The morel mushroom evolved from a single-celled yeast into a multi-celled mushroom over the past 70 thousand years. This appears to be one of the few examples of a single-celled organism evolving into a multi-celled organism in the past 100 million years, beyond some molds which could be doing something similar on a smaller scale.
Rapid change is still occurring with the morel. It must evolve into a cup fungus to survive through the next ice age. It won't get there, but a related species, Helvela crispa (H.c.) probably will. H.c. is like a potato chip on a stalk. The stalk can shrink and touch the ground, while the potato chip curves upward into a cup shape.
There are two closely related cup fungi which evolved as the morel did during previous ice age cycles. They have the same surface pattern on their spores as the morel, which means they evolved from the same yeast, which is probably Schizosaccharomyces japonicus.
There have probably been dozens of cup fungi evolved in the past, but they die out, because the cup shape is a failing attempt to cope with ascospores, which result from evolving from a yeast.
Ascospores form within cells. They do not disperse easily. To get them out, the tissue must dry and shrink to create a propelling force. But if the tissue dries too soon, the spores fail to form. So there must be rainy conditions for three days, and then dry conditions to propel the spores out.
The cup shape copes with the problem by creating slow-drying tissue near the ground and fast drying tissue extending into the air. Someplace in between, the tissue is supposed to dry at just the right rate to get spores out. It seems to work for a couple of ice age cycles before die-off of the species occurs. Ice ages have been cycling at precisely 100 thousand-year intervals for the past ten cycles.
The age of the morel can be pinned down to 20 thousand years as a free-growing mushroom based on the length of an ice age. About 30 thousand years would be required to form an ice sheet. About 50 thousand years would be required for a yeast growing at the base of trees to evolve multi-cellular characteristics. And the remaining 20 thousand years allowed the mushroom to evolve crude morphology and variant strains.
Something about the front edge of a glacial ice sheet allows a yeast to evolve into the morel mushroom. It is also where human agriculture began at the same time. As the ice sheet forms, it draws moisture out of the air due to the cold temperatures above it. The resulting dry air creates desert-like conditions in front of the ice sheet. Between the ice and the desert would be every imaginable ecosystem in a small amount of space.
Continue reading at: http://english.pravda.ru/science/earth/15-07-2013/125132-morel_mush...