Parasitism Flashcards
Define parasite
Consumes tissues/body fluids of host
BUT doesn’t kill host
What are the 2 main types of parasite?
Endoparasite = in Ectoparasite = on
Define pathogen
Microparasites that cause disease
- don’t directly consume host tissue
Define parasitoid
Insects whose larvae feed on a single hot & kill it
Describe parasite bodies & life cycles
Simple body
Complex life cycle
What does malaria success depend on?
Surviving in 2 hosts
Developing into 3 diff life forms
Being transmitted correctly
In order to complete their life cycles, some parasites can do what?
Give examples
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
How can parasites improve their transmission?
Give examples
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
Which parasite is common in Red Grouse?
Nematodes
Do nematodes cause cycles in Red Grouse populations?
In mathematical simulation:
Cycle amplitude decreased w/ increasing application of anti-nematode drugs
–> suggests nematode parasites shape grouse population densities
What caused the decrease in American chestnut?
Parasite (Chestnut blight fungus) from China is not virulent on Chinese host
- but virulent on American species
Parasites can alter the outcome of which type of interaction in a community?
Competition
Define virulence
Harm done by a parasite to host following infection
What is the conventional wisdom hypothesis?
Given enough time a state of peaceful coexistence eventually becomes established between any host & parasite
What is the trade-off hypothesis?
Natural selection should favour the strategy that maximises pathogen individual fitness
= trade-off between rate of transmission & duration of infection
What are the 3 types of transmission?
Horizontal
Vertical = mother –> offspring
Sexual
Which type of transmission should favour higher virulence?
Horizontal
Why’re waterborne pathogens more virulent the sexually transmitted pathogens?
Even if host is dead parasite can still be transmitted via water
What does parasites reducing host fitness lead to?
Pressure on hosts to evolve response
e.g. their behaviour or immune responses
Host-parasite interactions are likely to lead to what?
Coevolution
In terms of loci, define arms race and trench warfare
AR = creating new loci
TW = changes in allele present at resistant loci
What type of selection does Trench warfare impose?
Freq-dependent selection
–> maintains genetic variation
Is it more likely that the coevolution of hosts & parasites occurs by trench warfare or arms race?
Trench warfarre
- high cost of keeping resistance & virulent genes
= high cost of more loci
–> prevents arms race
Is there anyway to stop the coevolution process?
Tolerance traits
- reduce impact of parasites on host fitness
BUT doesn’t exert selection on parasite
According to the trade-off hypothesis, virulence should be the result of what?
The optimal compromise between length of infection & growth to maximise transmission
