The Effect of the Shape of the Environment on the Reactions of P. Polycephalum to Food

8/2/2019 The Effect of the Shape of the Environment on the Reactions of P. Polycephalum to Food

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The Effect of the Shape of the

Environment on the Reactions of P.

Polycephalum to Food

Researched and written by Jacob Van Buren, and Teo Fleming

Biology 1 Acc: Panagakis, period 6

Due: Monday, May 9, 2011


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IntroductionPhysarum Polycephalum (commonly referred to as Slime Mold / Mould) is

classified under the Kingdom Amoebozoa and, in its plasmodial stage, is an

acellular membrane containing many nuclei that function together as one

organism. However, if conditions are unfavorable, it can turn into the

sclerotium form of its life cycle, which is a resistant, dormant-like state from

which a specimen can be recovered with no harm done. It is commonly found

in the southern US, in shady, wooded areas. P. Polycephalum thrives in cool,

dim, and moist environments, and feeds on simple sugars, microorganisms,

and some yeasts by phagocytosis. P. polycephalum tends to avoid light (Latty,

Beekman), and in its presence grows more slowly. If there are other conditions

pertaining, then it may undergo sporulation. In sporulation, sacs of fruiting

bodies are created by meiosis, which, in turn creates haploid nuclei, which

are packed as spores (Genomes | Physarum Polycephalum).

This Experiment was designed to test the effect of the shape of the

environment on the reactions of Physarum Polycephalum to food. It involved

placing 30 specimens on non-nutrient agar Petri dishes. They were then

photographed while they grew toward their objectives. The photos were then

used to create measurements of the mold to find out how far it was in relationto the food sources that served as its objectives.

Our prediction is that if P. Polycephalum is put in an environment in

which it is separated from its food by a maze, it will be able to figure its

environment out and find its way to the food with ease and efficiency. We

believe this will happen because the mold is attracted to the minute traces of

chemicals that food releases that make up the objects smell.

PHYSARUM is

the singular aroma of a cool damp forest

the vibrant yellow of a saucy lemon

the relentless [rhythms] of nature's multiple cycles

the storehouse of countless answers

the tantalizing challenge that lures us on (Namleda)


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MethodologyIn this experiment, 30 different Petri dishes were set up with a

moisturized Physarum Polycephalum sclerotium fragment, measuring an

average of about 1mm2. First, we cut out the pieces of the sclerotium and put

one in the center of each Petri dish. Three oats (included with slime mold)

were then placed in the Petri dish, as equidistant as possible from each other

(see figure 4). If the dish was part of an experimental group, the maze was

preconstructed and soaked in bleach and rinsed to sterilize it. The Petri dishes

were put inside of plastic pie containers, with 2-3 Petri dishes in each pie

container. A moist paper towel was placed over the top of the container,

keeping the mold moisturized and allowing it to grow. (see figures 5 & 6)

The container lids were kept above the base of the container by some

cut pieces of rubber tubing that were places at 4 places along the rim of the

lid. The lids were then placed on top, and photos are taken from the bottom,

with significant light coming from behind the images. Using this method, we

were able to track the mold's growth even though there were several layers ofclear material between the experimenter and the mold.

Although a deep affection was felt for the mold by all involved, the

dishes' names were not based on any personality or physical traits. Instead,

they were based on which container and group they were in. Labels were used

to keep track of these names and to minimize the chance of switching dishes.

HypothesisIf P. Polycephalum is put in an environment in which it is separated from

its food by a maze of a certain degree of complexity, it will not be affected in

any significant way in reaching its objective.


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Analysis and Conclusion

In doing our experiment, we found that as the complexity of the

environment around the mold increased, so did the time that it took the mold

to reach the oats. In the control group and variable groups, the oats were the

same distance away from the mold as the bird flies, but not as the mold

moves. The slime mold is an amazing organism and is able to use logic to

grow, and determine where food is. In our experiment, we explored the

different methods the mold employs to find food, as well as their efficiencies.

In the experiment, there were 3 groups: one for control with no

environmental changes to the average Petri dish, and two other dishes with a

maze built solely out of Lego. This maze was meant to test the slime molds

ability to find food even when confronted with a difficulty such as a hostile

environmental shape. To get a better understanding of the two mazes used,

see Figure 5 and Figure 6. The Control group was exactly like these two groups

but without the maze. In the three graphs provided, one can witness for

themselves how efficient the mold was when confronted with an obstacle

compared with the control group.

