Principles of Early Ethology

Classical Theory

Fixed Action Pattern (FAP) This is an innate and stereotyped

coordination and patterning of several muscle movements which when released proceed to completion without requiring further sensory input.

Almost totally independent of feedback. = extreme case of prewired behavior performances which have come to be known as "motor programs". = consummatory behavior.

Ex. Greylag goose (Lorenze & Tinbergen) What does a goose do when it spots an egg outside

the nest? Goose fixates on egg, slowly rises, extends neck

over egg and rolls it back into the nest with bottom of bill. Adjusts as it rolls. Nestles down to incubate.

Seems to be sensible solution to a problem, but L. and T. were struck by the stereotypy of the pattern. Seemed machine-like. Was this a program which once triggered would run to completion?

Greylag goose Messed it up with an experiment Removed egg after neck extension begun. Animal

completed the behavioral sequence and settled down on the nonexistent egg.

T. found that a wide variety of only marginally egg-like objects trigger the behavior. e.g. beer cans and baseballs. Found. any large, nearby convex object with smooth rounded edges would trigger. Once in nest felt wrong to goose and were discarded. At this point a new set of stimul are responded to.

IRM, releasers, sign stimuli L & T. Geese must possess an innate and

highly schematic filter which, when stimulated by anything satisfying its crude criteria for "eggness", triggers (releases) the FAP.

Trigger - filter complex = innate releasing mechanism (IRM)

Features of stimulus essential to triggering it = sign stimuli. Ea. FAP can be released by >1 sign stimulus

IRM, releasers, sign stimuli Releaser. When the sign stimulus is a behavioral

act of a conspecific animal, such as an alarm signal or any other communicative behavior, it is technically termed a releaser. Often used synonymously with sign stimulus, but really subset.

Effects of sign stimuli can be additive so that releasers of egg rolling are; convexity, smooth rounded edges, nearness to nest, size. A round object near the nest may occasionally be a sign stimulus, but better if it is smooth and convex. Better still if large.

This additive effect is called the law of heterogenous summation.

IRM, releasers, sign stimuli When animal responds to one aspect of

stimulus object only = sign stimulus. In nature, simple, but diagnostic criteria of

IRM exclude almost everything the goose is likely to encounter which is not an egg.

Summary. Egg rolling is a behavioral unit Specific trigger satisfied by "eggness" (sign

stimulus) --> recovery of egg (FAP) IRM filters information as it is received.

When a stimulus satisfies innate criteria, the fixed action pattern is released and the egg is recovered.

Summary. The system is stimulated by a "drive" or

"motivation" = appetitive behavior. Eggs are rolled only from the onset of incubation until hatching is due to begin.

Orientation is often a component of appetitive behavior. Can be seen at the same time as the consummatory act. L&T separated it in goose by observing that goose will "retrieve" missing egg, but not make adjustments - side to side - which are necessary when a real egg is there.

Foreign objects recognized in the nest --> discarding behavior by a goose which has just taken great pains to retrieve. = separate program.

Famous Sign Stimulus Reported by Spalding (Bertrand Russel's

teacher) in 1873, rediscovered by L. and systematically investigated by T. = escape reaction of naive chicks when shown silhouette of flying hawk.

Tinbergen showed the chicks a model like that in the picture. When the model is moved in one direction it resembles a hawk while in the other direction it resembles a goose.

He found the birds displayed an alarm reaction to the hawk model but not the goose

Famous Sign Stimulus Adaptive value of response clear. Crucial for

young birds to "know" to hide from hawks right away. Such a simple stimulus, which triggers IRM, would be sufficient for even the most myopic chick.

Conclusion was that animals come neurally wired to recognize important stimuli in their environment on the basis of 1 or 2 simple, but diagnostic features which trigger appropriate behavioral responses. The most obvious of these are FAPs.

Criticisms Later studies showed that the situation was

not that simple. Learning is involved. There are many geese

where Tinbergen did his experiments and the geese became habituated to them.

The birds show a fear reaction to any stimulus flying over the nest at first, but become habituated to the geese. Hawks are rare so they continue to elicit the response.

 Supernormal Releasers

T. (L. would never) asked how un-egglike an object could be and trigger the egg-rolling releasing mechanism. Led to one of T's classic choice experiments. Allowed to choose between goose egg and volleyball these choose the volleyball. = Supernormal stimulus.

Supernormal Releaser Stickleback male fish will attack almost

anything that has a rounded red bottom even though the model scarcely resembles a rival fish. The model is a supernormal releaser.

http://www.biology.ucsc.edu/~barrylab/classes/animal_behavior/MOVIES.DIR/GRAVIDUM.MOV

Supernormal Releasers Provides crucial clue to process of natural selection.

