lect 21 - symbiosis & parasitism

Question 1

conflict between hosts and symbionts

Answer 1

since there are fitness consequences for hosts taking care of symbionts, could hv cases where symbionts are selected to take more nutrients and replicate more — this would cause conflicts

pea aphids have extensive genetic variation in the ability to regulate symbiont numbers

symbiont load and fitness are negatively correlated— more symbionts = longer it takes for aphids to reproduce

conflict where symbiont genotype wants to replicate more and more

Question 2

host regulation of symbionts — example of aphids

Answer 2

STUDY: when more Buchnera in aphids, aphids take longer to reproduce

Question 3

what conditions would result in pathogens evolving to be MORE virulent or LESS virulent ?

Answer 3

STUDY/example: Rabbits and myxoma virus

— myxoma virus was lethal to rabbits when introduced
— it co-evolved and became milder in order to not completely wipe out its hosts
— the virus then came back much harder, having worse effects and dying much faster
RED QUEEN HYPOTHESIS

TRANSMISSION OF THESE VIRUSES very important !! what drives evolution
— too virulent = wasnt being transmitted to other hosts bc all died

• since the virus evolved to be an intermediate virulence, rabbits were able to gain immunity
  —-> virus came back harder to counteract this - RED QUEEN

Question 4

follow up study to rabbits and myxoma virus

Answer 4

ongoing arms race between evolution of virus and wild rabbits

1) Release of highly virulent virus
2) Evolution of reduced (intermediate)
virulence (not binine but reduced)
3) Evolution of host resistance
4) Evolution of acute virulence
5) then what ?