lecture 29 - introduction to animal behaviour Flashcards
What is Tinbergen’s “four questions” approach (1963)?
The question “Why does that behaviour occur?” is actually four questions.
Causation (Mechanism)
How does the body operate as a machine in order to make that behaviour?
2. Development (Ontogeny)
How has the animal developed so as to produce that behaviour?
Adaptive Function:
What is the survival/reproductive/fitness value of that behaviour?
Evolutionary History (Phylogeny)
What are the evolutionary changes that led to that behaviour?
A complete understanding of behaviour requires all four.
This is the basis of modern ethology
The four questions approach is often useful for answering other “why” questions
Using Tinbergen’s Questions - Why does a bird sing?
Causation: Hormones? Apparatus?
A bird sings because its hormone levels have changed in response to changes in day length. Or, more immediately, a bird sings because air passing through its specialized singing organ, the syrinx, causes membranes to vibrate rhythmically.
Development: Genes? Environment?
In birds, typically it’s the male that sings, and he has learned the song from his father.
Adaptive function: Mate attraction?
it could be that a male bird sings in order to attract a mate and then reproduce.
Evolutionary history: Related species?
Complex bird songs may have evolved from vocalizations made by ancestors that were reinforced and became increasingly stereotyped or ritualized over time, so much so that we can often identify a bird species simply by hearing it sing. A behavior may have originated to fulfill a function different from the one it currently serves. For example, the song of a particular species may have first evolved to claim a territory but now is used to attract mates.
Give examples of innate behaviour
The answers to Tinbergen’s questions rely on an interplay between genes and the environment. The influence of genes is especially clear in innate behaviors, those that are instinctive and carried out regardless of earlier experience.
Here, a male silkworm moth of the genus Bombyx flies upwind toward the source of a female-produced pheromone, an airborne chemical signal that communicates with members of the same species, in this case to attract the opposite sex. Pheromones released from a female’s abdominal gland are sensed by small hairs on the male’s antennae. In the presence of pheromones, the antennal sensory hairs fire action potentials. When about 200 hairs are activated per second, a male flies upwind distances of a kilometer or more, tracking the increasing pheromone concentration until he finds the female. The male does not need to learn this behavior; he performs it spontaneously. His genes encode molecular receptors to which the pheromone binds, and this binding triggers a cascade of events that result in the moth heading up the pheromone’s concentration gradient.
A particular behavior may also depend on an individual’s experience. In this case, the behavior has been learned. Even neurologically simple organisms have a considerable capacity to learn.
What is a FAP?
Displays are an example of a fixed action pattern (FAP). A FAP is a sequence of behaviors that, once triggered, is followed through to completion. A classic example, originally studied by Tinbergen, is the response of a goose to an egg that has fallen from its nest.
The stimulus that initiates the behavior is the key stimulus and, in this case, it is the sight of the misplaced egg. This sight provokes in the goose an egg-retrieval FAP, which consists of rolling the egg back to the nest with the underside of its beak (a). This response cannot be broken down into smaller subunits and it is always carried out to the end, even if it is interrupted.
In fact, the goose will persist in its efforts even if the researcher ties a string around the misplaced egg and removes it while the goose is in mid-action. The goose will still continue the task of rolling the now-absent egg (b). It is possible to understand this behavior by varying attributes of the key stimulus (in this case, the misplaced egg). The researcher can make models that vary in only one attribute to investigate how sensitive the goose is to aspects such as color or shape. A remarkable finding is that many birds respond most strongly to the largest round object provided, even a soccer ball, as illustrated in Fig. 45.3c.
A soccer ball in fact not only elicits the egg-retrieval FAP, but it does so even more strongly than does a normal egg. The soccer ball is considered a supernormal stimulus because it is larger than any egg the goose would naturally encounter and elicits an exaggerated response.
What is feature detection?
The nervous system must process stimuli in order for a response to be carried out. We know that stimulus recognition is often carried out by feature detectors, specialized sensory receptors or groups of sensory receptors that respond to important signals in the environment. Frogs provide a good example of this when distinguishing their species-specific call.
To study this, recordings of frog calls can be altered and played back in order to monitor the responses of frogs. By altering different components – pitch, duration, and pulse frequency, a frog’s auditory nerves act as a feature detector. The combination of different feature detectors stimulated by different components adds up to the recognition by the frog of a specific call. Once the sound has been correctly identified, the appropriate behavior follows.
Describe feature detection with toad prey capture
Faced with a moving prey item toads will: Turn to face it Approach and stare at the prey Strike at it (with tongue) Swallow Wipe its mouth
Toads react differently to different shapes and sizes of objects
Worms are favoured, anti-worms not favoured, and medium sized squares work well.
