Chapter 8 - Development of behavior Flashcards
Influences on Behavioral Development
- Development of the Nervous System
- Hormonal Environment
- Characteristics of the Environment
- Experience Through Play
Development of the Nervous System
Behavior is controlled primarily by the
nervous system, so it is intricately linked
during development.
* The development of key parts of the
nervous system underlie the appearance
of new behaviors.
Sometimes, the
underlying neural
circuitry disappears
when a behavior
disappears.
* Example: Tobacco
Hornworm (Manduca
sexta)
* The loss of neural
circuitry does not
always happen.
Physical Characteristics of the Environment
Leopard Gecko (Eublepharis macularius)
* Exhibit temperature-dependent sex determination.
* Incubation temperature also affects aggressive and
sexual behaviors in adults.
Experience through Play
Play is important in the development of many
mammals, some birds, and even some
reptiles.
* Play can be difficult to define, even though
we seem to know what it is when we see it.
* Not usually characterized by any specific
behaviors or series of behaviors. Play
borrows pieces of other behavior patters and
often combines them.
Several Types of Play
- Social Play
- Locomotor Play
- Object Play
Why do animals Play?
- Physical: Training for strength, endurance, and
muscular coordination, especially as they relate
to fighting and prey capture. - Social: Practice of social skills such as
grooming, sexual behavior, establishment of
social bonds, communication, etc. - Cognitive: Learning specific skills improving
overall perceptual abilities.
sensitive Periods
Initially called critical periods, defined by Lorenz (1935) as a
phase of susceptibility that was brief, well-defined, and within
which exposure to certain stimuli produced irreversible effects on
subsequent behavior.
* Now referred to as sensitive periods, the definition has been
defined over time. We now know that these periods a) can be
fairly extended, b) are not sharply defined but gradual in their
onset and termination, c) differ in duration among species and
even individuals, and d) depend on the nature and intensity of
stimuli both before and during the sensitive period. Also, we
know that most behaviors based on sensitive periods are not
irreversible.
* So, a modern definition of a sensitive period is a time during
development when certain experiences have a greater influence
on the characteristics of an individual than at other stages
Sensitive Periods – Filial Imprinting
Young ducklings tend to follow their mothers.
* Greylag Goose (Anser answer) – Clutch was divided into
two groups. Those hatched by mother imprinted on her.
Those hatched in an incubator imprinted on the first
moving object.
* There are two distinct processes involved in the process
of attachment to a parent. First, there is a predisposition
to approach objects with the general characteristics of
conspecifics. Second, the young bird learns, through
exposure to its mother, her particular characteristics and
then preferentially follows her. These two processes
appear to be localized in two different areas of the brain.
In Mallards (Anas platyrhynchos), ducklings raised in an
incubator were exposed to a stuffed replica of a Mallard
that emitted calls of Mallards, Wood Ducks, or Chickens.
For a fourth test group the replica was silent. The
ducklings showed a preference for the calls of Mallards
over the calls of the other species. No ducklings showed
an interest in the silent replica.
* This shows that a) auditory cues are important in filial
imprinting, and b) the ducklings preferred the maternal
call of their species, even though they had not heard it
before.
* This preference by the ducklings to the call of their own
species is an example of the predisposition mentioned
on the previous slide.
* If ducklings are raised in isolation AND are
inhibited from calling prior to hatching
(muted), then they will not show a
preference for the calls of their species.
* Therefore, auditory experiences prior to
hatching (either hearing their nestmates or
themselves) are important because they
induce a predisposition for the calls of
Mallards.
What about the role of sensitive periods?
* Muted ducklings that were exposed to
contentment calls (calls from other chicks)
approximately 24 hours prior to hatching
showed a preference for Mallard calls;
those that were exposed to contentment
calls approximately 24 hours after
hatching did not show a preference for
those calls.
Development of Bird Song
Researchers have identified multiple song
nuclei. These nuclei are linked by two major
pathways.
