BIOL 290 Lecture Notes - Lecture 17: Crab Louse, Frequency-Dependent Selection, Head Louse

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Published on 12 Dec 2018
Cholera: in humans
Link between outbreak of disease and environment
Regularity between outbreaks of disease
Host is trying to outcompete parasite
Strong interaction/ competition between host and parasite
Batarchochytrium dendrobatidis (Bd)
Fungus that came from somewhere in Asia
Severe; almost hundreds of species extinct
Amphibian apocalypse
Host Parasite Coevolution
Head louse
Evolved together; each trying to get upperhand
Head louse; where we got the expressions "nit-picking" and
"feeling lousy"
Humans have three species of louse that attack them; head lice and
pubic lice; got our pubic louse from gorillas, and head lice from
chimps, and louse that can grab onto our close
Tight connection between evolution of host and parasite
Flowers and bees
Hypotheses about parasite-host coevolution
1. Negative frequency dependent selection
Disease strains that are successful in exploiting the most common
host types would also become more common, thus the rare host
types are less affected.
Sneaking salmon; interaction where what one species does effects
the other one
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2. Red Queen Hypothesis
An evolutionary arms race; sexual reproduction would allow for
rapid variation in a host population under interaction with a
parasite with fast-pace mutations
Infinite race between one strategy against another
3. Trade off between transmission and virulence
A highly virulent parasite can produce many offspring in a short
time, but killing the host quickly reduces its lifespan, thus reducing
potential for transmission
Trade off between the 2 is necessary; leading to decrease in
virulence; a constant transmission potential and increase the host's
Very virulent vs transmission; if you are not a good disperser, may
want to be less virulent; if you are good at dispersal; short lifespan
doesn't matter
The study of distribution and causes of health states in populations,
and use of this study to address health related problems
Modern epidemiology considers diseases as a 2 species interaction
(parasite and host) or multi-species system
Cholera epidemic: London 1854
Influenza 1918
Younger people had higher mortality than older people
People think that older people might have been survivers of
another epidemic before this; allowing them to develop immunity
to the older strain, and help them survive this new strain
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