BIOL 290 Lecture Notes - Lecture 17: Crab Louse, Frequency-Dependent Selection, Head Louse
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Published on 12 Dec 2018
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Coevolution
• 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
• Amphibians
• 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
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
lifespan
• 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
• Epidemiology
• 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