Transcript 15Molles5e

Mutualism
Chapter 15
1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Outline
•
•
•
•
Introduction
Plant Mutualisms
 Mycorrhizae
 Ants
Coral Mutualisms
Evolution of Mutualisms
2
Introduction
•
Mutualism: Interactions between individuals of
different species that benefit both partners.
 Facultative Mutualism occurs when a
species can live without its mutualistic
partner.
 Obligate Mutualism occurs when a species
is dependent on a mutualistic relationship.
 Margulis and Fester amassed evidence
eukaryotes originated as mutualistic
associations.
3
Plant Mutualisms
•
Two most common types of mycorrhizae:
 Arbuscular mycorrhizal fungi (AMF)
 Produces arbuscules - site of exchange
between plants and fungi, hyphae fungal filaments, and vesicles - energy
storage organs.
 Ectomycorrhizae (ECM)
 Forms mantle around roots - important in
increasing plant access to phosphorus
and other immobile nutrients.
4
Mycorrhizae and Plant Water Balance
•
Allen and Allen studied water relations of
grass Agropyron smithii.
 Plants with mycorrhizae maintained higher
leaf water potentials.
 Plants with greater access to
phosphorus may develop roots that are
more efficient at extracting and
conducting water.
5
Mycorrhizae and Plant Water Balance
•
Hardie suggested mycorrhizal fungi improve
water relations by providing more extensive
contact with moisture in rooting zone and
providing extra area for water absorption.
6
•
•
Nutrient Availability and Mutualistic
Balance Sheet
Johnson investigated whether fertilization
can select for less mutualistic mycorrhizal
fungi.
 Fungal partner received an equal or
greater quantity of photosynthetic product
in trade for low quantity of nutrients.
In nutrient poor environments, many plants
invest disproportionately in roots.
 Found higher root investment in low N
soils.
7
Nutrient Availability
•
•
Results suggested mycorrhizal fungi from
unfertilized soils supplied plants with more
nutrients.
 Plants able to invest more energy in
above-ground photosynthetic material.
Found Andropogon produced inflorescens
only in nitrogen-supplemented treatments.
8
Nutrient Availability
9
Ants and Swollen Thorn Acacia
•
•
Herbivores attempting to forage on accacia
plants occupied by accacia ants are met by
a large number of fast, agile, highlyaggressive defenders.
Ant Benefits:
 Thorns provide living space.
 Folliar nectaries provide sugar.
 Beltian bodies are a source of oils and
protein.
10
Ants and Swollen Thorn Acacia
11
Experimental Evidence For Mutualism
•
Janzen demonstrated ants significantly
improve plant performance.
 Acacias without ants had more
herbivorous insects.
 Suckers growing from accacia stumps
occupied by ants lengthened at seven
times rate of suckers without ants.
 Suckers with ants survived at twice the
rate of suckers without ants.
12
Temperate Plant Protection Mutualism
•
•
Ants are attracted to Aspen sunflowers
because they produce nectar at extrafloral
nectaries.
 Rich in sucrose and amino acids.
Inouye and Taylor never observed several
species of ants collecting nectar from aspen
sunflower blossoms nor tending aphids.
 Extrafloral nectaries sufficient attractant.
13
Temperate Plant Protection Mutualism
•
•
Proposed ants may protect sunflower’s
developing seeds from seed predators.
 Damaged over 90% of seeds produced by
some flowers.
 Flowers without ants suffered 2-4 times
more seed predation.
Relationship remains facultative.
 Every few years flower heads of aspen
sunflowers are killed by late frost.
14
Temperate Plant Protection Mutualism
15
Coral Mutualisms
•
Zooxanthallae and Corals
 Zooxzanthallae live within coral tissues.
 Receive nutrient from coral. In return,
coral receives organic compounds
synthesized by zooxanthallae during
photosynthesis.
 Corals induce release of organic
compounds with “signal compounds”
that alter permeability of
zooxanthallae cell membrane.
16
Coral Mutualisms
•
•
Corals also control rate of zooxanthallae
population growth and density by influencing
organic matter secretion.
Main zooxanthallae benefit appears to be
access to higher nutrient levels, especially N
and P.
 Uptakes ammonium excreted by coral.
17
Coral Protection Mutualism
•
Glynn found 13 coral species protected by
crustacean mutualists.
 Crustacean mutualists substantially
improved chances coral will avoid attack
by sea stars.
18
Coral Protection Mutualism
•
Also found crab activity promotes coral
health and integrity.
 Pocillopora coral increases production of
fat bodies in the presence of crabs.
 Digestive tract of crabs inhabiting corals
contained large quantities of lipids.
19
Evolution of Mutualism
•
Theory predicts mutualism will evolve where
the benefits of mutualism exceed the costs.
 Keeler developed models to represent
relative costs and benefits of several types
of mutualistic interactions.
 Successful mutualists
 Give and receive benefits.
 Unsuccessful mutualists
 Give, but do not receive benefit.
20
Evolution of Mutualism

•
Non-mutualists
 Neither give nor receive benefit.
For a population to be mutualistic, fitness of
successful mutualists must be greater than
unsuccessful or non-mutualists.
 If not, natural selection will eventually
eliminate the interaction.
21
Facultative Ant-Plant Mutualisms
•
Keeler proposed for a facultative ant-plant
mutualism to evolve and persist, proportion
of plant’s energy budget ants save from
destruction by herbivores must exceed
proportion of the pant’s energy budget
invested in extrafloral nectaries and nectar.
22
Facultative Ant-Plant Mutualisms
•
Conditions that may produce higher benefits
than costs:
 Low proportion of plant’s energy budget
invested in extrafloral nectaries.
 High probability of attracting ants.
 Low effectiveness of alternate defenses.
 Highly effective ant defense.
23
Review
•
•
•
•
Introduction
Plant Mutualisms
 Mycorrhizae
 Ants
Coral Mutualisms
Evolution of Mutualisms
24
25