Download Document

Chapter 3
Development of Behavior
 Development
is an interactive process in
which the genes are turned on and off
both in response to environmental change
and simultaneously creating change.
 This
demonstrated by changes in behavior
shown by honeybees over the course of
their lives.
Development of Behavior
 Honeybees
when they emerge as adults
first work at cleaning cells then as they
age they shift to other tasks.
 Eventually
at about age 3 weeks they
begin foraging outside the hive.
Development of Behavior
 As
the bee goes through these changes in
behavior it appears that predictable
changes in the genes being actively
expressed occur.
 Microarray
technology makes it possible to
scan for activity levels of many genes by
detecting mRNA made when genes are
turned on.
Development of Behavior
 Comparisons
of arrays of nurse and
forager bees shows substantial differences
in genes turned on at each stage.
(YN= young nurses, OF = older foragers)
Development of Behavior

Transition to worker role appears to be strongly
influenced by level of a hormone called juvenile
hormone, which is produced by a gene.

The juvenile hormone gene turns on apparently
in response to activity of other genes during 1st
three weeks of adulthood , but can also be
turned on in response to conditions in the hive.
Development of Behavior

If colonies are artificially made up of only young
workers some become foragers much sooner
and others remain as nurse bees much longer.

It may be social encounters that stimulate these
changes.

Lack of encounters with older foragers appears
to hasten nurse bees transition to forager role.
Development of Behavior
 Adding
numbers of older bees to hives
that contain only young bees reduces the
number of young bees that become
foragers.

In contrast, adding more young bees does
not slow rate at which young bees become
foragers.
Development of Behavior
 Inhibiting
agent believed to be a chemical
called ethyl oleate that foragers
manufacture and store in their crop.
 When
foragers transfer food to nurse bees
they transfer the chemical, which slows
the nurses transition to foragers.
Development of Behavior
 In
honeybees, therefore, sequence of
behavioral changes is determined by
continuous interactions between genes
and both chemical and social
environments.
Nature vs Nurture Debate
 Nature:
genetic contribution to behavior.
 Nurture:
environmental contribution to
molding behavior.
 There
is a false dichotomy in popular
discussions in which traits are considered
to be genetically or environmentally
determined.
Nature vs Nurture Debate
 In
reality, all traits are the product of
gene-environment interactions.
 As
we saw in the process of song learning
there is considerable gene-environment
interaction.
Nature vs Nurture Debate
 Environmental
or genetic differences
among individuals can lead to differences
in development and finally differences in
behavior.
What causes individuals to develop
differently?

Environmental differences and behavioral
differences.

Many behavioral differences result from
differences in experience.

For example, marsh tits fed whole sunflower
seeds, which they can hide and later retrieve,
develop a larger hippocampus in their brain than
birds fed only powdered sunflower seeds.
Practice of storing and retrieving seeds alters
brain development.
Learning of nestmates in Polistes
wasps
 Polistes
wasps learn to identify the smell
of their natal nest and tolerate individuals
that smell like the nest (whether or not
they are relatives).
 Individuals
with a different smell are
attacked. Differences in how wasps
behave towards each other thus are based
on the smells they learned when young.
 Similar
discrimination between individuals
reared together versus apart has been
shown in Belding’s Ground Squirrels.
 Non-relatives
reared together act nicely
towards each other. However, relatives
reared apart also act nicely towards each
other.

Ground squirrels apparently learn what they
themselves smell like and use this information to
evaluate their relatedness to other individuals.

