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Extreme Evolution

My research focuses on two species which are examples of extreme evolution. One is the yeast Nadsonia fulvescens, and the other is the mushroom Morchella esculenta.

yeast and mushroom

The yeast is found nowhere but St. Petersburg, Russia, because that is where the most extreme evolution of fungi is occurring. Apparently, consistently cool and humid air from the Baltic Sea keeps the environment ideal for fungi evolution. Mushrooms in Northwest Russia are more diverse than anyplace else on the planet.

Yeasts evolved from filamentous fungi after modern biology began when the dinosaurs died out. What is not being clarified about the dinosaurs dying out is that all biology transformed drastically into its modern forms. During dinosaur years, biology was highly restricted by nonwoody brush which covered the lowlands. Mountains were small and not yet developed like now days.

Prior to dinosaur years, tectonic plates were thin, because cool-down of the planet is a slow process causing tectonic plates to get thicker. Even a lot of scientists don't seem to realize the consequences. The thin plates would stick together as they collided creating super continents. At the time dinosaurs formed, around 252 million years ago, all landmasses were stuck together to form Pangaea. Mountains were just starting to get significantly large. Before then, mountains were not large, because tectonic plates were thin.

The formation of significant mountains during dinosaur years allowed some diverse evolution to occur on the hills. Conifer trees evolved on the hills, and diverse species evolved around the conifers. Flowering plants evolved, but they were so rare that they weren't located in fossil evidence until a few years ago. Flowering plants were not shaping the ecology as they do now days.

When dinosaurs died out 66 million years ago, grass destroyed most of the oppressive brush which was holding back evolution. Modern biology is now shaped by flowering plants, broadleaf trees and grass. The flowering plants allowed yeast to evolve in the resulting sugary solutions. Yeasts fought off bacteria by excreting acetic acid and ethyl alcohol. Yeasts also caused fat production to evolve, because acetic acid production is very similar. Fat is approximately a bunch of acetic acid molecules linked together. Fat production was then transferred to other species including animals through horizontal gene transfer.

The central property of filamentous fungi is their ability to resist dehydration. This property allows them to grow on surfaces, where drying occurs between rains. Surface growth caused the filamentous shape, which is a rudimentary type of motion on surfaces.

The ability to tolerate dehydration is an extremely demanding property which yeast gave up in growing in sugary solutions. Yeasts cannot grow on exposed surfaces, because dehydration would destroy them. Yeast spores, however, can tolerate a degree of exposure and dehydration.

Yeast spores normally form inside the cells. There is one exception: Nadsonia fulvescens (and a related species) forms spores outside the cell. My research explains why.

Most yeasts love to grow on tree exudate, but they can't adapt to it, because the exudate is too transient. Trees can stop producing exudate, and rain can wash the exudate away, which leaves the yeast exposed to a harsh environment causing dehydration. Nadsonia fulvescens adapted to growing on tree exudate by forming a spore immediately when the exudate is no longer available.

The Nadsonia spore must be outside the cell for the same reason that mushrooms form. The process is called endotrophism. It means nutrition from within. When nutrients are no longer available, internal reserves must be used to form the spore.

Yeasts have hard cell walls which do not shrink in size. When internal nutrients get used up, the total volume reduces, and the cell mass must move into a new structure which is smaller. The need for a smaller structure required the spore to form outside the cell.

Soil mushrooms do something similar. They store up nutrients in the mycelium for several weeks. When conditions get right, the mushroom forms from the stored up mass. This allows the mushroom to form rapidly, so it can get spores out before being damaged by dehydration or insects.

Evolving this physiology in a yeast is so demanding that it only occurred in St. Petersburg Russia, and the yeast cannot survive anyplace else because of its narrowly defined requirements. Presumably, conditions are too hot and dry too often everywhere else. A related species in the same genus, Nadsonia elongata, is found in many costal areas, because it evolved the ability to grow under loose tree bark which provides greater protection.

The mushroom which I studied, the morel, has extremely unusual characteristics. It does not have a cap with gills producing spores. Instead, it forms spores within the tissue, like yeasts do. This method of producing spores is extremely problematic preventing spores from being disseminated easily. As a result, morels acquire highly localized characteristics with recognizable genetic differences every few hundred miles of ground space.

Morels follow sandy river basins and will not grow on clay type soils. The reason is because the mycelium will not tolerate dehydration. Sand does not dehydrate due to its lack of capillary action. Clay has strong capillary action due to its fine texture. This property cause moisture to move to the surface and evaporate away resulting in rapid drying of clay type soils between rains, unless a lot of organic matter or cultivation breaks up the motion of water upward.

The extreme limitations caused by spores inside of cells was not an evolved property of morel mushrooms, as there is no advantage. Instead, the property is a disadvantageous carry-over from its ancestor—a yeast. The morel has yeast-like properties in all of its characteristics except morphology (shape).

The morel shows that morphology can evolve easily, while physiology is difficult to change. Morphology can change simply by counting a different number of cells in any direction, but physiology cannot change so easily, because enzymes must be fixed in an exact location much like an assembly line. Moving anything around is highly disruptive.

The morel re-evolves during each ice age cycle, as indicated by spore surfaces for two cup fungi which also form spores inside the cells. Ice ages have been cycling at 100 thousand years, which is an extremely short amount of time for such drastic changes. It means the morel evolved from a yeast less than 100 thousand years ago. Most of that evolving would have occurred at the base of trees, where yeast filaments would have reached down into the soil and fed upon bacteria by excreting acid.

There seems to be something about ice ages that causes a yeast to evolve soil growth. It is probably the front of ice sheets that creates ideal conditions where dehydration of the yeast does not occur.

Innumerable properties of the morel mushroom show how dramatic evolution occurs in the transition of a single-celled organism into a multi-celled organism in a few short years. The morel still maintains numerous disadvantageous properties. An example is autolysis, which means self-breakdown. All bacteria and yeast break down as they die off for the purpose of recycling nutrients. Large molecules are broken down enzymatically into subunits which provide ideal nutrients, not only for the same species but for plants also. Residual autolysis in the morel results in tissue break-down as morels age. Bacteria grow on the deteriorating tissue, which can cause sickness when eating old morels.

To survive through an ice age cycle, the morel must evolve into a cup fungus. Cup fungi are better adapted to getting spores out of the tissue, because there is a gradient of drying rates from rim to bottom of the cup. Drying rate is important, because it must be delayed enough to allow spores to form and then dry enough to shrink the tissue and create a propelling force for the spores.

The morel will never evolve into a cup fungus fast enough to survive beyond the present ice age. But there is a related species, Helvela crispa, which already has a good start and will probably evolve into a cup fungus. The morel sometimes has an indent on the side, which starts the evolution into the cup shape and shows the need for that morphology. But the morel shape prevails where there are rich nutrients, because there is much more surface area with that shape. Helvela grows later in the year when nutrients are more scarce causing it to adapt to extreme conditions.

Yeast evolution was quite dramatic, as filamentous fungi adapted to sugary solutions. Such drastic change in morphology and physiology preconditioned a yeast for the dramatic evolution from a single-celled organism into a multicellular mushroom.

 

         
 
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