Graph 1 shows the distance from the center oat. This is the measure of

the center oat to the furthest instance of mold from the center oat. Using this

measurement, we can gauge how far out the mold traveled in search of food.

The graph shows that the Control group traveled the furthest fastest, but the

Variable groups were not far behind. Group Y faltered from minute 3000 to

minute 5000; however it was able to still search farther than Group B nearer to

the end of the experiment. This graph overall shows that even though the

mold will falter for a few hours if confronted with an obstacle, it will almost

always get back up and continue its search without pause.Graph 2 shows the distance from the outer oats. This is the measure

from the outer oats to the nearest instance of slime mold. This graph allows us

to gauge how quickly the mold was able to get to the food and nourish itself.

For Groups C and Y, the average distance was used, as there was no forced

preference between one oat and another. However, for Group B, the two oats


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needed to be graphed separately because there was a forced preference for

one oat. We thus named the first oat that the mold would encounter oat 1 and

the second oat 2. When looking at the graph, one can see that Group C got to

the oats much more quickly than the other groups. One would expect to see

the mold reaching oat 1 in Group B first, however that is not the case. This is

possibly due to several of the reasons mentioned below as well as the data

collecting methods used. Group Y had serious trouble getting to both oats,

possibly because the large Lego brick prevented it from detecting that there

was an oat to be found just past the brick.

Graph 3 is a combination of all growth, taking into account all three

measurements. Group C is obviously the winner in this category, and stays

ahead of the other two groups for the duration of the experiment. In fact, it

most likely would have continued growing and would not have leveled off had

it not reached the side of the Petri dish and had no where else to go. In fact,

when cleaning up, it was discovered that several dishes in Group C mold had

made their way onto the paper towel providing it with moisture and had grown

all around the containers edge. Unfortunately, no good pictures document this

phenomenon as the camera was not handy at the time of discovery. Group B

was not too far behind the control group and in fact, other than a fewstumbles, kept up relatively well considering it had a maze to deal with. The

same is not true for Group Y which fell far behind for the middle of the

experiment. This is most likely because the maze did not allow the mold to

sense the oats which lay just beyond the walls.

Our experiment showed that the mold usually found a relatively close to

optimal solution. We believe that the mold did this by employing a simple

evolutionary tactic. At first, the mold fans out in all directions, possibly guided

by chemical receptors in the membrane. (Figure 4) The mold then is attracted

to those stimulants that it detects in the oat. The stimulant promotes growth

on that part of the mold, giving it a net growth towards the source of the

stimulant. Once the mold finds a way to the oat, that part of the mold is


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supplied with nutrients, which it shares and distributes throughout the

organism.

Given that the mold supplies all parts of itself with at least some amount

of food, and the amount of food that is supplied decreases proportionally with

the distance from the food source, the amount of food that is received at a

given point is a circle that fades in intensity as it gets further from the source.

The line between those circles center points receives highest average amount

of nutrients (compared to the rest of the mold), and is the shortest distance

between the 2 food sources. Therefore, being attracted to the larger supply of

nutrients, the parts of the slime mold that are receiving less nutrients start to

travel to the places receiving more. In that way, the mold trims down the size

of the less efficient ways to the food sources.

Once the mold has utilized a sufficient amount of the resources in the

food source to regain lost mass during travel, it then repeats the process,

fanning out again towards where it detects traces of desirable substances,

such as glucose solutions, sucrose solutions, microorganisms, yeasts, and in

this case, oats covered in microorganisms.

In figure 3, the concept is shown; two red circles are put over the two

oats in the corresponding unmodified picture to the right. The amount of red inany one area represents the amount of food that is being received. The black

line shows the path between the circles that has approximately the most

amount of red, or food. It is visible how the most favorable path (in terms of

most nutrients) also happens to be the shortest path from one oat to the

other. It is in this way that we believe the slime molds choose their paths so

efficiently.

Several different factors could have affected the outcome of this

experiment. The two experimental environments where the experiments were

conducted were not completely identical, so any differences could have made

a change in the outcome; however, there are a few likely differences. Firstly,

light is known to be a deterrent to the organisms growth (Latty, Beekman).

