We take for granted that we can remember where the biscuits are kept in our cupboard.
We have a brain and somewhere this stores information in the form of memories
that we can access to help us find those all important biscuits.
But our body and brain are complex systems built of thousands if not millions of cells
working together. How is it possible that one of the simplest organisms
consisting of only a single cell can somehow work together and store memories that it can access?
A new study published in the journal Proceedings of the National Academy of sciences, investigates
how giant slime molds encode memories in response to food sources. Let explore what they discovered.
In the study the scientist observed a slime mold in a laboratory setting and used this
to generate a theoretical model. Using both of these they were able to determine that
changes in the organisms tubes happened in response to a newly introduced food source.
They were able to determine that it took the slime 45 minutes to reorganise its entire network of
tubes to face the new food source. It then took another 45 minutes for the mold to start moving
towards the food source. After 310 minutes the slime had fully engulfed the food source.
When they then remove part of the slime mold to make it smaller
the mold now would reorganise itself in only 15 minutes
and would begin moving towards the food source a further 30 minutes later.
This study showed that slime molds are capable of making decisions within 10 to 20 minutes.
What drives this decision process is unclear. It appears as if the slime mold is able to achieve
this through the encoding of the location of the food source via the network of tubes.
The scientist set out to test this exact idea. They used their simulation to show how an
agent from the food source likely entered the slime mold’s tubes. They used a softening agent
near the food to cause the tubes near the food source to expand and dilate.
These dilated tubes then imprinted the memory of the nutrient source
in its network. More remarkable is that it appears that this isn’t a one time response.
Rather the slime mold has ‘irretrievably changed’ the flow patterns of its tubes.
And this is a sign of long term memory function.
The study found that slime molds encode memories of nutrient sources within their
tubes. The tubes that survive the longest are those directly
bearing the memory of the nutrient stimulus that lead to their growth
Hence, memories stored in the hierarchy of tubes diameters, and particularly in the location of
thick tubes, are subsequently layered on top of each other, with every new stimulus differentially
reinforcing and weakening existing thick tubes in superpositions of existing memories.
So why is this a big deal? Previously we had assumed that only creatures with
e central nervous system were capable of memories.
Creatures like this slime mold do not have this so should not be able to store any memories.
In most animals, memory typically forms as a result of synaptic plasticity, this essentially
means the brain makes connections across specific neuronal networks that are strengthened over time.
This study shows that the a similar mechanisms can be achieved in the tube networks of slime molds.
Memory function is normally reserved for only higher level organisms.
This research suggest that even the simplest lifeforms have memory.
Fungi like this slime mold play a vital role in sustaining the eco system of trees.
This is very obvious when you examine the remarkable story of the zombie trees.
Normally plants use their leaves to make food from the Sun’s energy and carbon dioxide. With
the exception of a very few parasitic plants no tree is known to grow without green foliage. Some
can however end up as zombie trees. This happens when they lose all their leaves and large parts of
their trunk. Often they die but every now and then the trees are kept alive by their surroundings.
This has been something that has been observed for almost 200 years
but the evolutionary and physiological processes leading to their existence
remains a mystery. This is partly because they are so rare and whatever happens on
their journey from feeding themselves to being fed happens out of sight… likely below ground.
It has already been shown that trees send each other signals through a network of
fungi buried among their roots. These signals can include communications about environmental
changes and the transfer of nutrients to neighbouring trees before they die.
Ecologist Suzanne Simard suggests that this supply
can continue beyond the apparent death of an individual tree.
She measured the water flow in the stem of a living tree stump and its neighbouring tree and
showed an underground connections was likely responsible for the survival of the stump.
If forests feature interconnected root networks where water, carbon and nutrients are exchanged,
this would be equivalent to power, water and gas grids supplying a city.
There is evidence that shaded trees are supported by non-shaded trees
and the fact that zombie trees are still supplied with resources
gives rise to the much bigger idea that forests act and survive as a whole.
As if these stories were not remarkable enough I would like to end by looking at a recent study
that seemed to demonstrate that flowers are able to sense the buzzing of a nearby bee
and can temporarily increase the concentration of sugar in their flowers nectar.
This means that the flower itself is acting like ears which are tuned into the specific frequency
of a bees wings and yet can tune out irrelevant sounds that might be created by the wind.
As the researchers looked at how sound works and specifically their relationship with flowers they
realised that the shape and size of the flower tend to be concave or bowl shaped.
This makes them perfect for receiving and amplifying sound waves.
When they examined the shape of the flower they discovered that it would resonate
at the specific frequencies created by a bee.
To test their idea they then started to remove some of the petals
and discovered that these would fail to resonate at the required frequencies.
This concept of plants hearing opens up many new questions and also links
back to the idea that trees and plants in forrest
communicate with each other. Could they sense other herbivores nearby and warn their neighbours.
Maybe they could also generate sounds that attract animals involved in dispersing that plants seeds?