lecture 30 - learning, navigation and rhythms Flashcards
What are some different forms of learning?
Learning - changes in behaviour due to experience
Non-Associative – without specific outcome (reward/punishment)
Sensitization – sea slug gill withdrawal
Habituation – chick crouching
Associative (conditioning) – link two events
Classical (stimulus/behavior)
Operant (behavior/response)
Non-associative learning is learning that occurs in the absence of any particular outcome, such as a reward or punishment. One type of non-associative learning is habituation, which is the reduction or elimination of a behavioral response to a repeatedly presented stimulus. Chicks presented with silhouettes flying overhead provide an example. Initially, any overhead silhouette provokes a defensive, crouching posture, but eventually, chicks habituate to overhead silhouettes that have proved not to be threatening. In the absence of any consequences, chicks no longer crouch in response to a harmless silhouette passing repeatedly overhead.
Sensitization is another form of non-associative learning. Sensitization is the enhancement of a response to a stimulus that is achieved by presenting a strong or novel stimulus first. This pre-stimulus makes the animal more alert and responsive to the next stimulus.
Associative learning (also called conditioning) occurs when an animal learns to link (or associate) two events. Perhaps the most famous example of conditioning is Ivan Pavlov’s dogs. Pavlov first presented the dogs with meat powder, and they salivated in response. He then presented the dogs with an additional cue, a ringing bell, whenever he presented the dogs with meat powder. Salivating dogs did so at the sound of the bell alone, in expectation of the meat reward. This form of conditioning, in which two stimuli are paired, is called classical conditioning. In this case, a stimulus that leads to a behavior (the smell of the meat powder) was paired with a neutral stimulus (the bell) that initially had nothing to do with salivation. On the other hand, if the behavior is punished (negatively reinforced), the response becomes less likely. This form of associative learning is called operant conditioning.
What is classical conditioning?
e.g. Pavlov's dogs Unconditioned stimulus – food Unconditioned response – salivate Conditioned stimulus – e.g. light Conditioned response – salivate
In classical conditioning, the
stimulus changes
What is operant conditioning?
Unconditioned stimulus – lever
Unconditioned response – ignore lever
Conditioned stimulus – lever
Conditioned response – push lever
In operant conditioning the
response changes
What is imprinting?
In addition to adaptive predispositions for what can be learned and not learned, many species exhibit predispositions for when learning takes place. This is particularly evident in imprinting, a form of learning typically seen in young animals in which they acquire a certain behavior in response to key experiences during a critical period of development.
Konrad Lorenz made imprinting famous by exploiting the observation that newly hatched goslings and ducklings rapidly learn to treat any animal they happen to see shortly after hatching as their mother. Lorenz found that, if he was the first person the hatchlings saw, they would follow him as though he were their mother. This behavior is adaptive because the first being that a hatchling normally sees is a parent. This type of imprinting is called filial imprinting, and it is most common in species whose offspring leave the nest and walk around while still young.
Experiments have shown that filial imprinting typically occurs during a specific, sensitive period in the animal’s life and that the results are usually irreversible. After Lorenz’s baby ducks had imprinted on him, they would not change their minds about who their parent was even when presented with their real mother duck.
How do changes in orientation take place?
The ways in which animal nervous and endocrine systems and the input of experience are integrated to generate adaptive behaviors are remarkable. Some of these adaptive behaviors include ways of moving, navigating, and keeping time.
Even the simplest bacteria and protozoa are capable of moving in response to stimuli. A Paramecium that finds itself in an unfavorable environment, such as water that is too warm or too salty, increases its speed and begins to make random turns. When it finds favorable conditions, such as cooler water, it slows and reduces its turning rate. These random, undirected movements are termed kineses.
In contrast, taxes (singular, taxis) are movements in a specific direction in response to a stimulus. An interesting example of a taxis is movement oriented to a magnetic field, a behavior called magnetotaxis—the term was first used by the American microbiologist Richard Blakemore in 1975. Blakemore had found that anaerobic bacteria in the genus Aquaspirillum, which swim by means of flagella, tend to swim toward magnetic north. These bacteria can be attracted to the side of a dish with a bar magnet. Little bits of magnetized iron oxide, arranged in a row inside the bacterial cell, allow the bacteria to sense the magnetic field. Blakemore hypothesized that the bacteria swim north in order to swim deeper. In the northern hemisphere, the north magnetic pole is inclined downward. At Woods Hole, Massachusetts, where these bacteria were found, the magnetic pole is at about a 70-degree incline. Since the bacteria are anaerobic, they must stay buried in sediment, and they remain buried by moving downward along the magnetic gradient.
