Directional Awareness in Basidiomycetes

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Contents

Abstract

Basidiomycetes have specific mechanisms to release their spores. This spore mechanism is associated with the growth direction of the fruiting body. The fruiting body of this group always orient upward with cap over stem. Thus, we hypothesized that the fungi must have the direction awareness when we change the orientation of the substrate. In examining this hypothesis, we set 40 fungi's fruiting bodies in Maliau Basin to be changed 90o in their position. Our results showed that there were no significance result in the association between the change in angle and stem type or morphotypes. However, nearly significant result was observed in one morphotype (Mor10). Additionally in morphotype 4, 80% of fruiting body caps changed direction. These results were probably a product of having too many morphotypes and too few individuals in each morphotype. Still, the patterns we did see were intriguing and further study will show these patterns hold true in many fruiting body types.

Introduction

Instead of its distinct DNA and morphological characteristics, fungi had been considered as a subject in plant science for a long period of time. This situation led to the misguided expectation that the physiology of growth in plants should be the same with the physiology of growth in fungi. Thus, the study of the growth mechanism in Fungi—including their response to light and gravity-- should be more developed (Moore 1996). Kaneko and Sagara (2001) found that the fruiting body of Agaricales mushrooms showed positive phototropism and negative gravitropism in the later stage. Moore (1996) stated that gravity response is important for the fungi growth due to its association with spore liberation.

In this project, we specified our study in the growth mechanism of the Basidiomycetes. Pertaining to its spore release mechanism, Basidiomycetes have a little droplet of water which falls on to the spore and pushes it down. This mechanism happens in the structure called pores or gills located below the cap of the fruiting body. Thus, the spores will fall out of the cap and into the wind. In addition, this position also protect the spores in the gills from the pouring rain (Moore 1996).Therefore it is necessary that the fruiting body is in the correct direction so that the spore will fall down into the wind.

Maliau Basin has a huge biodiversity of Basidiomycets fungi. As we observed, all of them always orient their fruiting bodies upward with cap over stem. Based on the information explained above, we intended to do project in examining whether fungi has directional awareness if we change the direction of the substrate in which they live. We expect that the finding of this project will give more information about the growth mechanism in fungi.

Question

Will the orientation of the substrate affect the direction of growth in a Basidiomycete's fruiting body?

Methods

To begin our experiment we selected a short loop of path in Maliau Basin that was easily accessible and where many types of fungi has been observed previously. We set up the experiment in the morning around 9am. We walked along the path scanning the forest floor for 20 visible fungi fruiting bodies. When one was observed we isolated it on the substrate and rotated the substrate so the fruiting body was approximately 90º changed from it's original position. After rotating the fruiting body we measured the angle at which the fruiting body was positioned by selecting a reference point for the “0” mark on a protractor. We also took multiple photographs of the fruiting bodies in order to compare the appearance of the fruiting body later in the day. We also took note of the stem type of the fruiting body. After approximately 8 hours (around 5pm) we went back to the rotated fruiting bodies and remeasured the angle of their position. We again took pictures of all the fruiting bodies in order to see the change in the cap of the mushrooms. Two days later we replicated the entire experiment with 20 new fruiting bodies. We did not specifically focus on one morphotype. Instead we purposefully selected the widest range of morphotypes as well as fungi both on leafs and on sticks. We chose this method of sampling because we believed there would be a wide range of responses in different types of fruiting bodies. By maximizing the variety of morphotypes we maximized the chances of observing an interesting pattern.

Analysis

After collecting the data we calculated the angle change from the original observation (angle 1) to the second observation (angle 2). After reviewing the photographs we determined if the fruiting body cap had changed position (ccap). We then categorized the fruiting bodies into morphotypes and stem types. Using the statistical package R we then analyzed our results to determine if there was an association between the characteristics we measured. First, we ran two linear models to examine how the angle change is influenced by the stem type and morphotype. We then ran two chi squared analysis to compare change in cap with stem type and morphotype. Finally we looked at each morphotype individually to observe any obvious patterns in the change in angle, change in cap, or stem type.

Results

Within the 40 fruiting bodies measured, we observed 14 morphotypes and four stem types: short and thin (ST), short and fleshy (SF), long and thin (SF), or long and fleshy(LF). We found no significance in the linear model comparing change in angle with stem type (P-value for all stem types >> 0.05). We also found no significance using the chi-square tests to analyze association between change in cap and stem type (P-value = 0.428) and between change in cap and morphotype (P-value = 0.517). When running the linear model to analyze the association between change in angle and morphotypes however, we nearly found significance with one morphotype (P-value for Morph 10 = 0.06). When analyzing each morphotype individually, we found that 80% of fruiting bodies in morphotype 4 showed a change in cap. No other morphotypes showed any relevant patterns.

The linear model analysis comparing the change in angle with morphptypes

Disscussion

While at first the lack in significance of our tests was surprising, we believe several factors contributed to these results. First, by grouping all our data together to analyze change in angle and stem type and cap change and stem type, the possibility that different morphotypes of fruiting bodies would inherently have different characteristics could not be taken into account. When we did sort the fruiting bodies into morphotypes to take this possibility into consideration, we found that our attempt to maximize diversity meant we had too many morphotypes with too few individuals in each. This made it unlikely to find significance. For example in the analysis Morphotype 7 did not show a statistically significant change in angle or cap, however one fruiting body in that morphotype showed the most dramatic change in angle and cap of all the fruiting bodies sample. If this study were to be repeated, we would be sure to have many more individuals for each morphotype. Despite these problems, the patterns that we did find with our data were very interesting. When reviewing the photographs, one fruiting body in Morphotype 10 visibly showed one of the largest changes in both angle and cap. It was also quite visible that almost all the fruiting bodies in Morphotype 4 showed a change in cap. These changes that were so easy to observe were much harder to quantify as seen in the non-significance of our results, however if the experiment were to be repeated we believe the patterns we observed would hold true across these two morphotypes.

References

Kaneko A and Sagara N. 2001. Responses of agaric fruit-bodies to light and gravity: grwoth straight downward in response to light from below. Mycoscience 42: 67-74.

Moore D. 1996. Graviresponse in Fungi. Adv.Space Res. Vol 17, NO 6/7,pp (6/7)73-(6/7)82.