Chapter 22
The evolution and Diversity of
Fungi
• Domain Eukarya, Kingdom Fungi
• Most are multicellular (except for yeasts)
• Nonmotile (cannot move towards food or mates, have to
grow to them)
•
Used to be classified with plants, but new molecular
analysis indicates that fungi and animals likely came
from a common ancestor (aquatic flagellated organisms,
that eventually lost their flagella as they adapted to life
on land; plus fungi have no chloroplasts and no cell
membrane)
• Opisthokont= of the clade Opisthokonta, all organisms
that descended from a common ancestor with a
posterior (opistho) flagellum, including animals, fungi,
and some protists
Evolution of Fungi
• Has been suggested fungi evolved from
red algae because both fungi and red
algae lack flagella in all stages of the life
cycle.
22.1 Fungi Live by absorptive
heterotrophy
• Nutrition—all are heterotrophs and
acquire nutrients by absorptive
heterotrophy.
– Cells release digestive enzymes
(exoenzymes) and then absorb resultant
nutrient molecules.
Unicellular Yeasts absorb nutrients
directly
• Unicellular free-living fungi are referred to
as Yeasts
• They also absorb nutrients directly through
their cell surfaces
• Many reproduce by budding
Multicellular Fungi use hyphae to
absorb nutrients
• Basic body plan is a network of filaments called a mycelium.
• One filament is called a hypha. (hyphae plural)
– Absorption of nutrients takes place here
• Cell walls are composed of chitin—a nitrogen containing
polysaccharide
• Some fungi are septate—cells that have incomplete cross
walls (have septa-cells with incomplete cell walls)
• NonSeptate fungi are also coenocytic—hyphae lack septa,
but may contain hundreds of nuclei.
• Energy reserve is glycogen, not starch.
Cell wall made of chitin, which
is also found in the shells of
insects and some other
arthropods
Haustoria-branching projections that push through
cell walls into living plant cells, absorbing the
nutrients within those cell. Found in parasitic fungi
Mycelium of Fungi
Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)
• Some produce sexual spores where
portions of the mycelium create fruiting
structures (mushroom)
• Rhizoids are modified hyphae that anchor
them
http://www.atsu.edu/faculty/chamberlain/Website/Lects/fungi9.jpg
Fungi are in intimate contact
with their environment
• Habitats—Must live where there is an organic
source of food.
• Many live where it is damp and shady.
• Parasites live in or on another organism.
• Large surface area-to-volume ratio which is
good for food but bad for water loss
http://www.homestead.org/DustinEirdosh/Fungus/Mycorrhizae.jpg
22.2 Fungi Can Be Saprobic,
Parasitic, Predatory, or Mutualistic
http://www.bio.miami.edu/dana/pix/morel.jpg
Saprobic fungi are critical to the
planetary carbon cycle
http://www.kolumbus.fi/ilona.barlund/ilona.barlund/Lig_BioSpek4_engl_Net.jpg
Figure 31.0x Decomposers
Some fungi engage in parasitic or
predatory interactions
http://www.todayshomeowner.com/wp-content/uploads/2011/10/how-use-predator-insects-control-garden-pests-5.jpg
Parasitic Fungi
• Facultative parasites grow on living
organisms but sometimes by themselves
• Obligate parasites grow only on specific
living host (plant or insect)
• The hyphae invade the host and some
develop a haustoria-branching projections
that push through cell walls into living plant
cells and absorb nutrients
Smuts and Rusts
Figure 31.20x2 Pink ear rot of corn
Pathogenic Fungi
• There are many fungi that can harm humans
• Most people with aids die from a fungal
disease…ex: Pneumocystis jirovecii
(pneumonia) & Candida albicans (incurable
diarrhea)
• Can also cause athletes foot and ringworm with
many others
• Also destroy multiple cash crops
Figure 31.20 Examples of fungal diseases of plants: Black stem rust on wheat (left),
ergots on rye (right)
Cordyceps
http://1.bp.blogspot.com/-dT9B5bpDSSU/UarrxJO4KvI/AAAAAAAADJQ/wRkp0B5niP8/s1600/q.jpg
Predatory Fungi
• Some fungi can trap nearby microscopic
protists or animals
• Some secrete a sticky substance and
attach to their host and then invade them
• Other soil fungi create a ring and trap
nematodes and invade them with hyphae
instantly (just like fishing)
http://www.uoguelph.ca/~gbarron/N-D%20Fungi/n-dfun1.jpg
Mutualistic fungi engage in
relationships beneficial to both partners
• Symbiotic-the partners live in close,
permanent contact with each other
• Mutualistic-the relationship benefits both
partners
Symbiotic Relationships
• Lichens
– Association between a fungus and a
cyanobacterium or green alga.
