Mutualism & Cooperation
What is the evolutionary "tragedy" faced by symbionts in a mutualistic relationship?
The Tragedy of the Commons
What gas mixture was used to mimic rhizobial "cheating" by preventing nitrogen fixation?
Argon:Oxygen (Ar:O2)
What is the differentiated, nitrogen-fixing form of rhizobia called?
Bacteriods
True or False: Mutualisms could sanctions help evolutionarily stabilize a wide range of mutualisms, especially those with multiple symbiont strains per host
True
This type of interaction where one organism benefits while the other is unaffected is often mistaken for mutualism.
What is commensalism?
What is the evolutionary puzzle that the legume-rhizobium mutualism helps explain?
Explaining mutualistic cooperation between species
At what three spatial scales were the rhizobia forced to cheat in the experiments?
Whole plants, half root systems, and individual nodules
True or False: Cutting off oxygen supply could impose sanctions on undifferentiated rhizobia but not bacteroids.
False, it could affect both forms
The results support what hypothesis about legume behavior towards non-fixing rhizobia?
That legumes impose sanctions/punishments on rhizobia that fail to fix nitrogen
In the honeyguide-human mutualism example, this term describes when one partner tries to get the benefit without doing its part of the cooperative behavior.
What is cheating?
What is the "Tragedy of the Commons" problem in the context of mutualisms?
Each symbiont lineage is selected to increase its own fitness selfishly, at the expense of the host and other lineages
How was rhizobial fitness measured in the different experiments?
By counting rhizobial colony forming units in nodules, on roots, and in surrounding sand/solution
True or False: A decrease in photosynthate supply appeared to limit respiration more in non-fixing nodules.
False
Besides sanctions, what other mechanisms could favor cooperative behavior in mutualisms?
Selection to associate with better cooperators, indirect mechanisms
Buchnera bacteria living inside aphid guts and providing essential amino acids exemplify this type of mutualism where both partners rely on each other for survival.
What is obligate mutualism?
What is the hypothesis proposed to stabilize mutualisms with multiple symbiont strains per host?
The "sanctions" hypothesis that hosts punish less cooperative symbiont behavior
What was the other name for soybean that was used in the experiments?
Glycine max
What plant resource showed decreased allocation to non-fixing nodules, potentially sanctioning the rhizobia?
Oxygen supply/nodule mass
What field in the world of business does the "sanctions" concept draw from?
Economics and/or social theory
Ants defend certain plants from herbivores by living in specialized hollow structures on the plants called these.
What are domatia?
What is meant by "horizontal transmission" in the context of mutualisms?
Transmission of symbionts between unrelated host individuals
What nitrogen-fixing bacteria species was used to inoculate the soybean plants?
Bradyrhizobium japonicum
What physiological parameter decreased in non-fixing nodules within 48 hours, implicating it as a sanctions mechanism?
Nodule interior oxygen concentration and nodule oxygen permeability
The paper suggests sanctions could stabilize mutualisms when what condition applies?
When there are many symbiont strains per host
This term describes interactions where the mutualistic relationship provides some fitness benefit under certain conditions, but is not absolutely required for survival of either partner.
What is facultative mutualism?