Evolutionary Ecology
 | Mycorrhizal symbiosis and coevolution | |
Evolutionary links between vegetative dormancy and mycorrhizal association
Orchids begin life as dust seeds that germinate in the wild only after contact with
an appropriate fungal host. The fungal connection that develops, a kind of internal
mycorrhiza similar in morphology to the arbuscular mycorrhiza (AM), provides the
orchid with not only nitrogen, phosphorus, and other nutrients, but at times also
carbon, which the orchid generally does not make during its first several years of
life. Some orchid species have evolved to rely on this connection for their whole
lives, including the North American ghost orchid species Cephalanthera austiniae.
Do photosynthetic species continue to utilize fungal carbon into adulthood? If so,
then the orchid family has evolved a tendency for parasitism not found in the rest
of the plant kingdom, as orchids also often parasitize their pollinators through
deceptive pollination (i.e., luring pollinators with a nectar-like scent, rather than
actually producing real nectar, which is expensive).
Orchids begin life as dust seeds that germinate in the wild only after contact with
an appropriate fungal host. The fungal connection that develops, a kind of internal
mycorrhiza similar in morphology to the arbuscular mycorrhiza (AM), provides the
orchid with not only nitrogen, phosphorus, and other nutrients, but at times also
carbon, which the orchid generally does not make during its first several years of
life. Some orchid species have evolved to rely on this connection for their whole
lives, including the North American ghost orchid species Cephalanthera austiniae.
Do photosynthetic species continue to utilize fungal carbon into adulthood? If so,
then the orchid family has evolved a tendency for parasitism not found in the rest
of the plant kingdom, as orchids also often parasitize their pollinators through
deceptive pollination (i.e., luring pollinators with a nectar-like scent, rather than
actually producing real nectar, which is expensive).
Caption: Cross-section of the root cortex of a Cypripedium guttatum individual. Fungal
hyphae form intracellular mycorrhizal connections in the cortical cells of the plant
root. It is thought that this is where fungal nutrients are absorbed by the orchid. Photo
taken by Ian Herriot, and appears in Shefferson et al. 2005 (Molecular Ecology).
hyphae form intracellular mycorrhizal connections in the cortical cells of the plant
root. It is thought that this is where fungal nutrients are absorbed by the orchid. Photo
taken by Ian Herriot, and appears in Shefferson et al. 2005 (Molecular Ecology).
Our research on the orchid mycorrhiza first focused on identifying the dominant
mycorrhizal fungal hosts in genus Cypripedium. This project involved sampling
six species from across North America, and one from Europe, and using DNA
methods to identify the fungi to family. Results indicate that Cypripedium species
associate with generally unnamed members of the fungal family Tulasnellaceae,
which a rather obscure group of fungi in Division Basidiomycota.
mycorrhizal fungal hosts in genus Cypripedium. This project involved sampling
six species from across North America, and one from Europe, and using DNA
methods to identify the fungi to family. Results indicate that Cypripedium species
associate with generally unnamed members of the fungal family Tulasnellaceae,
which a rather obscure group of fungi in Division Basidiomycota.
Copyright 2010 Richard P. Shefferson. All rights reserved.
Research Interests
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Parasites are often highly specialized to their hosts. The result is that specificity is
often so high that host and parasite speciate in parallel. In Cypripedium, although
specificity appears high, it is not high enough to suggest simple
one-species-to-one-species relationships, as might be evident in some parasites
of mammals (e.g., lice).
We explored the evolutionary context of mycorrhizal specificity in Cypripedium,
expanding my previous study to include 14 species (15 taxa) across North
America, Europe, and East Asia. We estimated specificity as a quantitative
character, using the mean phylogenetic distance among mycorrhizal fungi per
species as the appropriate metric, and mapped this measure onto a phylogeny of
the genus Cypripedium. The results suggest that specificity is an evolving trait,
and that evolutionary history is an important determinant of its value, because
closely related Cypripedium species share more similar values of specificity than
do distantly related Cypripedium species.