Biodiversity – Oct. 3/12
- Fungi eukaryote phylogeny: We are focusing on the Unikots clade, the main groups of which are fungi
and animals. Opisthokonta is a monophyletic group and is a branch of the unikots. The monophylya
of opisthokonta is strongly supported by molecular, morphological, and other data. The first keys
papers on this were in 1993 – Baldauf and Palmer, Wainwright et al. Amoebozoa (amoebae, slime
molds) are another group of unikots, but we will not be discussing them. Fungi and animals are more
closely related to one another than either are to plants. The work of Woese et al. put an end to the use
of the old 5 kingdom classification.
- Evolution of fungi: There is very little fossil evidence of fungi. Fungi evolved from an aquatic
unicellular eukaryote. During the Ordovician period (450MYA) fungi had a major role in the
colonization of land. There is fossil evidence of terrestrial mycorrhizal fungi from the Devonian
- What is a fungus?: A fungus is eukaryotic and its cell walls contain chitin (this is a synapomorphy).
Fungi are heterotrophic and they have extra-cellular digestion and absorptive nutrition. They are not
photosynthetic. They don’t have chloroplasts and they do not require light. They can grow anywhere
(but very few are marine) and in the dark. Fungi can be predators, parasites, mutualists, saprobes,
and disease-causing. They can be freshwater aquatic (very few are marine), terrestrial, soil, and they
can be located in and on living and dead tissue. Few are unicellular (yeasts) and most are
multicellular and filamentous. Most reproduce sexually and some reproduce asexually. Most are
aerobic and few are obligate anaerobes.
- Most fungi are multicellular and filamentous: The vegetative stage (non-reproductive stage) consists
of cylindrical thread-like filaments. The reproductive stage varies in morphology, depending on
taxon. Hypha (plural hyphae) is the same thing as the filament. Hyphae are unicellular or
multicellular, they contain one to several nuclei per cell, and they are microscopic. Hyphae form 3D
branched structures called mycelium (plural mycelia) in or on a substrate. Hyphae aggregate
together and form bundles. Mycelia are non-reproductive parts.
- Extracellular digestion and absorption: Fungi, like plants, produce secondary metabolites, which are
metabolites that are not involved in growth and reproduction. The secondary metabolites that fungi
produce are antibiotics. They are defensive chemicals that kill bacteria. In fungi, a spore germinates
and a hypha grows off of it. The fungus excretes an exoenzyme to outside the cell (extracellular). The
substrate or starch is the food and the enzyme breaks down the starch into smaller and smaller parts,
to the point where the fungi can absorb the nutrients from the starch. The enzymes are creating a
food source. Other organisms, for example bacteria, are attracted to the food and come near the
fungus and try to take the food. The fungus has evolved secondary metabolites (antibiotics) that it
releases to outside of the cell to kill the bacteria.
- Fungi today: Mycology is the study of fungi. There are 5 monophyletic phyla (and some other smaller
unplaced groups). Hibbett et al. 2007 did phylogeny and classification. There are 100,000 described
species of fungi worldwide, and it is estimated that there are 1.5 million total species, mostly in the
tropics. There are 300,000 described plant species, but there probably aren’t too many undescribed
ones out there still.
- Five phyla of fungi – these are based in part on the morphology of their sexual reproductive
structures: Phylum Basidiomycota (most well-known to us), Phylum Ascomycota, Phylum
Zygomycota, Phylum Chytridiomycota (1000 described species worldwide, freshwater aquatic,
microscopic, motile with flagella), Phylum Glomeromycota (150 described species worldwide, all
form mycorrhizal relations with plants, asexual spore production in soil). - Phylum Basidiomycota: There are 40,000 described species worldwide. They are commonly called
mushrooms or mushroom fungi. They are the only organisms that can significantly degrade lignin.
Lignin is a structural compound (wood) found in plant cells. Many of these organisms are
decomposers and some are mycorrhizal. Some are jelly fungi and yeasts. They are morphologically
diverse. Plant-disease causing: rusts and smuts. Mushrooms are a major food source for animals.
Some are edible, but many are toxic to humans. In jelly fungi, the outer surface, top, and bottom are
- Mushrooms: Mushrooms are the macroscopic sexual reproductive structure of most Basidiomycota
(and some Ascomycota). Their function is to produce, liberate, and disperse sexual spores (haploid
spores). Often we don’t see the hyphae or mycelium of the fungus. It is too small or hidden in the
substrate (soil/ground). The parts of the fungus we see are usually the reproductive structures, such
as mushrooms, which are connected to the myce