definitions and predictions types of exchange between

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

Pollination Mutualism

pollinator angiospermnutrients

gametetransport

Seed Dispersal Mutualisms

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seedtransport

Disperser Angiospermfruit

carbohydrates



Endosymbiosis: a protist-algal mutualism

Vorticellaprotist

phagocytosis Chlorellagreen alga

endosymbiosis

photosynthate

essential mineralnutrients

Leaf Cutter Ants and Fungal “Farms”



Atta mexicana



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)



Theobroma cacao

nutritionCacao Endophyte

pathogen defenseGrasses

nutrition

herbivory defense



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)





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





Algal Infection and Release

Sachs and Wilcox (2006)

Infected polyps Uninfected polyps

Free algae

ephyramedusa

Does infection mode influence mutualism?


Verticaltransmission

Horizontaltransmission

Free algae

Measure Host and Symbiont Fitness


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



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



Partner ChoiceRepeated Interactions



Alignment of Interests



Restrictions of Options



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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increased resistance to wildtype strain

Redman, Dunigan, Rodriquez 2001

increased drought resistance

increased growth

Plants Colonized by Mutualist Strain Have:

definitions and predictions types of exchange between

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