Trials in which squirrels provided with cubes
smeared with dorsal gland secretions of other
individuals respond more strongly to those of
non-relatives and discriminate between different
degrees of relatedness.
Genetic differences and
behavioral differences
 Breeding
experiments can show whether
behavioral differences between
populations have a genetic basis.
Funnel Web Spiders
 Spiders
in different habitats differ in their
speed of reaction to food being caught in
their webs.
 Streamside spiders react slowly.
 Desert grassland spiders react quickly.
 Is difference largely environmental or
genetic?
Funnel Web Spiders
 Spiders
bred in lab.
 Offspring of both populations kept equally
well fed. Then offered food.
 Desert spider reaction time: 3s.
 Streamside spider reaction time: 60s.
 Most of the difference in behavior
apparently due to genetic differences
between populations.
Migratory behavior of European Blackcaps
Migratory behavior of European
Blackcaps
 Blackcaps
are small European warblers,
most of which migrate to Africa to winter.
However, some spend the winter in Britain.
 What
causes this difference in behavior?
Migratory behavior of European
Blackcaps
 Peter
Berthold caught wintering blackcaps
in Britain.
 He
then bred these birds in central
Germany in outdoor cages.
Migratory behavior of European
Blackcaps
 In
fall Berthold looked at migratory
direction selected by birds.
 Used
an Emlen funnel to record
orientation.
Emlen Funnel
Blackcaps oriented in a westerly direction.
Conclusion? British birds from where?
Migratory behavior of European
Blackcaps
 Based
on orientation birds not from
Scandinavia or northern Britain.
 Birds
probably from due east of Britain
Belgium or Germany.
Migratory behavior of European
Blackcaps
 Could
environmental influences be
responsible?
 Perhaps,
just being in Germany causes
westward orientation.
Migratory behavior of European
Blackcaps
 To
check birds from SW Germany were
bred in captivity.
 Migratory
orientation was checked.
SW German birds oriented southwest.
Migratory behavior of European
Blackcaps
 Differences
in orientation between
populations largely determined by genetic
differences.
 Southwest
German birds migrate SW
traveling west of the Mediterranean via
Spain.
Migratory behavior of European
Blackcaps
 Andreas
Helbig has shown that Blackcaps
from Austria orient southeast.
 They
travel east of the Mediterranean via
Turkey and Israel.
Migratory behavior of European
Blackcaps
 Helbig
crossed birds from Austria with
birds from southwest Germany.
 What
direction did they orient?
Mean orientation of offspring south.
Inner ring
Adults.
Outer ring
Offspring.
Migratory behavior of European
Blackcaps
 Due
south is a poor choice. Requires bird
to cross the Alps and the make a long sea
crossing over the Mediterranean.
Single gene effects on
development
 In
theory a single gene difference could be
responsible for difference in orientation on
different Blackcap populations.
 Note
a single gene does not encode
migratory choices, but a change in a single
gene can result in many gene-environment
effects and ultimately produce a large
behavioral difference.
Two strains of Drosophila differ in
larval foraging behavior.
Rovers move a lot when feeding.
Sitters move very little.
Rover
Sitter
Rover/sitter behavior in
Drosophila
 When
the two strains were crossed in the
F1 generation all of the larvae were
rovers.
 A cross
of members of the F1 generation
produced a 3:1 ratio of rovers to sitters.
Rover/sitter behavior in
Drosophila
 One
gene appears to be responsible for
difference between phenotypes.
 The
rover allele is dominant and the sitter
allele is recessive. Gene that affects
rover/sitter behavior affects the olfactory
system and may affect fly’s ability to sense
its environment.
Rover/sitter behavior in
Drosophila
 Many
other single gene effects in
Drosophila.
Stuck: males don’t dismount after
normal 20 minutes of copulation.
 E.g.
 Coitus
interruptus: male copulates for only
10 minutes.
Single gene examples from lab
mice
 Mice
homozygous for allele for
defective form of  calmodulin kinase
have poor learning ability.
Single gene examples from lab
mice
 Mouse
placed in water-filled container.
 Submerged platform available for rest.
 Normal and mutant mice tested with
platform in random locations and original
testing position.
 Time to find platform measured.
When platform kept in same location as in training trials
wild-type mice found platform much faster than mutant mice,
but not if position of platform was randomized.
fosB gene
 In
normal mice sniffing and touching pups
causes changes in female’s brain that
prompt her to care for pups.
 Mice homozygous for inactive fosB gene
ignore their pups.
 Funtional fosB gene usually activated in
hypothalamus by smell of newborn pups.
Female with active fosB
Female with inactive fosB
Pups
Oxt gene
Mice missing Oxt gene cannot
produce oxytocin.
 Mutant male mice cannot remember
scent of females they recently
interacted with.

A gene “for”
 Remember
that one gene does not code
for a behavior.
 One
 Bit
gene codes for one enzyme.
a change in one enzyme can alter
numerous gene-environment interactions
and produce a detectable difference in the
phenotype.
A gene “for”
 The
phrase “a gene for” some behavior is
shorthand for: a change in the gene leads
to a change in behavior.
 All
else being equal, a change in a gene
can result in a detectable change in a
phenotype.
Evolution and behavioral
development
Garter Snake
In California, coastal and inland
populations of garter snakes differ in
diet.
Coastal garter snakes feed on banana slugs.
Inland populations eat other foods e.g. fish
and frogs.
 Is
there a genetic basis to the behavioral
differences in diet preference?
Steve Arnold studied populations to see if
there were genetic differences between
them.
Brought pregnant females into lab and
reared babies in isolation.
Offered slug pieces to snakes.
Inland snakes usually ignored slugs, coastal
snakes usually ate it.
Then tested newborn snakes on response to
odors.
Offered snakes flavored cotton swabs,
counted number of tongue flicks made.
Coastal individuals responded much more
strongly to slug odor.
Arnold carried out heritability studies.
Found little variation within either population.
Preference for slugs within a population
largely fixed.
Crosses between populations produced
individuals with wide variation in response
to slugs.
Suggests differences between populations
have strong genetic component.
What is evolutionary basis for difference
Advantage
to slug eating on coast is
between populations?
obvious.
Rare gene for eating slugs would spread
rapidly.
Artificial selection and
behavioral evolution
 Nest
building in mice.
 In
starting population mice used 13-18
grams of cotton to line their nests.
 Carol
Lynch selected for “high”, “low” and
“control” groups of mice.
 After
15 generations amounts of cotton
used by mice were:



