Announcements

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BIOL223 Genetics Evolution March 25,
2009 Population Genetics Wed Adaptation and
Sexual selection Fri Sexual selection/overview

Announcements Reading Freeman Herron Today
and Friday Ch. 10 and 11 Homework HW 7 after
Spring Break HW 6 Key has been posted Take-home
exam posted today Practice exam posted yesterday
http//www.cbs.umn.edu/populus/ Review session,
T April 7th 530 7PM, HS207
Jumping spider Family Salticidae
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Adaptation
Hemeroplanes ornatus A sphinx moth
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Key Questions in Evolutionary Biology How do
you study adaptation? What limits the adaptive
process? How do different selective mechanisms
shape adaptive traits?
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• Testing hypotheses about adaptation
• Experimental approach
• Observational approach
• Comparative approach
• In all approaches, we test observations vs. the
  predictions of alternative evolutionary scenarios
  (and vs. the null hypothesis of randomness)

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Experimental approach to studying
adaptation Example Wing markings and
wing-display in Zonosemata flies
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Flies have dark wing bands, distinctive
wing-waving behavior. What is the adaptive value
of these traits? Jumping spiders are striped and
wave legs in territorial display Are flies
predator MIMICS like sphinx moth caterpillars?
HOST PLANT Solanum elaeagnifolium Silverleaf
nightshade
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• Testing hypotheses about adaptation
• Experimental approach
• Test observations vs. predictions of alternative
  evolutionary scenarios (and vs. the null
  hypothesis)

Hypothesis1 (H1) No mimicry. Many flies have
banded wings and flick them too! Possible
courtship display.
Hypothesis2 (H2) Flies mimic jumping spider to
ward off other predators that seek to avoid
jumping spiders (rather like sphinx moth)
Hypothesis3 (H3) Flies mimic jumping spider to
deter predation by jumping spiders.
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No extant Z. vittigera variants that lack wing
bands and wing-display How do we test for the
Ghost of Predation Past?
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Zonosemata vittigera
Mustica domestica
Create a variant, as clear-winged Z. vittigera do
not exist
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The predator line-up
Non-jumping spiders
Whip-tail lizard
Assassin bugs
Mantis
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Arthropod UFC The experimental apparatus
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Key details (1) Random presentation of test
flies to predators (2) Predators re-tested (3)
all exp treatments highly replicated
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A sheep in wolfs clothing
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Observational approach

• Sometimes evolutionary hypotheses are hard to
  test experimentally
• Make predictions that can be tested by observing
  behaviors/morphologies under natural conditions.

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Ex Behavioral thermoregulation in reptiles (Huey
et al.)
Ectotherms must regulate body temperature with
behavior (that is, seeking out warmer or cooler
places) Do they do this adaptively?
Endotherms
Body temp.
Dipsosaurus dorsalis
Ectotherms
Environmental temp.
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Performance as a function of ambient temperature
What does thermal performance look like in lab?
(Critical thermal max)
Variants who do this better may have increased
fitness
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Ex Garter snake thermoregulation Obs. 1 garter
snakes in lab perform best at 28-32 C Obs. 2
garter snakes maintain even temp. in wild
Huey et al. 1989
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Obs.3 Thermal profiles of available habitats
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Garter snakes
Obs.3 Medium rocks provide optimum range of
temperature conditions
Prediction If behaving adaptively, garter
snakes will choose to rest under medium rocks
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Do garter snakes behave adaptively (i.e., do
they choose to rest under medium rocks)?
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Comparative approach
Convergent evolution by distantly related
species is evidence for adaptation
Cactus (New World deserts)
Euphorbs (Old World deserts)
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Placental mammals Australian marsupials
Convergent matches between ecology
morphology/behavior in placental mammals vs.
marsupials
Niche
Burrower
Anteater
Mouse
Climber
Glider
Cat
Wolfe
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Comparative approach

Are tubular red flowers adapted for bird
pollination?
Mimulus cardinalis low elevation
Mimulus lewisii high elevation
Bradshaw Schemske (mid-1990s)
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Aquilegia (Columbines)
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Salvia (Sages)
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Costus (Gingers)
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Independent evolution of hummingbird
flowers Adaptation inferred from comparative
biology
Costus
Salvia
Aquilegia
monocots
dicots
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• Is everything an adaptation?
• Most organisms show phenotypic plasticity

• Expression of an organisms morphology, behavior,
  physiology, etc. may depend on its specific
  environment
• One manifestation
• so called norm of reaction

• Different genotypes may
• have different
• norms of reaction

• Sometimes, plasticity can be evolutionarily
  adaptive, i.e., have a heritable component

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Daphnia magna
Planktonic FW crustacean
exhibit phototaxis.
Reproduce sexually and parthenogenetically
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Daphnia exhibit negative phototaxis in the
absence of predators
But the degree to which they exhibit this
behavior depends on their experience of predators
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Daphnia eggs can survive for decades in lake
sediments (diapause)
So lake sediments contain a living record of
population genetic data
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Phenotypic plasticity for phototaxis has a
heritable component Tested Daphnia from
sediments of different age in man-made lake.
Cousyn et al. 2001 PNAS(USA) 986256-6260