Download 06_GeneticsBehavior1

Genes vs. Environment?
Cake analogy…
recipe + ingredients
= cake
genes + environment = trait
Is a cake more recipe or more ingredients?
Is the difference between 2 cakes due to differences
in the recipe or ingredients?
Natural Experiment:
Cross-fostering of galah chicks by pink cockatoos
Which species will the galahs behave like?
Are behaviors results of social environment or
genetic input?
Depends on the behavior…
Begging calls galah
Alarm calls galah
Contact calls cockatoo
Flight pattern cockatoo
Food preference cockatoo
galah
pink cockatoo
Categorization of Behaviors:
Innate
Learned
Begging calls
Contact calls
Alarm calls
Flight pattern
Food preference
Learned Behaviors
Studied by behaviorists (Skinner)
Modified by specific experiences
Two main types of associative learning…
Classical Conditioning
Famous example of Pavlov’s dogs
Conditioning of response (salivation) by
association of the unconditioned stimulus (food)
with a conditioned stimulus (bell)
(Basis for successful advertising)
Operant Conditioning
Association of voluntary activity with the
consequences that follow (Skinner box)
Can have positive and negative reinforcement
Basis of dog training!
Operant Conditioning
After a behavior is performed:
Add a
stimulus
reinforcement
+
(food)
punishment
_
(shock)
Remove a
stimulus
Effect
_
Increases
behavior
(alarm clock)
+
(grounded)
Decreases
behavior
Basics of operant condition
(Dog Training 101)
The reinforcement must follow the desired behavior
within 1 sec (with one exception…).
Negative reinforcement must be consistent to
extinguish a behavior.
Inconsistent positive reinforcement only increases the
frequency of the behavior!
Limitations/exceptions of operant conditioning
Nausea as punishment is effective even hours after
the behavior and administered only once.
Ultimate explanation for this?
Some combinations of behaviors and consequences
can not be associated
Innate/instinctive behaviors
Studied by ethologists (Tinbergen, Lorentz)
Appears fully formed the first time it is performed
Usually triggered by a simple cue…
Pecking behavior by gull chicks
Fixed Action Pattern (FAP): Any innate behavior
that gets carried to completion once triggered by a
cue.
Sign stimulus or releaser: the cue that initiates a
FAP
Yawning
FAP and releaser
Consistent in length and appearance
Difficult to stop once started!!
Susceptible to cheaters..
Rove beetle & ant
Beetle larvae produce ant
pheromone, releasing “take
to brood chamber” behavior
Also get fed by stimulating
regurgitation behavior in
workers, both as larvae and
as adults
Supernormal Stimulus
More effective releaser of behavior than biologically
correct stimulus
Previous example of long stick with dot releasing
begging in gull chicks
Many examples in nature and is basis for one
theory on male ornamentation.
Genetics of Behavior
How to measure the genetic component of behavior.
1) Control environmental variation
2) Similarities between relatives & non-relatives
3) Selection experiments
4) Modern techniques.
Heritability (H2): the proportion of variance in a trait
attributable to genetic variation.
Phenotype, Genotype, Environment
P = G + E + (G x E)
H2 = VG / VP
VG
H2 =
VG + VE + V (G x E)
1) Control Environmental Variation
By raising genetically variable individuals in the
same environment, we can estimate amount of
phenotypic variation that is genetic (VG).
Do the same in very different environments to
estimate total phenotypic variance (VP).
How do we measure the environmental component of
a behavior (VE)?
Raise individuals that are genetically similar in
different environments.
Norm of reaction: range of phenotypic variation for a
single genotype resulting from environmental
differences.
Migration routes of blackcap warbler
populations:
Change in blackcap warbler migratory behavior in
Britain in 1950’s prompted investigations into the
genetic control of migration.
Hypothesis 1: Birds over-wintering in Britain had lost
ability to migrate.
Test: See if birds caught in Britain in winter and their
offspring raised in lab show same pre-migratory
activity as German birds raised in lab.
Result: They do show the same activity
Conclusion: Hypothesis 1 not supported, birds have
not lost their migratory activity.
Hypothesis 2: Birds over-wintering in Britain have a
genetic difference which causes them to migrate in a
different direction
Test: Check migratory direction of offspring of British
birds and German birds reared in the same
laboratory conditions.
Results:
Conclusions: Appears to be a genetic difference in
migratory behavior.
Why have western mutants not arisen in other
populations?
Another test of the genetic basis hypothesis:
Cross birds from
southwestern Germany
(brown arrows) to birds from
Austria (white arrows).
Offspring (blue arrows) flew
in intermediate direction!
2) Similarities between relatives and non-relatives:
Parent-offspring comparisons
Twins, full-sibs, and half-sib comparisons
But don’t forget about influence of similar
environment!! Identical twins reared apart – opposite
of controlled environment studies
Coefficient of Relatedness: the proportion of
alleles, on average, that two individuals
share.
C.R.
