Lecture 18

Question 1

Define extended phenotypes and use beaver dam building as an example

Answer 1

Phenotypes (visible morphology/behaviour/physiology) that exists past the individual

Beavers have a gene that interacts with the environment to either produce large or small dams in rivers; beavers with the genes that induces large dam building should have a higher fitness because they are more likely to survive

Question 2

What is R(0)? What does it depend on? (3)

Answer 2

The number of new infections generated by a single infected individual in a fully susceptible population (what pathogens aim to optimize)

Depends on:
Replication within a host
Growth within a host
Opportunities for transmission between hosts

Question 3

Extended phenotype categories (3)

Answer 3

Host behaviour modification
Host morphological modification
Host molecular modification

Question 4

What behavioural manipulation occurs when toxoplasma gondii infects mice? Who does this benefit at the cost of whoelse?

Answer 4

Infect mice -> mice become more active/aggressive/explore more

This behaviour benefits the parasite (so it can be transmitted and infect cats) at the cost of the mice (who are prey to cat)

Question 5

Selection Hypotheses (3)

Answer 5

Adaptive for the parasite (benefit parasite fitness)

Adaptive for the host (benefit host fitness)

Coincidental by-product of infection (beneficial side effects)

Question 6

What was the conclusion to the toxo infected mouse study where mice were enclosed in an area and attraction to a urine smell was observed to measure extended phenotype behaviour?

Quickly explain the results

Answer 6

The parasite was expressing its phenotype through the mouse as moving toward the urine smell did not benefit the mouse

Uninfected mice headed toward the rabbit smell, infected mice headed toward the cat smell

Question 7

What was the conclusion to the ant fungal infection study where zombie ants were moved and fungal growth was observed to measure extended phenotype expression?

Quickly explain the results

Answer 7

Parasites took over the actions of the ant to move it to where it would benefit it’s (parasite’s) growth

When ants were moved to the ground they went missing, to the canopy there was unusual growth

Question 8

How long does a malaria parasite’s life cycle take? What are the two periods and what major event occurs during each?

Answer 8

Half of the life cycle (10-14 days) is spent either inside or outside the human host or the mosquito host

Two periods: 
Incubation period (mosquito starves itself as feeding could damage the fragile vector) 
Mature period (mosquito gets aggressive and is now ready for transmission)

Question 9

Is the infected mosquito starving character specific for malaria?

Answer 9

No—any perturbation to the Mosquitos immune system causes it to reduce feeding behaviour

Question 10

What was the conclusion to the infected mosquito attraction study where infected individuals were given a choice host and attraction was observed?

Quickly explain the results

Answer 10

Parasite affects the smell of the vector (mosquito) to attract it toward certain things

Some infected mice attracted to both infected and uninfected hosts equally while some were more attracted to infected infectious hosts