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1
Variation in Traits Among Organisms
Time scalewithin lifetime of an individual
ontogeny (age dependent)
plasticity (environment dependent)
age
trait
over evolutionary time (between species)
Genotype 1differentphenotypes
Environmental cues or influences, during ontogeny
temperature, light,nutrients, crowding,predators
development
Phenotypic variation can be continuous
Developmenttemperature
Amountofpigment
Dorsal pigmentation in Drosophila
Genotype 1
Phenotype 1
OR variation can be discrete (only a few phenotypes)
development Phenotype 2
when variation is discrete, called “polyphenisms”
2
Pig-nosed turtle (Australia)Sex (male or female) depends on temperature
during development
http://aerg.canberra.edu.au/pub/aerg/images/turtles/htcaret.jpg
Can J Zool 82:1251-1257, 2004
males only
females only
Issues in Plasticity
What is the pattern? (how sensitive?)
Is the degree of plasticity genetically based?
Is plasticity adaptive?
[what are the developmental/physiologicalmechanisms?
age
trait
Trait score
environment
“norm of reaction”
genotype
differentenvironments
A graphical depiction
3
How plastic is size in relation to crowding?
Annie Schmitt et al., 2003
Impatiens capensis
Schmitt et al. 2003
uncrowded crowded
Plan
t si
ze
Is there genetic variation for plasticity?If so, can respond to selection and thus can evolve!
Multiple isogenic lines, grow in different environments & compare“norms of reactions”
Environment Environment
trai
t
effect of environment change isgenotype dependent
Nutrient level
Hea
d he
ight
dap
hnia Woltereck 1909, “reaktionsnorm”
Huge effect, but effects are genotype dependent(“genotype by environment interaction”)
Take multiple isogenic lines, grow in different environments & compare
Developmental temperature (°C)
Mea
n th
orax
siz
e (m
m)
19 25
1.04
1.05
1.06
1.07
1.08
1.09
Genetic variation for norms of reaction?Effect of egg-to-adult temperature on ADULT fly size
83% of organisms show this pattern bacteria, protists, plants, inverts, verts
4
low rearingtemperature
high rearingtemperature
Isofemale lines
egg
adult
Developmental temperature (°C)
Mea
n th
orax
siz
e (m
m)
19 25
1.04
1.05
1.06
1.07
1.08
1.09
Norms of reaction for temperature on fly sizeArtificial selection on degree of sensitivity -- select UP, select DOWN, + control
insensitive
sensitive
Developmental temperature (°C)
Mea
n th
orax
siz
e (m
m)
19 25
1.04
1.05
1.06
1.07
1.08
1.09 increased plasticity
control
decreased plasticity
data from Scheiner & Lyman, 1991
response after only 20 generations of selection on plasticityIs plasticity adaptive?
Physiological acclimation is one type ofplasticity, and is usually assumed to beadaptive (Dr. Pangloss is alive & well!)
But if go to extreme altitude,your physiology also changes,but for the worse! These shifts are pathological
Go from sea level to moderate altitudeinitially feel awful, then gradually feel betteras your physiology acclimates to altitude
These shifts are probably adaptive.
Photo Rainier
Photo K2
5
How can we test whether plasticity is adaptive ?
Environment A Phenotype X
Environment B Phenotype Y
transfer X & Y to Environment A, measure relative fitnesstransfer X & Y to Environment B, measure relative fitness
GENOTYPE 1
If plasticity is adaptive, who wins in Env. A (or in Env. B)?
Impatiens capensis
Schmitt et al. 2003
tall
short
uncrowded crowded
Plan
t si
ze
Shade-avoidance response incrowded conditions
photos Impatiens& Annie Schmitt
high density low density
May increase light interceptionin dense conditions
Don’t waste carbon onstems
Growth response to “crowding” in Impatiens
photos
Response is mediated physiologically by ratio of red:far red wavelengths of light chlorophyll absorbs red, so reduces R:FR
Phenotype manipulation: grow in different R:FR lightrelease in high or low density plots, measure fitness
density-dependent stem elongation is adaptive in Impatiens
Elongated plants have higher fitness than suppressed plants athigh density, but lower fitness at low density.
Susan Dudley and Annie Schmitt 1996, Am. Nat.
photos
6
Polyphenism inwing colorin Africanbutterflies
Bicyclus
Paul Brakefield
Photo courtesy ofPaulBrakefield,U. Leiden
The morphs are seasonal anddepend on temperature during development !
Wet season (hot) Dry season (cool)
sisters
Photos of butterflies in wet & dry seasonPhotos of habitats in wet & dry season
Hypothesis:
small eye spot enhances camouflagein dry season
Test:
rear the morphs in the lab (at diff. temperatures) releaserecapture
7
Adults are fruit-feeding
Can be trapped
Also numbered with pens
Photo ofbutterflies at
baits
Photoresearchertrappingbutterfiles
Data of Nico Reitsma
Reared at several differenttemperatures, generating rangeof morphs -- then released
Graph shows that dry season morph has muchgreater survival in dry season than do wetseason morphs
Small eye-spotted butterflies survived betterin dry season, but why?
small eye-spots advantageous?
some other factor changed bydevelopmental temperature?
Solution?
take dry-season morph, “paint” eye spotson some, compare survival !
control
sham
treatmentReared at low temperature,but painted eye spots on some &sham-painted others -- then released
8
Conclusion:
the small eye-spot morph is advantageousin the dry season, probably because it is relatively well camouflaged
(lab experiments support this)
But what about the big eye-spot morph in thewet season?
slight survival advantage, but not huge.Is not because of crypsis, but perhapspredator deflection or sexual selection ?
photos
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