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206-10lec...
Section 6.5
Research on fruit
flies shows that
natural selection
can act to maintain
two alleles at a
stable equilibrium
When frequency of p is
lower than its equil'M
value (0.6), it moves up
toward equil'M in next
generation
When frequency of p is
greater than its eq. value
(0.6), it moves back down
toward equil'm in next
generation
Unstable equilibria means that if the frequency of one
allele e ver gets above its initial frequency (say 0.8), then
it
should quickly rise to 1.0 (fixation). Likewise, if the
frequency of that allele e ver dips below 0.8, it should
quickly fall to zero. One alle le tends to go to fixation
while
the other allele is lost (unlike stable equilibria -->
both
alleles maintained, always go TOWARD equilibria point,
whereas unstable they always go AWAY equilibria point)
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12: Frequency MattersFebruary-05-10
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red = overdominance
blue = underdominance
This example is drawn right in 4th edition ( this is wrong?)
Crowding and ammonia resistance in fruit flies
Flies have access at top layer (b/c they need to breathe)
This morph appeared in crowding experi ments
Research on fruit
flies shows that
natural selection
can act to maintain
two alleles at a
stable equilibrium
when
heterozygotes have
superior fitness.
What about when
homozygotes have
superior fitness
instead?
Unstable equilibria means that if the frequency of one
allele e ver gets above its initial frequency (say 0.8), then
it
should quickly rise to 1.0 (fixation). Likewise, if the
frequency of that allele e ver dips below 0.8, it should
quickly fall to zero. One alle le tends to go to fixation
while
the other allele is lost (unlike stable equilibria -->
both
alleles maintained, always go TOWARD equilibria point,
whereas unstable they always go AWAY equilibria point)
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Warning colors -i'm toxic!
They are not necessarily the freak that stands out against other
drab individus
Even if they are distasteful, they will try to eat it
Association btwn frequency and color -want warning colors that
are univresal
and widespread - look at me but dont touch me
Hoverfly = tasty, safe to eat
Looks remarkedly similar to toxic wasp
This yellow and black theme is unive rsal as warning color
Frequency depe ndence? If mimic becomes too common,
predator still goes around and samples it (safe) , so if
mimic
cheats and becomes too common, the advantage goes
away
Need a balance where mimic ex itsst in lower frequencies
than model
Mullerian -reinforcing
Monarch tastes bad, viceroy is tasty
Viceroy is actuallly worse - not batesian, therefore mullerian
(b/c both taste bad)
Mimic movie -mi ra sorvino
Cockraoches spreading d isease.
She invents new bug termite,
praying mantis, cocroach,
(mixture of these)
piranhas
Yellow - more common than purple (60% yellow)
Why? Whats teh advatnage of having 2 colormorhps
It doesnt make nectar! Attracts bee, gets pol len stuck to
it, so flies to purple one b/c it knows yellow is a cheat
Then after purple, goes after yel low --> ping pong
2 morphs -ex tend trickery - get bees to visit more than
one flower
They mimic a nectar-giving flower
Means bees are
visiting yellow
flowers when they
are rare
Some species is pollen limiting
When yellow is rare -i t has advantage for female
Frequency dependence
Mimic on nectar providers, 2 morphs within it
Aposympamtic
Common is good, fitness is related ne gativily to being rare
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