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Symbioses - Mutualism
Symbioses
• Symbioses - species living in close
association
• Parasitism +,- parasite benefits, host harmed
• Commensalism +,0 or 0,0 can have positive
effect for one species or for neither
• Mutualism +,+ both species benefit
Mutualism
• Definition - the
individuals in a
population of each
mutualist species grow
and/or survive and/or
reproduce at a higher rate
when in the presence of
individuals of the other.
Each benefits (+,+)
General Features of Mutualisms
1. The life cycle of most mutualistic species is very simple
(in contrast to parasites)
2. There is no conspicuous dispersal phase for most
endosymbionts (endomutualists)
3. Populations of most mutualists are stable in size - no
epidemics as seen in parasites
4. The ecological range (niche breadth) of organisms in
mutualisms usually appears to be greater than that of either
species alone
5. Host specificity is usually flexible
6. Within populations of mutualists, the number of
endosymbionts per host is relatively constant
Two types of Mutualism
• Facultative - each partner gains a benefit but
is not dependent on the other - the vast
majority of mutualisms are facultative.
• Obligate - one or both partners is dependent
on the other and cannot survive without the
other.
Mutualisms Involving Links
in Behavior
Greater Honeyguide
Honey Badger
Ants and Acacia Trees
Beltian bodies (yellow) on Acacia leaves
Ant larvae inside Acacia “horn”
Pollination Mutualisms
Pollination syndromes
among the phloxes
Honeybee
covered with
pollen
Honeybee
pollinating
beebalm –
Monarda sp.
With visible light
with UV light
Nectar guides for honeybees
Cyrtid fly
pollinating
a composite
Caralluma – carrion fly pollinated
Erysimum – butterfly pollinated
Hummingbird pollination
Greater double-collared sunbird
Episcia – moth pollinated
Bat pollination
Hammer Orchid and Wasp
Figs and Fig Wasps
Figs and Fig Wasps
Mutualisms involving Culture of
Crops or Livestock
Leaf-cutter Ants – genus Atta
Diagram of Leaf-cutter ant colony nest
Human Agriculture
Sustainable Dairy
Industrial Wheat
Digestive Mutualisms Involving
Gut Inhabitants
Ruminant with multiple stomachs
Ruminant by-products
Termite Mound Western Australia
Termites
Mycorrhizae
Ectomycorrhizae
Ectomycorrhizae
VAM – Vesicular Arbuscular Mycorrhizae
Nitrogen Fixing Mutualisms
Red Clover – A Classic Legume
Normal Nitrogen Fixation
Legume Root Nodules
Rhizobium root nodules on a bean plant
Animal-Algae Mutualisms
Healthy Coral Reef - Indonesia
Coral polyp with zooxanthellae
- a dinoflagellate, Symbiodinium
Coral polyp – coral animal is green,
Zooxanthellae is red
Endosymbiotic Origin of Eukaryotes
Lynne Margulis
Endosymbiotic Origin of Eukaryotes
Endosymbiotic Origin of Eukaryotes
• The earliest eukaryotes acquired mitochondria by
engulfing alpha proteobacteria.
• The early origin of mitochondria is supported by the fact
that all eukaryotes studied so far either have mitochondria
or had them in the past. Mitochondria have their own
DNA and replicate themselves during cell division.
• Later in eukaryotic history, some lineages of heterotrophic
eukaryotes acquired an additional endosymbiont—a
photosynthetic cyanobacterium—that evolved into plastids.
• This hypothesis is supported by the observation that the
DNA of plastids in red and green algae closely resembles
the DNA of cyanobacteria.
• Plastids in these algae are surrounded by two membranes,
presumably derived from the cell membranes of host and
endosymbiont.
Stromatolites on coast of Western Australia