Mutualism: So What Is It Anyway?

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Mutualism:
So What Is It Anyway?
Eric Ribbens
Western Illinois University
1
In The Garden
Joel and Lisa were exploring a garden. They
sniffed appreciatively at blooming lavender,
pulled petals from a white daisy (“he loves me,
he loves me not …”)
and whistled back
at a killdeer running
away, wing drooping.
Joel stooped over to
peer at an odd plant.
2
3
Ants and Aphids
“What are those ants DOING?” Joel asked.
Lisa stared too. “It
looks like they are
aphid farmers.”
“Aphid farmers?
Huh?”
4
Ants and Aphids
Lisa pointed. “Look here! This ant is collecting
honeydew from the aphid. It’s basically plant sap, rich
in sugar. The ant eats it after the aphid sucks it from
the plant.”
Joel shuddered. “No way I’m sucking honey from
someone’s butt!”
5
Ants and Aphids
Lisa laughed. “Nope, but that’s what ant farmers
do. They take care of the aphids, carry them
around, and protect them. In turn, they get food
from the aphids.”
Joel nodded eagerly.
“So that would be
an example of … what
did my odd biology
professor call it …
a mutualism?”
6
Mutualism
Lisa smirked. “You mean you actually
remember something from that class? What
else do you know about mutualisms?”
Joel frowned. “Hey, I got a C! Well, a C-.”
“Yeah, so you’re not God’s gift to biology.
You’re stalling …”
7
Mutualism
Joel scowled. “Hmm. Two species interacting in
a way that benefits one of the species …”
Shaking her head, Lisa corrected “No! That’s
commensalism. Mutualism benefits both
species.”
“And isn’t there something about cymbals or
something like that?”
“You mean symbiosis. An interesting word.”
8
Symbiosis
“Sym means with. Think symphony … sounds
with other sounds. Biosis means life. So
symbiosis means living with another species.”
Joel nodded vigorously. “Like these ants and
the aphids. But don’t the aphids also live with
the plant? That’s not a mutualism, is it?”
9
Symbiosis ? Mutualism
“Good point,” agreed
Lisa. “And interestingly,
a rather common
confusion. Come on,
let’s go to the library. I
want to show you
something.”
10
At the Library
Lisa started pulling textbooks from the shelves.
Joel turned the computer on.
“What are you doing?” Lisa asked.
“Getting ready to search the internet, of
course!” Joel replied. “I love Wikipedia!”
“Huh? Real knowledge only comes in books!”
snorted Lisa.
11
The Textbooks
Lisa flipped through a biology textbook. She
read:
“Mutualism: an interaction between two species in
which both benefit from the association.”
“Symbiosis: in a broad sense, the living together of
two or more organisms of different species; in a
narrow sense, synonymous with ‘mutualism’.”
12
The Internet
Joel frowned. “That’s not what you just said!
But read here: This webpage has it wrong too!”
Symbiosis is defined as: "the intimate living together
of two dissimilar organisms in a mutually beneficial
relationship.” http://www.flickr.com/people/symbiosis/
13
Lisa agreed. “What does Wikipedia say?”
Joel typed. The screen showed:
“The term symbiosis (from the Greek: σύν syn "with";
and βίωσις biosis "living") commonly describes close
and often long-term interactions between different
biological species. The term was first used in 1879 by
the German mycologist Heinrich Anton de Bary, who
defined it as "the living together of unlike
organisms."[1][2]
14
Symbiosis : Mutualism?
Lisa said, “So this nicely shows the controversy.
Is symbiosis another name for mutualism, or is
it a completely different concept?”
Joel said absently, “Why would you want two
terms that mean the same thing? It makes
more sense for mutualism to mean both
benefit, and symbiosis to mean living together.
But can symbiosis not be mutualisms?”
15
Lisa said “The plural of symbiosis is symbioses,
dummy. Good question. Can you think of an
example of a symbiosis that is not a mutualism?”
“What about malaria?
The malaria, um,
protistans, live in your
blood, but they sure
don’t give you a
benefit!”
16
Is it Science?
Joel sighed. “How can I be expected to learn
something when the experts can’t even
agree?”
Lisa punched him. “You know that scientists
are people! They make mistakes too. But
science is so powerful because it ends up
selecting the ideas that are supported by
evidence. This is just science in process!”
17
How Did They Evolve?
“I remember something else,” Joel murmured.
My bio prof kept insisting that evolution is one
of the great ideas of science. But how could
these different kinds of interactions evolve?”
Lisa nodded vigorously. “A great question!
Remember that evolutionary theory says that
every species will tend to develop traits that
increase the ability of that species to survive.”
18
Evolutionary Predictions
“Yeah, but that’s my point. How could some
of these interactions develop, and wouldn’t
you expect them to change over time?”
19
Two-Species Interactions
• Research time! What are the categories of
possible interactions between two species,
and how are the different categories defined?
20
Next Question
• Should symbiosis refer only to mutualisms?
Should mutualism and symbiosis mean the
same thing?
21
Credits
Slide 2
Description: Bee on daisy
Author: Tony Wills
Link: http://commons.wikimedia.org/wiki/File:Fly_on_daisy_02.jpg
Clearance: Creative Commons Attribution-Share Alike 3.0 Unported license.
Slide 3
Description: Ant Lasius flavus and aphids Fordinae
Author: Nbharakey
Link: http://commons.wikimedia.org/wiki/File:Ant_Lasius_flavus_and_aphids_Fordinae.jpg
Clearance: Public domain.
Slide 4
Description: Ant cultivating aphids
Author: Fir0002
Link: http://commons.wikimedia.org/wiki/File:Ant_cultivating_aphids.jpg
Clearance: Creative Commons Attribution-Share Alike 3.0 Unported license.
Slide 5
Description: Aphids visited by black garden ants (Lasius niger) and brimming over with honeydew.
Author: Jens Buurgaard Nielsen
Link: http://commons.wikimedia.org/wiki/File:Aphids_with_honeydew_and_ants.JPG
Clearance: Creative Commons Attribution-Share Alike 3.0 Unported license.
Credits cont.
Slide 6
Description: Ant guards its aphids.
Author: ViaMoi
Link: http://commons.wikimedia.org/wiki/File:Ant_guards_its_Aphids.jpg
Clearance: Creative Commons Attribution 2.0 Generic license.
Slide 10
Description: Woman retrieving book at San Diego City College
Author: Joe Crawford from Moorpark, California, USA
Link: http://commons.wikimedia.org/wiki/File:SanDiegoCityCollegeLearingRecourceCity-bookshelf.jpg
Clearance: Creative Commons Attribution 2.0 Generic license.
Slide 16
Description: Young girl suffering of cerebral malaria. Coming from a remote village; she was referred to the main hospital in
Cotonou, Benin.
Author: WHO/Benoist Carpentier
Link: http://www.who.int/malaria/world_malaria_report_2009/photos/en/index.html
Clearance: Used in accordance with terms of use as stated on the image source page, link above.
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