Fungal duo teaches evolutionary lesson.

Fungal duo teaches evolutionary lesson

Biologists usually classify orgnaisms by their appearance, but new research suggests this may lead to misclassifications. "Looking at molecules [as opposed to appearance] may give us better assignments for [organisms'] place within the phylogenetic tree of life," says Jeffrey D. Palmer of the University of Michigan in Ann Arbor. "And the correct phylogenetic assignment is really just the starting point to understand the evolution of that organism."

By examining DNA, Palmer and his colleagues discovered a close genetic similarity between the umbrella-shaped Suillus mushroom and a ball-like, soil-living "false truffle" -- one of the first and perhaps most extreme cases in which scientists have found an organism to have evolved directly from another, very different-looking organism, Palmer says.

In the past, biologists were unable to confirm any relationship between the false truffle Rhizopogon subcaerulescens and other fungal species. They thought R. subcaerulescens was derived, although separate, from members of the family Boletaceae, which includes Suillus, but they viewed the relationship as a distant one, says coauthor Thomas D. Bruns at the University of California, Berkeley.

Bruns, Palmer and their co-workers found that the false truffle's mitochondrial DNA is structurally identical to that of 14 Suillus species, suggesting the two fungal types should be placed in the same subfamily, Bruns says. They theorize that the false truffle rapidly evolved its drastically different shape through changes in a small set of genes important in fungal development. These changes probably were prompted by strong selection pressure to reduce water loss and to disperse spores via animals, the researchers write in the May 11 NATURE.