Parasitism 2

Question 1

what do parasites do to hosts

Answer 1

Pressure to evolve response

Question 2

How do parasites put pressure on hosts

Answer 2

changes in behaviour

and immune response

Question 3

What do host-parasite interactions affect

Answer 3

evolution of both species, leading to coevolution (evolving in response to one another), hosts always evolving to be less available to parasites and vice versa

Question 4

2 ways co-evolution can occur

Answer 4

Arms race- creation of new loci, constant evolution of new ‘weapons’ ie new mechanisms to attack parasite/host
OR by changes in allele present at resistant loci (Red Queen)

Question 5

what may prevent the arms race

Answer 5

cost of resistance and virulence

Question 6

Red Queen hypothesis

Answer 6

New genotype in host (a), increases in frequency, and parasites that can resist it (Va), increase in frequency, so hosts with (a) genotype begin to decline

Question 7

Frequency dependent selection

Answer 7

maintains genetic variation, and perhaps explains sexual recombination because new, beneficial gene combos are scrambled when passed onto the next gen which may be seen as a disadv, but parasites evolve so quickly that they’d be resistant already to the new genotype

Question 8

Tolerance traits

Answer 8

reduce impact of parasites on host fitness, Does not exert selection on/kill parasites
Thought of as a way to stop coevolutionary process

Question 9

commensalism

Answer 9

Individuals of one species benefit, while individuals of the other do not benefit and are not harmed

Question 10

Cleaner fishes- commensalism or mutualism?

Answer 10

Initially believed to be commensalism, cleaner fish clearly benefit but no clear benefit to hot fish.
Shown that without cleaners, host fish have more parasites, suggests its a mutualism

Question 11

Example of real commensalism

Answer 11

Anemone’s tentacles produce poison to kill small fish, clownfish can live there so fish gains protection but anemone no benefit

Question 12

symbiosis

Answer 12

relationship in which 2 species live in close physiological contact with each other, such as corals and algae

Question 13

symbioses include

Answer 13

parasitism, commensalism and mutualism

Question 14

benefits of mutualistic associations incl

Answer 14

nutrients, protection/defense, reproduction/dispersal

Question 15

human and bacteria mutualism

Answer 15

more bacteria in the body than human cells

Most are commensalists or mutualists-some don’t benefit humans, can become opportunistic

Question 16

Rhizobium example- nutritional mutualism

Answer 16

nitrogen fixing bacteria in legumes

bacteria gets carbohydrates from the plant, plant gets nitrogen from bacteria for growth

Question 17

Fungus farming ants

Answer 17

Ants collect leaves and take to their nest but don’t eat them, feed to the fungus.
Fungus able to digest cellulose grown on mushed leaves. Ants eat fungus
Seen as a parisitism originally but after studying molecular biology showed relationship ongoing and tightly co-evolved so fungus depends on ant for existence, therefore form of mutualism as fungus does benefit

Question 18

Ants and Acacias- example of protection mutualism

Answer 18

highly specialized
Acacia trees lack chemical defences, ants defend tree because ants raise young inside tree spines and produce high protein food to feed ants
Ants don’t eat acacia but eat everything around the tree- creates a clearing, reduces competition.
Remove ants- more herbivory- ants actively defend trees and make their leaves last longer

Question 19

Reproduction mutualism example

Answer 19

Pollinators
Plants get ovules fertilised
Animals get pollen or nectar as food
shapes specialised to pollinators

Question 20

If plants can self-fertilise why have pollinators?

Answer 20

self fertilising does not give an increase in genetic variation
Outcrossing may incr fitness in the presence of herbivores

Question 21

Dispersal mutualisms, big seeds example

Answer 21

Seeds don’t travel unless another organism eats/moves it

Question 22

What can parasitism/mutualism depend on

Answer 22

environment