Download Biology 312: January 5, 1999

Biology 360: January 24, 2007
Development of behavior 2
I.
What causes individuals of the same species to exhibit distinctly different behaviors?
This is where we can discuss the extent to which differences seen are the result of genetic
differences vs. environmental differences, and also the nature of those environmental
differences. My approach is to explore the different experimental methods used to
address this question.
NOTE: Make sure you know/understand the basics of the experiment, including the
basis experimental manipulations or observations, any controls if described and/or
comparisons made, and what the researchers actually measured)) to the level
presented in class/text (whichever is more detailed, if included in the text). You
should also be able to summarize the key results, and explain whether the key
results suggest a primarily genetic basis or a primarily environmental basis (or a
mix of both for the differences seen among individuals of a species.
A.
B.
C.
Hybridization
1.
What are hybrids?
2.
How are hybrids used to determine whether behavioral differences have a
genetic basis?
a)
General prediction: If there is a strong genetic basis for a
behavioral difference, then hybridization should produce a
stereotypical result with minimal variation among experiments.
3.
Example 1: Cricket song (Hoy and Paul) [Fig. in PowerPoint only]
4.
Example 2: rover vs. sitter Drosophila [Fig. 3.19]
Artificial selection
1.
What is artificial selection?
2.
How can artificial selection techniques be used to determine whether
behavioral differences have a genetic basis?
a)
General prediction: If the behavioral differences have a strong
genetic basis, you can create strains that reliably display the
behavioral characteristic you were attempting to select.
3.
Example 1: Selection for mice that collect either a particular large amount
or a particularly small amount of cotton for their nests [Fig. 3.24]
4.
Example 2: Selection for crickets with short vs. long calling times over
four generations [Fig. in PowerPoint only]
Inbred strains
1.
What are inbred strains?
a)
Closely-related individuals are bred over several generations.
2.
How are inbred strains used to determine whether a behavior is largely
genetically based?
a)
Compare inbred strains to each other, and to the population as a
whole. Strain-specific behavior patterns, specifically less
variability in behavior for strains compared to the population
suggest a genetic component for behavioral differences seen.
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3.
II.
III.
Example 1: Anti-predator response of two different strains of paradise
fish exposed to a model predator with eyes ([Fig. in PowerPoint, 1st pair of
bars]
4.
Example 2: garter snake food preferences [Fig. 3.21]
5.
How are inbred strains used to determine the role of environment?
a)
Examine inbred strain(s) (or artificially-selected strains) in
different environmental conditions. Similarity in responses of the
different strains to particular environmental stimuli suggests an
environmental basis for the differences seen.
6.
Example 1: Anti-predator response of two different strains of paradise fish
[Fig. in PowerPoint, 2nd pair of bars]
D.
Family relatedness studies (focused on twins)
1.
How are studies of twins used to determine the relative genetic and
environmental components of a behavior?
a)
If behavioral differences are primarily genetically based…

The correlation between identical twins (MZ) should be???

The correlation between fraternal twins (DZ) should be???

The correlation between parents and offspring (P-O) should
be???

The correlation between unrelated siblings (i.e. adopted
sibs) should be???
b)
If behavioral differences are primarily environmental, the level of
relatedness should not show any pattern. Rather, there should be
strong correlations between individuals brought up in the same
environment.
2.
Examples: Verbal ability in humans [Fig. 3.16]
E.
Creation/manipulation of mutant strains
1.
Prediction: If a single gene alteration can significantly alter a behavior,
behavioral differences are likely to have strong genetic basis.
2.
Example: oxytocin and male memory of females [Fig. 3.18]
Developmental Homeostasis
A.
Defined: The ability of individuals with genetic defects or with only minimal
exposure to appropriate environmental stimuli to develop nearly normally.
B.
Classic experiments: Harlow’s experiments with isolated rhesus monkeys, called
“social isolation experiments” [Fig. 3.27]
C.
Potential causal factors
1.
Redundancy (i.e. similar genes that overlap in function)
2.
Default programming
3.
NOTE: We won’t go into this more, since they really don’t get into much
more than the fact that it does occur. I think the examples about symmetry
really don’t say anything about developmental homeostasis.
Developmental switch mechanisms
A.
Overview: Phenotype that develops depends upon environmental conditions
(polyphenism = multiple phenotypes are possible)
B.
Example 1: tiger salamander larvae [Fig. 3.33]
1.
Two types (described)
2.
Under what conditions do Type 2 larvae develop?
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C.
3.
Advantages to environmentally-determined cannibal development
Example 2: Dung beetle males (not in text—I wasn’t impressed with the cichlid
example that was similar)
1.
“Resident” male appearance and behavior
2.
Sneaker male behavior
3.
Female behavior
4.
What determines whether a male will have horns or be a sneaker?
a)
External environmental factors
b)
Internal environmental factors
c)
Advantages to remaining hornless
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