To test his hypothesis, Blakemore looked for and found bacteria in New Zealand that exhibited similar behavior to the Woods Hole bacteria except that they swam toward the south magnetic pole, bringing them downward in the southern hemisphere. Finally, he took New Zealand cultures back to Woods Hole, where the bacteria swam up into the oxygen and died. These experiments demonstrated that bacteria are able to sense a magnetic field and move in a directed fashion relative to that field.
Describe innate navigation
Turtle phototaxis : changing to red lights around turtle nest beaches helps hatchlings reach the sea Desert ants (Cataglyphis): The ants forage on their own by moving in a series of short straight lines with periodic changes of direction until they find food. Then they go straight home. The ants use a pedometer to estimate distance travelled
Describe the use of landmarks - Tinbergen’s digger wasps
Learning takes many forms. Much learning, including human learning, is based on imitation. The capacity to learn in many instances seems innate. Female digger wasps are foragers. Tinbergen showed that a digger wasp learns the landmarks around her nest and then uses this information to find her way back to it from hunting. In his experiment, Tinbergen placed a ring of pine cones around a wasp’s nest and, after she had flown out and returned a few times, moved the circle of pine cones to the side of the nest. The wasp flew past her own nest and went directly to the center of the ring.
This adaptive aspect of animal learning is also revealed by taste aversion experiments, in which an animal typically learns to avoid certain flavors associated with a negative outcome.
How are navigation and clocks used together?
The importance of the sun compass coupled with the biological clock in homing pigeons can be demonstrated by experimentally disturbing the birds’ clock.
If you are in the northern hemisphere and you know the time is 12 noon, then the sun is due south of you. Orienting yourself by this method is possible only if you know the time, so the question arises whether homing birds have the ability to tell the time. One way to answer this question is to “clockshift” the birds. Researchers raise birds in an artificial day– night cycle that is out of sync with the actual one. When released into a sunlit environment, these birds’ sense of time is shifted by a set number of hours (refer to table).
If a bird’s ability to home is dependent on an internal clock, clockshifting should affect the bird’s homing ability in a predictable way. Given that the sun travels 360 degrees in 24 hours, a 6-hour clockshift will result in a 90-degree error in homing direction because 360/(24/6) = 90.
In the experiment, birds were clockshifted by raising them in a chamber under an artificial light. Birds from a home loft in Ithaca, New York, were released on a sunny day at Marathon, New York, about 30 km east of Ithaca. Release on a sunny day made it possible for the birds to use the sun’s position to navigate.
The results were as expected for the control birds (those that were not clockshifted) as they were good at picking the direction of their home loft. The results for the clockshifted birds were very different: They miscalculated the appropriate direction. These birds headed approximately northward, as shown by the positions of the red triangles on the compass in the figure. To interpret these findings, assume the birds are released at 12 noon, when the sun is due south. The control birds know to fly in a direction 90 degrees clockwise from the direction of the sun, but the clockshifted birds “think” it is 6 p.m., so they expect the sun to be in the west. Their 90-degree clockwise correction, then, has them flying due north.
The clear difference between control and clockshifted birds in the experiment shows that an internal time based sun compass is an important component of the birds’ homing abilities. However, the scatter of points (for both experiment and control) suggests that other factors are also important.
What are different types of biological rhythms?
Circadian rhythms – day/night (trout) Circannual – breeding, migration, hyperphagia Ultradian – tidal swimming in shannys Infradian – Palolo worm Infraannual – Periodic cicada
How do mammalial circadian rhythms work?
Light/dark cycles -> Optic nerve -> Suprachiasmatic nuclei of hypothalamus (if this is destroyed rhythm lost)
-> Circadian activity of per and tim genes –Protein products–> Pineal gland produces melatonin
(drowsiness in diurnal animals)