Identical (monozyotic) twins
Parent-offspring
Fraternal (dizygotic) twins
Full siblings
Half siblings
Step siblings
non-relatives
1
0.5
0.5
0.5
0.25
0
0
IQ studies in humans
Hypothesis: Differences in IQ scores are caused by
differences in genes ONLY
Conclusions?
3) Selection Experiment
In a behaviorally variable population, only allow
certain individuals to reproduce.
If the differential reproduction results in a change in
the behaviors in the population, then there MUST be
genetic variation associated with the behavioral
variation!
The speed of the change gives an indication of how
much of the behavioral difference was due to genetic
differences
Nest building behavior in mice
1) Measure the amount of cotton used by mice to
make nests.
2) Create a “high” line with mice that used lots of
cotton, “low” line with mice that used little cotton,
and “control” line of mice picked at random.
3) Continue selection (within each line) over
several generations.
Other selection experiments:
flight speed in Drosophila
calling behavior in crickets
Are there genes for behaviors?
“anxiety and aggression” gene?
http://www.sciencedaily.com/releases/2003/01/030123072840.htm
“alocholism” gene?
Gene Linked To Alcoholism Alcoholism tends to run in families,
suggesting that addiction, at least in part, has an underlying
genetic cause. Now, researchers at the University of Illinois at
Chicago have discovered a gene linked to alcohol dependency.
Laboratory mice deficient in the gene were found to consume
excessive amounts of alcohol, preferring ethanol to water and
evincing highly anxious behavior in a maze test.
Drunken Fruit Flies Reveal Molecular Pathway Regulating
Sensitivity To Alcohol (June 17, 1998) -- Researchers at UC
San Francisco have identified a molecular pathway in intoxicated
fruit flies that is responsible for regulating the flies' meandering,
wobbling responses to alcohol.
http://www.sciencedaily.com/releases/2004/05/040526063645.htm
CNN
Pinker says it's nature, not nurture. Genes, instincts
determine thoughts, feelings, behavior
According to Steven Pinker, every human
exclamation, every chuckle, every expression of love
stems not from life experience, but from millions of
years of human development.
http://www.cnn.com/2004/WORLD/americas/04/16/pinker/index.html
CNN
Caution urged for brain research on violence
Research into brain patterns linked to violent behavior is
important, but should be approached with caution. "The
research ... provides a window into the many factors that
influence behavior. Early experiences are important but
not necessarily fixed."
http://archives.cnn.com/2000/HEALTH/07/28/violent.brains/index.html
'Mood Genes: Hunting for Origins of Mania and
Depression' By Samuel H. Barondes
“sitter” and “rover”
Drosophila larvae
True-breeding
parents
“sitter” and “rover”
Drosophila larvae
True-breeding
parents
F1 = all rovers
F2 = 3:1
rovers:sitters
“larval feeding behavior” gene: dg2
cGMP-dependent protein kinase
Alleles = enzyme variants with different
catabolic efficiencies
Produced only in cells in olfactory system and brain
Affects reception and assessment of
environmental cues?
Changes in nervous system producing locomotion
4) Modern methods for finding genes that influence
behavior:
Induced-mutation experiments:
Mutate individuals, look for variation in behavior,
then figure out which gene was mutated to cause
change
Knock-out experiments:
Inactivate a specific gene, then look for any
changes in behavior
4) Modern methods for finding genes that influence
behavior:
QTL mapping:
Using many markers (quantitative trait loci)
throughout genome to identify chromosome
region(s) that correlate with behavior.
Gene expression (microarrays):
Quantify variation in gene expression among
individuals performing different behaviors.
Additivity or dominance: the effect of one allele on
another allele at the same genetic locus.
Epistasis: the effect of one genetic locus on
another independent locus.
Pleiotropy: the effect of a single gene or two or
more phenotypic traits.
Polygenic: the effect of two or more genes on a
single phenotypic trait.
Phenotypic plasticity: the interaction between
genetic factors and the environment (e.g, norm of
reaction).
Genomic Imprinting
Effects (gene products) of a gene differ depending
on whether inherited from mother or father
What fitness benefit is gained by changing gene function
depending on the parent it’s inherited from?
Hypothesis: Benefits stems from conflict between the
parents over investment in the offspring.
Mothers may reduce investment in current offspring
to invest in future offspring, while father only cares
about current offspring, because mother’s future
offspring may not be his.
Proximate studies: genetic variation for behavioral
variation is maintained.
Ultimate studies: why is genetic variation
maintained if selection usually acts to decrease
variation!?!
One of the biggest unanswered questions - what
maintains genetic variation in traits under strong
selection.
Proximate studies: genetic variation for behavioral
variation is maintained.
Ultimate studies: why is genetic variation
maintained if selection usually acts to decrease
variation!?!
Fitness benefits of genetic variants are not
constant, but depend on environment, and the
environment is variable?
Back to rovers and sitters – why are there
two feeding strategies?
Hypothesis: Sitting is best strategy at low
densities, while roving is best in high densities.
Test: Raise random sets
of larvae in different
environments and
measure average
movement after several
generations.