3: Kiers et al 2003

Question 1

who can symbionts indirectly benefit?

Answer 1

competitors sharing the same host

Question 2

what can soybeans ‘punish’ and why?

Answer 2

rhizobia tat fail to fix N2 inside root nodules

Question 3

in the experiment what did they prevent condition wise?

Answer 3

mutualistic rhizobium strain prevented from cooperating

- replaced air with N2 free atmosphere so cant fix N2

Question 4

what did non-cooperation do to reproductive success of rhizobia

Answer 4

reduced it by 50%

Question 5

what are possible sanction against cheating rhizobia?

Answer 5

• decreased O2 supply and other resources needed for growth

- directly attacking rhizobia

Question 6

what do many mutualisms involve?

Answer 6

multiple symbiont genotypes per host

Question 7

how does the tragedy of the commons apply?

Answer 7

symbiont selected to increase its own growth and fitness at a cost to the host and other lineages
- symbionts as a group obtain more resources but not evolutionary stable as each lineage gains by being selfish

Question 8

what does rhizobia fix in the legume mutualism?

Answer 8

N2 in root nodules of host plant which is needed for growth and photosynthesis but costly

Question 9

what rhizobia will the plant favour?

Answer 9

the cooperative rhizobia- those that invest little into N2 fixation and will impose sanctions on others

Question 10

how may nodule level sanctions be reduced?

Answer 10

if cheat sharing nodule with mutualists