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Nutritional roles
• Saprotrophy
– nutritional utilization of non‐living material
HMB436H – Medical & Veterinary Mycology
Lecture 3 – Fungal ecology
• Biotrophy
– nutritional utilization of living material
t iti
l tili ti
f li i
t i l
• facultative
• obligate
Dr. James Scott
Dalla Lana School of Public Health
University of Toronto
What's
for lunch?
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Saprotrophs
White rot
• bioconvert dead material (classical "decomposers")
• many fungi have the ability to grow saprotrophically
• saprotrophs are often closely associated with other organisms (symbiosis)
organisms (symbiosis)
– e.g., bacterial colonization of hyphal tips, suggests "freeloading" on fungal enzymes
• saprotrophs are very important in nutrient cycling
• many very good examples of fungal saprotrophy
– e.g., wood decay
Phanerochaetae chrysosporium, Tom Volk
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Brown rot
Symbiotic interactions
• often called symbioses (singular ‐ symbiosis)
• sustained interactions between 2 or more species
• three different ecological types:
1 mutualism
1.
‐ both partners benefit
2. commensalism
‐ one partner benefits, the effect to the other is neutral
3. parasitism
‐ one partner benefits, the other is harmed
Brown rot
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Mycorrhizae
• symbiotic relationship between fungi and plant roots
• present in all vascular plants
Mutualism
– with the exception of the Cyperaceae and Brassicaceae
• fungi
fungi are much better than plants at scavenging are much better than plants at scavenging
mineral nutrients from soil (e.g., N, P)
– hyphae have a higher surface area:volume than root hairs
– fungi are very good at mobilizing nutrients
• they barter these valuable nutrients for a share of the plant's photosynthate
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Vesicular arbuscular mycorrhizae (VAM)
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Vesicular arbuscular mycorrhizae (VAM)
• Intramatricular phase
• VAM are members of Glomeromycotina (Zygomycota)
• tend not to be host‐specific
• they are all obligate
h
ll bli
bi
biotrophs
h
• associate with ~90% of plants at all latitudes
arbuscule
vesicle
intramatricular hyphae
• Extramatricular phase
– many herbaceous species
– sphere of absorption up to 8 cm from root
– forms a network that supports multiple plants
– produce resting spores in soil
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Ectomycorrhizae
Ectomycorrhizae
• members of Eukarya (mostly Basidiomycota)
• Intramatricular phase
– exhibit a temporal succession with plant host
– early colonizers are not host‐specific
– later colonizers have greater host specificity
later colonizers have greater host specificity
– mantle
• loose to dense cap on hyphae on root
• sometimes can pull it off like a thimble
sometimes can pull it off like a thimble
• probably provides storage
• they are all facultative biotrophs
• associate with ~5% of plants, mostly temperate latitudes
– Hartig net
• proliferation of intercellular hyphae (not intracellular!)
• locus of nutrient exchange
– mostly associated with woody species
– conifers, oak, birch, aspen, etc. (but not maple)
Amanita colonising root tip
Wiki: http://www.biomedcentral.com/1471‐2105/6/178
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Lichens
Ectomycorrhizae
• Extramatricular phase
– creates a thick matt in upper soil layers
– thought to be a very long‐lived network
C t
Crustose
F li
Foliose
Squamulose
Fruticose
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http://www.waldeneffect.org
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D Malloch
Lichen asexual reproduction
Lichen sexual reproduction
Lecanora granti
Lichenomphalia umbellifera
D Malloch
D Malloch
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Lichens are polyphyletic
Lichen habitats
• saxicolous
– epilithic
– endolithic
Gargas A, PT DePriest, M Grube and A Tehler. 1995. Multiple origins of lichen symbioses in fungi suggested by SSU rDNA phylogeny. Science (cover article) 268: 1492‐1495
•
•
•
•
•
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tterricolous
i l
corticolous
epiphyllous
zoophilous
lots of others
LICHENS ARE VERY
SENSITIVE TO THE
ENVIRONMENT
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Leaf‐cutter ants
Leaf‐cutter ants
Annual Review of Microbiology Vol. 55: 357‐380, 2001
Gail Shumway/Getty Images
Currie CR. 2001. A community of ants, fungi, and bacteria: a multilateral approach to studying symbiosis Annual Review of Microbiology 55: 357‐380
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Malassezia yeasts
Commensalism
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Types of parasites
• Necrotrophic parasite
– kills host cell then consumes it
Parasitism
• Biotrophic parasite
– uses the living host cell without killing it
– can be:
• obligate biotroph
• facultative biotroph
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Modes of parasitism
Parasites & predators
• Contact parasites
– parasite produces an contact cell on host
Dicyma (●) parasitizing Fusicladium (○)
– does not perforate cell wall
Trop Plant Pathol 33:5‐11, 2008
– host cytoplasm unchanged, but ↓ growth rate
• Haustorial parasites
– perforate host cell with haustorium
– remains enveloped in host plasmalemma
– common in Mucormycotina
Piptocephalis freseniana on unknown host
Das Pflanzenreich Hausschatz des Wissens (1900)
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• grey area
• parasite typically reside directly on the host whereas predators stalk prey
• predators kill prey, but parasites don't always d
kill
b
i d ' l
kill their hosts
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Parasites & pathogens
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Powdery mildews
• "pathogen" does not describe an ecological role, rather it is the capacity of some agent to cause a disease state in an organism
• many proper ecological parasites do not act as many proper ecological parasites do not act as
pathogens (although some do)
• similarly, many organisms that may be commensals, mutualists or even saprotrophs
can be pathogens under certain circumstances 29
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Nematode trapping fungi
Competition
• Interspecific competition
– the struggle between different species to access the same resource in limited supply
– an outcome of niche overlap
an outcome of niche overlap
A
B
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George Barron
Types of competition
Defense
• Interference competition
– behavioural or chemical interaction between competitors that differentially limits the ability of one competitor to access the resource – the effect persists even when the antagonistic competitor th ff t
it
h th
t
i ti
tit
is no longer present
• Exploitation competition
– depletion of resource without reducing the ability of the competitor to access whatever of the resource remains
– typically driven by speed by which a competitor is able to secure the resource
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• fast growth & reproduction
• cell wall
– biochemistry
– morphological modifications (anti‐feedant)
h l i l
difi i
( if d )
• secondary metabolites
– oxalic adic crystals
– toxins
• lytic enzymes
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