Parasitism

Question 1

Define parasite

Answer 1

Consumes tissues/body fluids of host

BUT doesn’t kill host

Question 2

What are the 2 main types of parasite?

Answer 2

Endoparasite = in 
Ectoparasite = on

Question 3

Define pathogen

Answer 3

Microparasites that cause disease

- don’t directly consume host tissue

Question 4

Define parasitoid

Answer 4

Insects whose larvae feed on a single hot & kill it

Question 5

Describe parasite bodies & life cycles

Answer 5

Simple body

Complex life cycle

Question 6

What does malaria success depend on?

Answer 6

Surviving in 2 hosts
Developing into 3 diff life forms
Being transmitted correctly

Question 7

In order to complete their life cycles, some parasites can do what?

Give examples

Answer 7

Change host behaviour

Hairworm - induces water-seeking behaviour in terrestrial hosts = suicide

Zombie ants - infected with fungus move up to top of leaves & can’t move

Question 8

How can parasites improve their transmission?

Give examples

Answer 8

Alter host’s mating system

Silene/Mycobotrium - produces fungal spores instead of pollen & spreads like an STI via pollinators

Wolbachia - feminise males & cause females to become parthenogenic

Question 9

Which parasite is common in Red Grouse?

Answer 9

Nematodes

Question 10

Do nematodes cause cycles in Red Grouse populations?

Answer 10

In mathematical simulation:
Cycle amplitude decreased w/ increasing application of anti-nematode drugs

–> suggests nematode parasites shape grouse population densities

Question 11

What caused the decrease in American chestnut?

Answer 11

Parasite (Chestnut blight fungus) from China is not virulent on Chinese host
- but virulent on American species

Question 12

Parasites can alter the outcome of which type of interaction in a community?

Answer 12

Competition

Question 13

Define virulence

Answer 13

Harm done by a parasite to host following infection

Question 14

What is the conventional wisdom hypothesis?

Answer 14

Given enough time a state of peaceful coexistence eventually becomes established between any host & parasite

Question 15

What is the trade-off hypothesis?

Answer 15

Natural selection should favour the strategy that maximises pathogen individual fitness
= trade-off between rate of transmission & duration of infection

Question 16

What are the 3 types of transmission?

Answer 16

Horizontal
Vertical = mother –> offspring
Sexual

Question 17

Which type of transmission should favour higher virulence?

Answer 17

Horizontal

Question 18

Why’re waterborne pathogens more virulent the sexually transmitted pathogens?

Answer 18

Even if host is dead parasite can still be transmitted via water

Question 19

What does parasites reducing host fitness lead to?

Answer 19

Pressure on hosts to evolve response

e.g. their behaviour or immune responses

Question 20

Host-parasite interactions are likely to lead to what?

Answer 20

Coevolution

Question 21

In terms of loci, define arms race and trench warfare

Answer 21

AR = creating new loci

TW = changes in allele present at resistant loci

Question 22

What type of selection does Trench warfare impose?

Answer 22

Freq-dependent selection

–> maintains genetic variation

Question 23

Is it more likely that the coevolution of hosts & parasites occurs by trench warfare or arms race?

Answer 23

Trench warfarre
- high cost of keeping resistance & virulent genes
= high cost of more loci
–> prevents arms race

Question 24

Is there anyway to stop the coevolution process?

Answer 24

Tolerance traits
- reduce impact of parasites on host fitness

BUT doesn’t exert selection on parasite

Question 25

According to the trade-off hypothesis, virulence should be the result of what?

Answer 25

The optimal compromise between length of infection & growth to maximise transmission