• Specialized fungal hyphae penetrate photosynthetic
cells and transfer nutrients directly to the fungus.
• Can live in areas of extreme conditions and
contribute to soil formation.
Lichen Morphology
Figure 31.17 Anatomy of a lichen
Figure 31.17x Anatomy of a lichen
Figure 31.16 Lichens
Symbiotic Relationships
• Mycorrhizae—mutualistic relationships between
soil fungi and the roots of most plants
– Plants with mycorrhizas grow more successfully in
poor soils than those without them
– increases absorptive area of plant roots and plant
roots food source
– Truffles are mycorrhizal fungi living in association with
oak and beech tree roots (are very costly-$800./pound?)
Figure 31.18 Mycorrhizae
Figure 31.19 An experimental test of the benefits of mycorrhizae
Endophytic fungi protect some plants
from pathogens, herbivores, and stress
• Fungi that live within aboveground parts of
plants without causing obvious deleterious
symptoms are called endophytic fungi
• Some of these help the host with the fungi
growing on it by defending the host
http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Ergot01.jpg/200px-Ergot01.jpg
22.3 Major Groups of Fungi Differ
in Their Life Cycles
http://www.ont-woodlot-assoc.org/photos/mushroom%20web%20use/mushroom-life-cycle.gif
Fungi reproduce both sexually and
asexually
• Asexual reproduction:
– 1.production of haploid spores within sporangia
– 2. production of haploid spores not in sporangia at the
tip of hyphae called conidia
– 3. Cell division by unicellular fungi (fission or budding)
– 4. simple breakage of the mycelium
• Sexual reproduction-hyphae from two different
mating types fuse.
– Hyphae that contain paired haploid nuclei are said to
be dikaryotic.
– Fungal spores germinate directly into haploid hyphae
without embryological development.
Figure 31.15 Budding yeast
Microsporidia are highly reduced,
parasitic fungi
• Microsporidia are unicellular parasitic
fungi
http://web.stanford.edu/group/parasites/ParaSites2006/Microsporidiosis/microsporidia1_files/image004.jpg
Most chytrids have an aquatic life
cycle
• Chytrids include several distinct lineages
of aquatic microorganisms once classified
with the protists
Chytridiomycota (myc
= fungi):
flagellated, likely the
most primitive fungi
Some fungal life cycles feature separate
fusing of cytoplasms and nuclei
• Most of the remaining groups are mainly
terrestrial
• No motile gametes and do not release
them into the environment
• Cytoplasms of two individuals of different
mating types fuse-plasmogamy then the
nuclei fuse in a process called karyogamy
Figure 31.3 Generalized life cycle of fungi (Layer 3)
Zygospore fungi
• Called the zygospore fungi from the thickwalled zygospore that develops after the nuclei
of two mating types pair and then fuse
• Mainly saprotrophs living off plant and animal
remains in the soil or food in the kitchen
• Some are parasites of small soil protists or
worms, and even insects such as houseflies
• Example is black bread mold, Rhizopus
stolonifer
Figure 31.6 The common mold Rhizopus decomposing strawberries
Zygomycota
release of
pheromones
Rhizopus, common
mold, also called
black bread mold
• Hyphae produce gametangia which come
together and form a zygosporangium
• The zygosporangium have many haploid nuclei
• The haploid nuclei then form diploid nuclie within
a unicellular zygospore
• Remains dormant until conditions are good and
then a stalked sporangiophore sprouts which
contain sporangia
• This is where meiosis happens and spores are
produced for germination later
• Zygosporangia are
resistant to freezing
and drying– enter a
stage of metabolic
inactivity– then
when conditions
improve, they
release lots of
spores!