Controls 15g same as original population.
High 40g
Low 5g
Other examples of Artificial
Selection
 William
Cade has selectively bred crickets
to sing rarely or almost continuously.
 In
only two generations of artificial
selection Pulido et al. showed that the
timing of migration in European Blackcaps
could be delayed more than a week.
Artificial Selection
 Artificial
selection experiments show that
(i) behavior is subject to selection and (ii)
populations contain sufficient genetic
variability to evolve rapidly.
Adaptability of behavioral
development
 As
we have seen the development of
behavior such as singing can be strongly
influenced by environmental effects.
 It is important for development of behavior
to be resilient to disturbance so that
normal behavior can develop as often as
possible.
 Process of developmental homeostasis
reduces effects of disturbance.
Adaptability of behavioral
development
 Harlow’s
“experiments” with Rhesus
monkeys showed that rhesus monkeys
entirely derived of contact with mothers
and “reared” by artificial surrogates gained
weight and grew normally but behaviorally
developed abnormally (BIG surprise!) and
were terrified of other monkeys if exposed
to them.
Adaptability of behavioral
development
 However,
monkeys given even 15 minutes
contact a day with other young monkeys
developed essentially normally.
Adaptability of behavioral
development
 As
adults, these monkeys interacted
normally with others unlike those
individuals which had no social contacts
as infants, which were withdrawn or very
aggressive.
Read Dawkins chapters 4 and 5 for next
Friday.
First exam is Wednesday February 22nd.
Developmental homeostasis in
human embryonic development
 We
saw in studies of songbirds that adult
ability to learn and sing complex songs
was affected by food deprivation during
period of rapid nestling growth.
 In
humans food deprivation of the mother
during pregnancy appears not to have
major effects on the fetus’ intelligence.
Developmental homeostasis in
human embryonic development
 Studies
of children whose mothers were
food deprived during the Nazi transport
embargo of Holland in late WWII showed
that these children had comparable
intelligence scores and rates of mental
retardation as children whose mothers
were not food deprived.
Symmetry and attractiveness
 Many
organisms are influenced by how
symmetrical other individuals are when
making mate choices.
 Asymmetries
are believed to be caused by
problems in development and symmetry
thus signals an ability to overcome
developmental challenges.
Symmetry and attractiveness
 There
is some evidence that humans
include symmetry in their ratings of an
individuals’ attractiveness, but data are not
conclusive and there is considerable
debate.
 Female
brush-legged wolf spiders,
however, are significantly more likely to
mate with males whose foreleg hair tufts
are symmetrical than those who are not.
 Study
was carried out using video images
of spiders that were identical apart from
the digitally manipulated foreleg tufts.
Polyphenism
 In
many species multiple alternative
phenotypes occur in the same species (i.e.
distinctly different body types occur).
 These
different phenotypes arise as a
result of environmental effects. The
environmental influence sends the
developing organism down one or another
distinct developmental pathway.
Developmental flexibility in Tiger
Salamnders

Larvae live in ephemeral ponds.
 Most
follow “normal” development and eat
small invertebrates.
But some become cannibals (bigger with
larger teeth) and eat smaller salamanders.
Normal form
Cannibal
What factors affect decision to
become a cannibal?
 Ideas?
What factors affect decision to
become a cannibal?
 Relatedness
of cannibal to others in pool.
 Density of salamanders
 Size distribution of salamanders
 A salamander
surrounded by lots of nonkin can benefit by becoming a cannibal.
 By
growing faster it can escape from the
pond sooner.
 Developmental
flexibility allows
salamander to adjust its development if
conditions are suitable, but not otherwise.
Behavioral flexibility

Many animals choose among different
behavioral phenotypes depending on
environmental circumstances.

