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Lecture Outline
Definitions and Predictions
Types of Exchange Between Partners
Examples
Exploitation of Mutualisms
Examples
Stabilizing Mechanisms
Case Study: What is the difference between
a parasite and a mutualist?
Symbiosis
(Greek: with life)
An intimate and exploitative, neutral, or beneficial
interaction between different species
Mutualism
A reciprocally beneficial interaction between different
species
Cooperation or mutual exploitation?
Continuum of Interactions
(-,+)
(o,+)
Predation
Parasitism
Commensalism
(o) = no net gain or loss (neutral)
(+) = net gain (beneficial)
(-) = net loss (exploitative)
(+,+)
Mutualism
Species 1 Population Size
Population Trajectories With and Without Mutualism
With Species 2
Without Species 2
Species 2 Population Size
Time
With Species 1
Without Species 1
Time
Obligate Mutualism
Species 1 Population Size
Population Trajectories With and Without Mutualism
Positive Interaction
Coefficient
dN1 r1N1 (K1 − N1 + α12 N 2 )
=
K1
dt
Species 2 Population Size
Time
dN 2 r2 N 2 (K 2 − N 2 + α 21N1 )
=
K2
dt
Time
Mutualism Categories
TRANSPORT
What is exchanged?
Plant-pollinator
Plant-dispersal
PROTECTION
NUTRITION
Ant-acacia
Gut symbioses
Lichens
Plant-fungal
mycorrhizae
Plant-fungal
endophytes
Plant-rhizobia
Marine-dinoflagellates
Eukaryotes-organelles
Pollination Mutualism
nutrients
pollinator
angiosperm
gamete
transport
Seed Dispersal Mutualisms
seed
transport
Disperser
fruit
carbohydrates
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Angiosperm
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Endosymbiosis: a protist-algal mutualism
photosynthate
Vorticella
phagocytosis
protist
Chlorella
green alga
essential mineral
nutrients
endosymbiosis
Leaf Cutter Ants and Fungal “Farms”
nutrition
Ants
nutrition
Fungi
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Atta mexicana
Fungal mycelia
consuming
harvested foliage
Lichen: Fungi and Green Algae or Cyanobacteria
fruticose
protection
Fungi
Algae
carbohydrates
thallus cross-section
Fungal Endophytes and Plants
nutrition
Cacao
pathogen defense
nutrition
Endophyte
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Theobroma cacao
Arnold et al (2003)
herbivory defense
Grasses
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Festuca
Clay (1988)
When Mutualisms Get Ugly…
Beneficial interactions are susceptible to exploitation
from inside and outside the interaction
(+)
Species 1
Species 2
(+)
Cheating
from inside
interaction
Exploitation
from outside
interaction
Arboreal Ants and Whistling Thorn Acacia in Kenya
Defense leads to
parasitism
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Ants
(+)
shelter and
nutrients
Acacia
(-)
Acacia drapanolobium
C. mimosea
C. sjostedti
C. nigriceps
T. penzigi
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vulnerable to canopy take-over
40% increase branch in production causes tree
sterilization, but reduces lateral contact with
other trees
Stanton et al (1999)
Shift to Predation
Excess sugar
Predation (8x)
carbohydrate
(+) Ants
Aphids (+,-)
Waste removal, predator protection
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Offenberg (2001)
Algal Infection and Release
medusa
ephyra
Free algae
Infected polyps
Uninfected polyps
Sachs and Wilcox (2006)
Does infection mode influence mutualism?
Free algae
Vertical
transmission
Horizontal
transmission
Sachs and Wilcox (2006)
Measure Host and Symbiont Fitness
HOST FITNESS
Reproduction (count buds)
Polyp growth rate
SYMBIONT FITNESS
Reproduction (expulsion rate)
Algal density within host
Sachs and Wilcox (2006)
Symbiont Reproduction
Algae faces tradeoff
Maximizing algal reproduction
reduces host growth rate
and expulsion
Host Growth Rate
Shift to parasitism limits
spread of algae to new host
Cleaner and Client Fish Mutualism: Partner Choice Simulation
“Resident Client”
2nd
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1st
“Choosy Client”
The cleaner fish maximized food intake in all trials and identified the
“choosy client” option after 1 simulation
Bshary and Grutter (2002)
If mutualism fails in one population, other
cooperating populations can repopulate
(+,-)
(+,+) (+,-)
(+,-)
(+,-)
(+,-)
(+,+)
(+,-)
(+,-)
(+,+)
(+,-)
(+,-)
(+,-)
(+,+)
Extinction
(+,+) (+,+) (+,+)
(+,+)(+,+)
(+,-)
(+,+)
(+,+)
(+,+)
(+,-) (+,+)
(+,+)
(+,+)
Success
Thompson (2005)
Summary of mutualism stabilizing mechanisms
Vertical Transmission
Restrictions to Fitness
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Partner Choice
Repeated Interactions
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Restrictions of Options
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Alignment of Interests
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Colletotrichum spp.
UV
Wildtype:
Pathogen
100% lethal
to host plant
Mutant:
Commensal
No effect on
host plant
UV
Mutant:
Mutualist
Benefits host
plant
Redman, Dunigan, Rodriquez 2001
Plants Colonized by
Mutualist Strain Have:
increased resistance to
wildtype strain
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increased drought
resistance
increased growth
Redman, Dunigan, Rodriquez 2001