Lecture 18

Question 1

Phenotype

Answer 1

• Any observable characteristic or trait of an organism including morphology, physiology, behavior

Question 2

Phenotypes reflect both genetic and environmental effects

Answer 2

• Z = G + E
• Z: phenotype, G: genes, E: environment

Question 3

Extending notion of phenotypes

Answer 3

• Evolution by natural selection
  
  • Variation in a trait
  • Genetic basis for the trait
  • Variation in fitness for the trait

Question 4

What is fitness for a parasite

Answer 4

• R0: The # of new infections generated by a single infected individual
• Depends on things like replication or growth within the host, opportunities for transmission between hosts

Question 5

Parasite extended phenotypes

Answer 5

• Three broad categories of extended phenotypes in parasites
  
  • Host behavioral modification
  • Host morphological modification
  • Host molecular modification
• Aim to increase fitness of parasite

Question 6

Three hypothesis

Answer 6

• Adaptive for parasite: generates a fitness benefit to parasites that led to natural selection for trait
• Adaptive for host: generates a fitness benefit to hosts that led to natural selection for trait
• Coincidental by-product of infection

Question 7

How to find a parasite adaptation

Answer 7

• Is there a benefit?
• Is phenotype specific? Does it only occur in presence of parasite and are benefits specific to that parasite
• What is timing of this manipulation
• How does strength of manipulation change
• How complex is the trait
• What do comparative analyses suggest

Question 8

Toxoplasma gondii

Answer 8

• When rodents are infected:
  
  • More active
  • Explore more
  • Less likely to startle
  • More aggressive over territories
  • Slower reaction times

Question 9

Behavioral manipulation by Toxoplasma gondii

Answer 9

• When rats are infected, they are attracted to cat urine
• When mice are infected: increase neural activity in posterodorsal medial amygdala (involved in innate reproductive behavior)
• Cysts accumulate in brain of infected rodent over time. More cysts = more dopamine

Question 10

Fungal infections in ants

Answer 10

• Ants infected with multiple species of fungi turn into zombies that engage in death grips on vegetation

Question 11

Parasite adaptation or not

Answer 11

• Specificity: does the behavior only occur in presence of parasite
  
  • Yes, uninfected ants are found in trees, while all infected ants are found low to the ground

Question 12

Experiment: Moved infected ants to ground or canopy

Answer 12

• In canopy: fungus failed to grow normally and never produced a stroma
• On ground: 14 of 16 ants disappeared in <24 hours
• Clear fitness costs to fungus of different ant death locations

Question 13

Malaria parasites and vector feeding behavior

Answer 13

• Part 1: Mosquitoes recently exposed to malaria(not yet infectious) reduce feeding behavior
• Part 2: When infectious, malaria-infected mosquitoes are more persistent in feeding attempts

Question 14

Experiment: In addition to malaria, expose mosquitoes to non-infectious challenge to see if behavior changes in this context too.

Answer 14

• Part 1: Reduced feeding behavior of mosquitoes is not specific to malaria infection, though response is stronger
• Part 2: Increased feeding behavior of mosquitoes is maybe specific to malaria infection. (heat killed E.coli group goes in same direction, need more study)

Question 15

Malaria parasites and host attractiveness

Answer 15

• Hosts infected with transmissible forms(gametocytes) attract more mosquitoes

Question 16

Parasite adaptation or not

Answer 16

• Mosquitoes are also attracted to infectious mouse hosts
• Healthy host made to smell more like infectious hosts: mosquitoes prefer them
• Infectious hosts are made to smell more like healthy hosts: mosquitoes avoid them