This is Pilobus, it decomposes animal dung,
and can aim its spores toward the sun, and
subsequently, grassy areas, as far as 2m
away!
Figure 31.7 The life cycle of the zygomycete Rhizopus (black bread mold)
Figure 31.7x1 Young zygosporangium
Figure 31.7x2 Mature zygosporangium
Arbuscular mycorrhizal fungi form
symbioses with plants
• Arbuscular mycorrhizal fungi-terrestrial
fungi that associate with plant roots in a
symbiotic, mutualistic relationship
http://archive.bio.ed.ac.uk/jdeacon/FungalBiology/fig13_1b.jpg
The dikaryotic condition is a synapomorphy
of sac fungi and club fungi
• Dikaryon-stage of the fungal lifecycle
where two genetically different haploid
nuclei coexist and divide within each cell
of the mycelium (n+n)
http://bcs.whfreeman.com/thelifewire8e/content/cat_010/f30013c.jpg
The sexual reproductive structure
of sac fungi is the ascus
• Most sac fungi are saprotrophs that digest
resistant materials containing cellulose,
lignin, or collagen.
– Most are composed of septate hyphae.
– Ascus (asci singular) refers to the fingerlike sac
that develops during sexual reproduction.
• Asci usually surrounded and protected by sterile
hyphae within an asocarp.
– Asexual reproduction involves production of
conidiospores.
Ascomycota (“sac” fungi)
• Many are decomposers, e.g. cup fungi,
morels, and truffels
• Some are parasitic on plants, e.g. powdery
mildews, chestnut blight, and Dutch elm
disease
• Yeasts are unicellular ascomycotes that
are unicellular and reproduce asexually by
budding
Figure 31.20x1 Strawberries with Botrytis mold, a plant parasitic fungus
The sexual reproductive structure
of club fungi is the basidium
• Called the club fungi from basidia (single
basidium) (basiditomata-book), club-shaped
structures that produce sexual basidiospores
• Have septate hyphae
• Include decomposers such as mushrooms,
backet fungi, and puffballs
• Also include parasites such as smuts and rusts
basidiospore
gills
basidium
Figure 31.12 The life cycle of a mushroom-forming basidiomycete
Figure 31.11 Basidiomycetes (club fungi): Greville's bolete (top left), turkey tail
(bottom left), stinkhorn (right)
Figure 31.11x1 Coprinus comatus, Shaggy Mane
Figure 31.11x5 Amanita
Figure 31.11x2 Geastrum triplex
22.4 Fungi Can Be Sensitive Indicators
of Environmental Change
http://upload.wikimedia.org/wikipedia/commons/d/da/Lichen_reproduction1.jpg
Lichen diversity and abundance
indicate air quality
http://4.bp.blogspot.com/-DW0S8_ZleYg/T7Sr0umeKxI/AAAAAAAAAgo/Q50SKEM_LtE/s1600/lichen.jpg
Fungi contain historical records of
pollutants
http://andberlin.com/wp-content/uploads/2012/09/fungi-at-botanical-museum.jpg
Reforestation may depend on
mycorrhizal fungi
http://www.americanforests.org/wp-content/uploads/2014/10/3.-Diagram-of-seedling-and-ectomycorrhizal-fungi-CCripps_web.jpg
Figure 31.13 A fairy ring