the network, making the whole organism reorient its
migration towards the food.
"The gradual softening is where the
existing imprints of previous food sources come into play and where information
is stored and retrieved," says first author Mirna Kramar. "Past
feeding events are embedded in the hierarchy of tube diameters, specifically in
the arrangement of thick and thin tubes in the network."
"For the softening chemical that is
now transported, the thick tubes in the network act as highways in traffic
networks, enabling quick transport across the whole organism," adds Mirna
Kramar. "Previous encounters imprinted in the network architecture thus
weigh into the decision about the future direction of migration."
Design based on universal principles
"Given the simplicity of this
living network, the ability of Physarum to form memories is intriguing. It is
remarkable that the organism relies on such a simple mechanism and yet controls
it in such a fine-tuned manner," says Karen Alim.
"These results present an important
piece of the puzzle in understanding the behavior of this ancient organism and
at the same time points to universal principles underlying behavior. We
envision potential applications of our findings in designing smart materials
and building soft robots that navigate through complex environments,"
concludes Karen Alim.
https://www.sciencedaily.com/releases/2021/02/210223121643.htm
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