– The posterior pathway is involved in the production of
song.
– The anterior pathway is involved in the acquisition of
song.
* Other areas are involved in the perception of
song (hearing) and the storage of song
memories.
Zebra Finch (Taeniopygia guttata)
Zebra finches are a social species native to
Australia.
* Only males sing (mostly for mate attraction).
In Zebra Finches, the song nuclei are larger in males than in
females; they also contain more neurons and larger neurons.
* How do these sex differences arise?
* Genetics: The differential action of genes encoded on the sex
chromosomes likely prompts sexual differentiation of the song
system.
* Hormones: Estrogen appears to masculinize the brain (see
next slide). One hypothesis for sexual differentiation of the
brain is that the genes on sex chromosomes cause
differences in the synthesis of estrogen in the brain, and that
higher levels of estrogen in male brain tissue masculinize the
song system.
* There is a sensitive period, around the time of hatching, when
the brain is particularly sensitive to the effects of estrogen.
Hormones have both organization and activational
effects on singing behavior. Even though the brain
is masculinized during development
(organization), elevated levels of testosterone in
adulthood are necessary for song production
(activation).
* Females that receive estrogen implants after
hatching and therefore develop enlarged song
nuclei (previous slide) do not sing in adulthood
unless given testosterone. Females who do not
receive estrogen implants after hatching do not
sing when given testosterone in adulthood.
For many species, the hormonal activation
of song occurs on a seasonal basis.
* During the breeding season, the volumes
of song nuclei may increase by 200%.
* The song system regresses during the
non-breeding season, and song
production diminishes or ceases.
What role does learning play in the development of bird
song?
* Under natural conditions young male White-crowned
Sparrows hear the songs of their father and other adult
males during the first summer and autumn of life.
* During these first few months of life, young males
produce only subsong, which is a highly variable,
rambling series of notes that is not similar to adult song.
* As the first breeding season approaches, the song starts
to resemble a full adult song. This is called plastic song.
* The song becomes fully developed at the start of the
breeding season
White-crowned Sparrow (Zonotrichia leucophrys)
Isolated White-crowned Sparrows will
develop normal song if they hear tapes of
adult song, but only if that exposure
occurs between 10 and 50 post-hatching.
Thus, there is a sensitive period for song
learning.
Young White-crowned Sparrows reared in
isolation develop abnormal song.
* In addition, young sparrows must also be
able to hear themselves sing. Young
males exposed to song during the
sensitive period but then deafened before
the onset of subsong produce a rambling,
variable song as adults.
song
development in sparrows consists of two phases
The Sensory Phase
The Sensorimotor Phase
The Sensory Phase
This phase includes the
acquisition of song knowledge and the storage of that
song information in memory. During this time, the bird
produces only subsong, which does not involve retrieval
or rehearsal of learned material
The Sensorimotor Phase
This phase involves the
retrieval of learned song from memory and the
rehearsing of that song. The song improves over time
until it matches what was initially stored in memory. The
final adult song remains virtually unchanged for the rest
of the sparrow’s life.
What about sensitive periods in song learning?
The length and timing of sensitive periods can
vary greatly. Canaries are an example of lifelong
learners (or open-ended learners) because they
can continuously alter their songs throughout
adulthood. Birds like Zebra Finches and White-
crowned Sparrows are age-limited learners
(close-ended learners) because they have a
restricted period of learning early in life.
Variation in the length and timing of sensitive periods
likely reflects differences in life histories of species.
* The Brown-headed Cowbird (Molothrus ater) is a brood
parasite. Therefore, if young males learned their songs
from other males in the area, they would likely end up
singing the songs of their hosts. But this does not
happen. As adults, they sing the cowbird song.
* So, when is the sensitive period for this species?
* They do join flocks of other cowbirds aftert they leave the
nest, but most birds are not singing at that time. It turns
out they do not perfect their song until their second
winter. This gives them an entire extra year to listen to
the songs of adult males.