For example, in many fish males adopt different
roles depending on their size and status. Large
males defend territories but smaller satellite
males act as sneakers darting in and releasing
sperm whenever the dominant male mates with
a female.
Behavioral flexibility in
Haplochromis burtoni
 In
cichlid fish Haplochromis burtoni
territorial males are brightly colored and
satellite males are dull.
 Behavior
is related to brain structure.
Satellite
male
Territorial
male
Behavioral flexibility in
Haplochromis burtoni
 GnRH
(gonadotropin releasing hormone)
neurons in hypothalamus are 6-8 times
larger in territorial males than in satellites.
 GnRH
neurons stimulate testes
development and aggressive behavior.
Behavioral flexibility in
Haplochromis burtoni
 Interestingly,
GnRH size is variable.
 If
male loses territory his neurons shrink
and he becomes dull colored.
 If
territory opens up, male enlarges
neurons, switches to aggressive territorial
mode
Behavioral flexibility in
Haplochromis burtoni
 Unpredictable
social environment favors
flexibility in Haplochromis.
 Neuronal
flexibility allows males to adopt
best strategy for conditions.
Learning

Learning major element in behavioral
flexibility. Ability to make use of
experience in adjusting behavior can
be selectively very advantageous.
Learning in Australian Thynnine
wasps
 Males
search for females based on
pheromones they produce.
 Orchids
attract males using a similar
scent.
 Orchid
mimics female wasps appearance
too. When male lands and attempts to
mate he gets a surprise.
Male tries to mate with “female wasp”
on orchid, instead acquires a pollen sac.
Female wasp
Fake wasp
Pollinia on
wasp’s back
Wasps don’t learn to avoid orchids in
general.
But, do learn to avoid orchids they have
visited before.
Learning in Australian Thynnine
wasps
 What
do wasps learn?
 Orchid’s
location or orchid’s scent?
 Speculation:
If wasps could learn scent
differences how plants benefit from having
wasps revisit them?
Costs and benefits of learning
 For
learning and flexible behavior to
spread by natural selection, benefits must
exceed costs.
 Benefits
are the ability to exploit the
environment more effectively.
 What
are the costs?
Costs and benefits of learning
 Costs:
Major cost is additional energy
required to make/maintain neuronal
tissue.
Example of cost:
West coast marsh wrens sing more songs
(100) than east coast marsh wrens (40).
Song system in brain weighs 25% more
in west coast birds.
Costs of large brain in humans
 In
humans: Brain 2% of body weight.
 But
requires 15% of body’s oxygen and
20% of energy.
 Other
costs to large brains in humans?
Costs of large brain in humans
 Difficulty
in giving birth.
Behavioral flexibility expensive.
Should only evolve when benefit
outweighs cost.
Clark’s Nutcracker seed-storing specialist.
Much better at remembering where
Something is located than other crows.
Not better at remembering colors, a nonspatial task. Memory skills determined
by bird’s needs.
Intraspecific variability in
learning
 Behavioral
flexibility does not only differ
between species.
 In
species where males and females
experience different selection pressures,
differences in learning ability occur.
Spatial learning in voles
 Male
meadow voles are polygynous.
Their home ranges are 4X larger than
those of females.
 Prairie
voles are monogamous. Males
and females have same size home ranges
Spatial learning in voles
 Spatial
learning abilities of voles was
tested in mazes.
 Male
meadow voles made significantly
fewer mistakes than female meadow
voles, but there was no difference
between the sexes in the performance of
male and female prairie voles.
Spatial learning in voles
 Male
meadow voles have a large
hippocampus than females and this area
in the brain processes spatial information.
 However,
the enlarged hippocampus only
develops during the breeding season.
Spatial learning in cowbirds
 Female
cowbirds parasitize other birds
nests. They need to be able to remember
nest locations and monitor them over time.
Female cowbirds have a larger
hippocampus than males. No difference
between sexes in related, but nonparasitic grackles and red-winged
blackbirds.
Operant conditioning
 Spatial
learning not only behavior that has
clearly been shaped by selection.
 In
operant conditioning (or trial and error
learning) an animal learns to associate an
action with its consequences.
 E.g.
a rat pushes a lever and gets a food
pellet.
Operant conditioning
 Usually
a behavior and its consequences
must be closely linked in time for
conditioning to occur.
 However,
in rats tasting novel foods
nausea that occurs several hours after
eating a food will be associated with that
food, which in future will be avoided.
Another example of operant conditioning is
that predators learn to recognize noxious
prey after tasting them.
How does warning
coloration benefit
animal that is tasted
if it is killed?
Does operant conditioning occur in
humans?