definitions and predictions types of exchange between
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Lecture Outline
Definitions and Predictions
Types of Exchange Between PartnersExamples
Exploitation of MutualismsExamplesStabilizing Mechanisms
Case Study: What is the difference betweena parasite and a mutualist?
MutualismA reciprocally beneficial interaction between different
species
Symbiosis(Greek: with life)
An intimate and exploitative, neutral, or beneficial interaction between different species
Cooperation or mutual exploitation?
Continuum of Interactions
(-,+) (+,+)(o,+)
PredationParasitism
Commensalism Mutualism
(o) = no net gain or loss (neutral)(+) = net gain (beneficial)(-) = net loss (exploitative)
Sp e
cies
1P
o pul
atio
n S
ize
Sp e
cies
2 P
opu l
atio
n S
ize
Time
Time
Population Trajectories With and Without Mutualism
Without Species 2
With Species 2
Without Species 1
With Species 1
Obligate Mutualism
dN1
dt=
r1N1(K1 −N1 +α12N2)K1S
p eci
es 1
Po p
ulat
ion
Siz
eS
p eci
es2
Pop
u lat
ion
Siz
e
Time
Time
dN2
dt=
r2N2(K2 − N2 +α21N1)K2
Positive Interaction Coefficient
Population Trajectories With and Without Mutualism
Mutualism Categories
NUTRITION Ant-acacia
Gut symbioses Lichens
Plant-fungal Plant-fungalmycorrhizae endophytes
Plant-rhizobia
Marine-dinoflagellates
Eukaryotes-organelles
PROTECTION
What is exchanged?TRANSPORT
Plant-pollinator
Plant-dispersal
Seed Dispersal Mutualisms
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seedtransport
Disperser Angiospermfruit
carbohydrates
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Endosymbiosis: a protist-algal mutualism
Vorticellaprotist
phagocytosis Chlorellagreen alga
endosymbiosis
photosynthate
essential mineralnutrients
Leaf Cutter Ants and Fungal “Farms”
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Atta mexicana
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Fungal mycelia consuming harvested foliage
nutritionAnts Fungi
nutrition
Lichen: Fungi and Green Algae or Cyanobacteria
fruticose
thallus cross-section
protectionFungi Algae
carbohydrates
Fungal Endophytes and Plants
Clay (1988)Arnold et al (2003)
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Theobroma cacao
nutritionCacao Endophyte
pathogen defenseGrasses
nutrition
herbivory defense
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Festuca
When Mutualisms Get Ugly…
Beneficial interactions are susceptible to exploitation from inside and outside the interaction
Species 1 Species 2(+)
(+)
Cheating from insideinteraction
Exploitation from outsideinteraction
Arboreal Ants and Whistling Thorn Acacia in Kenya
Stanton et al (1999)
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Defense leads to parasitism
Ants Acaciashelter and
nutrients(+) (-)
Acacia drapanolobium
C. mimosea
C. nigriceps T. penzigi
C. sjostedti
40% increase branch in production causes tree sterilization, but reduces lateral contact with other trees
vulnerable to canopy take-over
Shift to Predation
Offenberg (2001)
Excess sugar
Ants
Predation (8x)
Waste removal, predator protection
Aphids(+) (+,-)carbohydrate
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Algal Infection and Release
Sachs and Wilcox (2006)
Infected polyps Uninfected polyps
Free algae
ephyramedusa
Does infection mode influence mutualism?
Sachs and Wilcox (2006)
Verticaltransmission
Horizontaltransmission
Free algae
Measure Host and Symbiont Fitness
Sachs and Wilcox (2006)
HOST FITNESSReproduction (count buds)
Polyp growth rate
SYMBIONT FITNESSReproduction (expulsion rate)
Algal density within host
Algae faces tradeoff
Host Growth Rate
Sym
bion
t Rep
rodu
ctio
n Maximizing algal reproductionreduces host growth rateand expulsion
Shift to parasitism limitsspread of algae to new host
Cleaner and Client Fish Mutualism: Partner Choice Simulation
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Bshary and Grutter (2002)
“Choosy Client”
“Resident Client”
The cleaner fish maximized food intake in all trials and identified the “choosy client” option after 1 simulation
1st
2nd
(+,+)
(+,-)
(+,+)(+,+)
(+,+)
(+,+) (+,+)
(+,+)(+,+)
(+,+)
(+,+) (+,+)
(+,-)
(+,-)
(+,+)
(+,+)
(+,+)
(+,+)(+,-)(+,-)
(+,-)
(+,-)
(+,-)
(+,-)
(+,-)(+,-)
(+,-)
If mutualism fails in one population, othercooperating populations can repopulate
SuccessExtinction
Thompson (2005)
Summary of mutualism stabilizing mechanisms
Vertical TransmissionRestrictions to Fitness
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Partner ChoiceRepeated Interactions
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Alignment of Interests
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Restrictions of Options
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Colletotrichum spp.
UV UV
Wildtype:Pathogen
Mutant:Mutualist
Mutant:Commensal
100% lethalto host plant
No effect on host plant
Benefits hostplant
Redman, Dunigan, Rodriquez 2001
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