Download Animal Behavior

What about the Population Bottleneck Scenario?
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Sequencing studies of MHC alleles in humans and chimpanzees show the existence of
many ancient polymorphisms in the human species
Because of balancing selection (selection favoring heterozygotes) at MHC loci, many
different alleles are maintained in a population and may persist for millions of years;
some alleles in chimpanzee are more similar to their homologs in humans than they
are to other alleles in the chimpanzee
Conclusion from MHC studies
• Population bottlenecks would act to greatly reduce allelic
diversity at the MHC loci. Evidence suggests that this is
not the case.
• Based on computer simulations, best estimate of the
minimum human population size of about 10,000
(minimum estimate is 500).
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New Topic: Animal Behavior
• Definitions
• Ethology
– The study of animal behavior in relation to the
natural environment; the ecology & evolution of
animal behavior
– Pioneering ethologists: Konrad Lorenz, Niko
Tinbergen & Karl von Frisch: first and only animal
behaviorists to win a Nobel prize (in physiology
and medicine, 1973)
• Psychology
– study of how behavior is modified by experience
through learning and memory
Two types of questions about
animal behavior
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How Questions = Proximate Questions:
– What are the mechanisms underlying behavior?
– How is the nervous system wired?
– What stimuli elicit a behavior?
– How do hormonal levels influence the development and
expression of the behavior?
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Why Questions = Ultimate Questions = Evolutionary Questions:
– What is the purpose or function of a behavior?
– How does the behavior affect the probability of survival
and/or reproduction of an individual
– What was the original step in the historical process that led to
the existence of a behavior
– How has the behavior evolved and how has it changed over
evolutionary time
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Part 1: How Questions
Part 2: Why Questions
(Behavioral Ecology)
Types of Behavior:
Instinctive vs. Learned Behaviors
• Instinctive Behaviors
– Behaviors which appear in fully functional form the
first time they are performed: The term “geneticallydetermined” is somewhat misleading
– Called Fixed Action Patterns (FAP) by ethologists
ß e.g., Web-building in spiders
ß Egg-rolling in geese
ß Pecking response in gulls
• Learning: the durable modification of behavior
in response to experience
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Where does behavior come from?
• In reality, most behaviors fall on a continuum
between innate (hardwired) and learned
• Even instinctive behaviors are influenced by the
environment in the sense that their expression is a
product of their genotype + development.
Testosterone has two effects on male
rat behavior
• Primary sexdetermining signal
stems from TDF on Y
• Organizational effect
on the development of
the brain when the
animal is very young;
• Activational effect
when the hormone
triggers sexual behavior
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Female Rat Sexual Behavior
• In absence of TDF,
ovaries develop and
testis regress
• Female fetus develops
under the influence of
estrogens (estradiol)
• Brain develops
estrogen receptors
• Maturing brain
develops mechanisms
for mating & maternal
behavior
Fetal Environment Influences Male
Aggressive Behavior
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Testosterone’s effects not all bad ...
How de we figure out whether
behaviors are instinctive or learned?
Deprivation experiments
• Many studies in laboratory
– Rear individuals in isolation to see if
they still exhibit the behavior
• Natural experiments
– Galah parrot & pink cockatoo
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Example of galah parrot and pink cockatoo
• Both species nest in tree holes in
Australia
• Sometimes the larger cockatoos eject
adult galahs from nest after egg laying
has taken place
• The cockatoos unwittingly rear galah
chicks
• Provides natural experiment to
investigate instinctive versus learned
behaviors
• Galah chicks give alarm call of galah
parents despite having been
completely isolated from other galahs
• By contrast, galah chicks learned
contact call of cockatoos
How de we figure out whether behaviors
are instinctive or learned?
Twin concordance studies:
• Concordance: The presence of a given trait in both members of a
pair of twins.
• In twin studies, researchers assess both members of identical
(monozygotic) and fraternal (dizygotic) twin pairs, who typically are
exposed to common environmental influences. If genes influence the
probability of exhibiting a particular trait, identical twin pairs, who
share the same genes, will tend to be concordant-that is, both will
exhibit or not exhibit the trait. Fraternal twin pairs, on the other hand,
are no more similar genetically than non-twin siblings, and so will be
less concordant - there will be more pairs in which one twin exhibits
the trait and the other does not. By comparing the degree of
concordance in identical and fraternal twins, researchers can
estimate the extent to which genes influence trait expression.
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How de we figure out whether
behaviors are instinctive or learned?
Reverse Genetics: The experimental procedure
that begins with a cloned segment of DNA, or a
protein sequence, and uses this knowledge to
introduce programmed mutations (through
directed mutagenesis) back into the genome in
order to investigate gene and protein function.
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fruitless Splicing Specifies
Male Courtship Behavior in Drosophila
• “Male courtship requires products of the fruitless (fru)
gene, which is spliced differently in males and
females. We have generated alleles of fru that are
constitutively spliced in either the male or the female
mode. We show that male splicing is essential for
male courtship behavior and sexual orientation.
More importantly, male splicing is also sufficient to
generate male behavior in otherwise normal
females. These females direct their courtship toward
other females … The splicing of a single neuronal
gene thus specifies essentially all aspects of a
complex innate behavior.” (From Cell, Vol. 121, 785–794,
June 3, 2005)
What factors favor instinctive (innate)
over learned behaviors?
• Short generation time
and absence of parental
care, e.g., insects,
spiders etc (no time for
learning)
• Expression of behavior
is appropriate in almost
every context: e.g.,
pecking response is
"feed me"
• Expression of behavior
has to be right the first
time, e.g., alarm calls;
predator avoidance in
moths and kangaroo rats
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How are Fixed Action Patterns (FAPs)
elicited?
Releaser: the specific stimulus required to
elicit a FAP
• Red bill spot in gulls: only a red spot on an
elongate rod is needed to elicit pecking
response in chicks
• Nut releases digging behavior in squirrels
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Red underside releases male
aggression in sticklebacks
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Learned behaviors
Learning: the durable modification of
behavior in response to experience
Types of learning I
Classical conditioning: studied by Pavlov;
involuntary activity becomes associated with
a stimulus
• Animal learns to associate involuntary activity with
a stimulus
• Repeated association of stimulus with reward or
punishment causes stimulus alone to elicit response
• Turn on light, give dog meat powder; dog salivates;
eventually light alone causes dog to salivate
• Occurs in organisms ranging from roundworms to
humans
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Types of learning II
Operant Conditioning: animal learns to
associate voluntary behavior with a stimulus
• Trial and error learning
• Skinner boxes
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Skinner: Reductio ad absurdum
• Thought much of
human behavior could
be reduced to operant
conditioning
• Built a Skinner Box
for his daughter
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Types of learning III:
biased learning
Behavioral Imprinting: form of learning in
which individuals exposed to certain key
stimuli early in development form a
lifelong association with the object
Konrad Lorenz's geese
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Nick Smythe's agoutis and pacas (large, Neotropical rodents)
By imprinting the paca on large social groups, Smythe was able to
domesticate the paca in one generation.
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