Although light was present in both the control and the experimental


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environments, the light in the control groups habitat was more intense, and

could have caused the mold to grow in different ways than in the experimental

groups.

Another possible difference is that there were different levels of

humidity and temperature in the control groups and the experimental groups

habitats. The difference in humidity is evident in the experimental groups

pictures (see Figure 2). In some frames, excess water is visible, and near the

end of the experiment, a black-gray mold is seen to start growing in the Petri

dish. (Figure 1) This mold could have somehow had an adverse, or possibly

beneficial effect on the slime molds growth.

These possible differences could easily provide a stepping stone for new

experiments with slime mold. For instance, one could test how the mold reacts

to light by placing two oats in different places and providing light to only one

of those places. That way, if the mold could in fact detect light, and it did not

prefer light, it would grow more towards the oat which is not in the light.

Another experiment could include a temperature difference, with the control

mold being grown at room temperature, and two or four other groups of molds

being grown at different or extreme temperatures.

In conclusion, our hypothesis was confirmed by our data, and weshowed conclusively that slime mold in fact can react efficiently and quickly

when faced with a variety of environmental shapes. This one environmental

factor, combined with countless others, have been overcome by the slime

molds amazing ability to use chemical properties to solve its age-old problem

of possible starvation.


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Final Data:


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Figure 1: Black mold growth during the course of the experimental groups

run

Figure 2: Moisture buildup during the experimental groups run

Figure 3: Proposed nutrient distribution in P. Polycephalum


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Figure 4: P. Polycephalum fanning out in an attempt to search for food

Figure 5: LEGO mazes for experimental group Y


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Figure 6: LEGO maze for experimental group B

Graph 1: Distance from center oat

Graph 2: Distance from outer oats

0 1000 2000 3000 4000 5000 6000 7000 8000 90000

5

10

15

20

25

30

35

40

45

Distance from Center Oat

Group C

Group B

Group Y

Time since start of experiment (minutes)

Distance

(mm)


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0 2000 4000 6000 8000 10000

0

5

10

15

20

25

30

Distance from Outer Oats

Group C Average

Group Y Average

Group B Oat 1

Group B Oat 2


Distance(mm)

0 2000 4000 6000 8000 10000

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

Total Growth

Group C

Group Y

Group B


Percentofmaximump

ossiblegrowth


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Graph 3:Total growth

Works Cited

"Genomes | Physarum Polycephalum | The Genome Institute at Washington

University." Genomics Research | TGI | The Genome Institute at

Washington University. Washington University in St. Louis. Web. 09 May

2011.

.

Latty, Tanya, and Madeleine Beekman. "Food Quality Affects Search Strategy

in the Acellular Slime Mould, Physarum Polycephalum." Oxford Journals |

Life Sciences | Behavioral Ecology. 2011. Web. 09 May 2011.

.

Latty, Tanya, and Madeleine Beekman. "Food Quality and the Risk of Light

Exposure Affect Patch-choice Decisions in the Slime Mold Physarum

Polycephalum Read More:

Http://www.esajournals.org/doi/full/10.1890/09-0358.1."ESA Online


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Journals - Food Quality and the Risk of Light Exposure Affect Patch-

choice Decisions in the Slime Mold Physarum Polycephalum. Ecological

Society of America, 21 July 2009. Web. 9 May 2011.

.

Latty, Tanya, and Madeleine Beekman. "Speedaccuracy Trade-offs during

Foraging Decisions in the Acellular Slime Mould Physarum

Polycephalum." Proceedings of the Royal Society B: Biological Sciences.

18 Aug. 2010. Web. 09 May 2011.

.

Namleda, Kram. "Ode to Physarum." Educational Assistance. 19 Dec. 1999.

Web. 08 May 2011.

.

"The New Higher Level Classification of Eukaryotes with Emphasis on the

Taxonomy of Protists - ADL - 2005 - Journal of Eukaryotic Microbiology."

Wiley Online Library. Oct.-Nov. 2005. Web. 10 Feb. 2011..

"Physarum Polycephalum and Other Acellular Slime Molds." Educational

Assistance. 16 Aug. 2005. Web. 09 May 2011.

.

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