The retinal image maps directly to regions in the optic tectum
TH3 cells are active when anti-worms are present – they inhibit T5(2) cells
T5(1) cells are active when worms are present – they activate T5(2) cells
T5(2) cells activate prey capture behaviour
Describe the hormonal influence on behaviour
The complexity of hormones on behavior can be demonstrated in the Anolis lizards. Females of Anolis carolinensis collected in the spring and housed in the laboratory under a spring light-dark cycle prepare for reproduction, and about 80% of individuals have active egg follicles in their ovaries (a).
If one male is added to a group of females, however, that figure increases to 100% (b). The courting behavior of the male lizard stimulates the females to produce hormones that cause the full development of the ovaries, making the females reproductively active.
If a group of males instead of a single male is added to an all-female population, on the other hand, only about 40% of the females undergo ovarian development (c). This unexpected result seems to occur because the males interact and fight among themselves rather than court the females, and therefore the courtship stimulus is lacking.
Castrated males (which do not produce testosterone) that are added to a group of females have no effect on rates of ovarian development, which remains about 80% (d). They fail to court because the behavior is testosterone-mediated. However, a castrated male that is injected with testosterone does display courting behavior and has the same effect as the presence of a single male, inducing all the females to undergo ovarian development (e).
Give an example of long term behavioural sequences - Barbary dove hormones: Lehrman
- Winter: males aggressive
- Spring: males court females
- Both sexes nest-build
- Female lays and incubates
- Female feeds chicks crop milk
The hormone cascade:
Low testosterone in male, aggression -> Hormones in
female hold back reproduction
Spring - longer day length gives testosterone and
male courting -> Female produces gonadotropin -> Ovary growth -> Ovaries release oestrogen -> Female nest building -> Male nest building, prolactin in female -> Crop milk
How are genes and behaviour related?
Artificial selection, in which humans breed animals and plants for particular traits, provides strong evidence of the role of genetics in influencing behavior. Dogs were domesticated from wolves about 10,000 years ago. Today, there is great diversity among dogs, although they are all the same species. Obviously, there has been extensive selection on physical traits, with the result that a Dachshund, for example, looks quite different from a German Shepherd or Great Dane. Selection has also been applied to behavior: A Pointer has extraordinary “pointing” behavior that specifies the location of a hunter’s prey, and a Border Collie is an excellent herder
Describe how molecular techniques are used to test the roles of genes in behavior
Molecular biology is changing the way we approach behavioral genetics. Some studies have identified complex behaviors that are strongly influenced by a single gene. In Drosophila, there are two different alleles of the foraging (for) gene—fors and forR—that are common in populations. These two alleles have different effects on the behavior of Drosophila larvae. In the absence of food, both “sitter” (fors) and “rover” (forR) larvae move about in search of food. In the presence of food, however, sitters barely move, feeding on the patch on which they find themselves, whereas rovers move extensively both within a patch of food and between patches (a).
Both forms are present in natural populations (b); typically, 70% are rovers, 30% are sitters. This proportion suggests that both strategies are adaptive. Furthermore, studies have shown that rovers are selected for in crowded environments in which there is an advantage to seeking new food sources, and sitters are selected for in less-crowded ones because they take maximum advantage of their current food source. In this case, variation at a single gene affects a complex behavior in fruit flies.
Describe how a study on fruit flies was used to look at whether behaviours are heritable
The genes that control behaviour in fruit flies play
similar roles in other animals. The gene has been named “for”. It codes a cGMP-dependent protein kinase, that affects brain activity. The foraging gene is present in other insects as well, including honeybees, suggesting that it has been evolutionary conserved. Honeybees with low levels of for expression in their brain tend to stay in the hive (nurses), whereas those with high levels of for expression are likely to be foragers. To determine this, levels of for mRNA were measured in honeybee nurses and foragers. The results showed that levels of for mRNA are significantly higher in foragers than in nurses (a). However, foragers are older than nurses, so it was unclear whether the increased expression in foragers compared to nurses is associated with differences in age or differences in behavior. Therefore, the experiment was repeated with honeybees that forage at a young age. These young foragers also have higher for mRNA levels than do nurses (b).
The for gene encodes a cGMP-dependent kinase that phosphorylates other proteins. Honeybee nurses were treated with cGMP to activate the kinase and their subsequent behavior was monitored. A related compound, cAMP, with a chemical structure similar to cGMP but which does not affect the kinase, was used as a control, to ensure that any effect observed was specific for the pathway and not the result of the treatment.
Treatment with cGMP changed the behavior of nurses, causing them to forage. Furthermore, cGMP acted in a dose-dependent fashion: The higher the dose, the more foraging behavior was observed. No effect on foraging was seen in the control treatment.
The same gene that is involved in two different behavioral phenotypes in fruit flies (sitters vs. rovers) is also involved in a developmental behavioral change in honeybees (nurses vs. foragers). This finding suggests that a gene can have related but different functions in different organisms.
