Evolution, ecology and mycophagy in the hypogenous fungi

Abstract

The mycorrhizal hypogeous fungi are linked t o epigeous species through
a series of increasingl y reduced forms. For example, Bol etus is repr esented
in secotioid groups in the genus Gastroboletus , which in turn is r epr esented
in the hypogeous group in the genus Truncocolumella. Truncocolumella seems
has evolved to a reduction of the stipe , that characterizes GastroboletUS;
Truncocolumella has only a columella.
Even further r eduction of the hypogeous habit is shown in the genus
Rhizc;'pogon. Though similar to Truncocolumella in mos t ways, it lacks a columella.
This morphologic reduction of the hypogeous fungi relates to adaptations f o r
spore dispersal by animals, ranging from small gnats to elk and bear. The
hypogeous fungi have evolved e l aborate chemical mechanisms to attract animals.
When the sporocarp mat ur es, ar omatic substances are produced with increasing
intensi ty until the sporocarp is detected by an animal , which then , excavates
and eats it . The sporocarps are high in minerals, amino acids and vitamins; they
may serve as a major source of minerals for animals in areas where salt l icks
are scarce. The animal digests all the spor ocarp tissues , but the spores pass
through t he digestive tract unharmed. Animals feces are "packages" of spores
with a high inoculum potential. Once deposited, the spores are washed into the
soil to contact potentially receptive r oots of their mycorrhizal hosts. Some
animals also have special adaptat i ons for use of hypogeous fungi in their diet,
and , in some cases, have co- evolved a dependa nce on them for survival.