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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

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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

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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

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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

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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