Since larger eggs more likely to release egg rolling, natural selection should favor genes leading to more potent sign stimuli. Goose eggs should become the size of volleyballs.

But clearly they don't.  Evolution is always a trade off between the pressures of conflicting demands. Egg must represent a balance between a goose's physiology, how large an egg it could lay and incubate, the pressure of sharp-eyed predators, optimum no. of offspring, etc.

Sexual Selection Males often develops structures which are valuable

only in sexual competition for mates. Such structures can be expensive metabolically, be

attractive to predators and unwieldy, For example: fiddler crab claws and peacock tails.

Selection favored ever bigger claws = supernormal releaser, but claw useless for digging, tasty to predators, impede movement and escape. Led to extinction of Irish elk whose antlers were so large and unwieldy, but sexy, that couldn't survive with them. Morphological arms race out of hand. IRM's of females make disarmament out of question.

Sign stimuli as traps We can do experiments that make responses to sign

stimuli look ridiculous. In nature birds do not encounter volleyballs in their nests, so are never tempted to try to hatch them.

Sign stimuli indicate the machinelike nature of some animal behavior. E.g. digger wasps. No contingency plan, asuch as boredom, is built into their genes.

Navigation systems have "backup routines", e.g. "sun not out, use magnetic field", but not these.

Value of Releasers According to early ethologists, releasers and

the accompanying physiological arrangements which --> IRM and its associated motor program, a FAP, = single most general strategy in animal behavior from prokaryotes to primates.

This arrangement dramatically illustrates the innate programmed nature of much behavior.

Value of Releasers

However, the IRM is not an explanation, but is rather a troublesome divisible component of behavior.

Where are they? Why have we found no physiological, neurological evidence of them? etc.

Value of Releasers for early ethologists Proposed IRMs might have evolved before

animals developed the intellectual capacity. to "reason" for themselves. Preserved by the conservative nature of evolution.

IRMs enable animals to react quickly without interference from the time-consuming and error-prone process of thinking.

Could serve to focus animals’ attention. They can ignore irrelevant and confusing stimuli in particularly important situations.

Value of Releasers for early ethologists Could enable animals to perform perfectly some

crucial act, when there is no room for learning because even a small mistake could be fatal.

Could show an otherwise distracted animal exactly what information. it needs to get.

Could have begun as a way to compensate for relatively crude sense organs, e.g. eyes, and have been maintained because they are still useful, even though there has been a tremendous improvement in the sensory  apparatus.

Objections IRMs occasionally trigger responses to cues

which are obviously inappropriate. This results in maladaptive responses which could have been avoided with only a slight increase in IRM specificity.

IRMs in sexual selection can force species such as fiddler crabs (& saber-toothed tiger; giant elk?) into dangerous or even fatal evolutionary paths.

 Sign stimuli and pattern recognition (problems of early ethology) What and where were those all important

IRMs in neural terms? How are they wired to accomplish all they

were supposed to be responsible for? How, since they were so imperfect, could

they have been favored by natural selection?

Sign stimuli and pattern recognition (Neurophysiologists and early ethologists ) Neurophysiologists were no help. None of the

nerve cells they were listening in on could be coding for "eggness" or other pattern recognition functions attributed to IRMs.

Ethologists replied that the neurologists were simply not "listening" to the crucial cells.

The problem lay in the early conception of the IRM.  It was flawed.

Herring gull feeding ( How do chicks identify their parents?) Tinbergen used cardboard models to see

which --> gaping or pecking and where it was directed on the model. Biggest study was done on herring gulls. They are born seeing (most species have nestlings born blind and depend on non visual cues at first (impact of parent on nest critical).

T. concluded from his models that baby birds have a vague, shadowy picture of parents to guide their efforts.  

Tinbergen’s conclusions (continued) Herring gull has a red spot on lower tip of its

bill. Waves downward pointing bill slowly back and forth in front of chicks when it has food for them. T. said there was more than one stimulus to release pecking by chicks.

The relative configuration of head, bill and spot are important.

Tinbergen’s conclusions (continued) Spot on forehead of model --> pecking rate 1/4 that of spot located in normal position. So, T argued, spot not the releaser because either location should work as well.

Chicks using innate picture to direct pecking. Had an inborn idea of what its parents ought to look like. (Same elusive notion of releasers as organized patterns s.a. "eggness", "hawkness", etc pervades early ethology.

Tinbergen’s conclusions (continued) T. also found that a simple stick with a red

ring was a better releaser than the more accurate models. Reinforces doubts re. innate pictures.

So there were many problems with Tinbergen’s conclusions.

Resolution of problem by Jack Hailman Hailman began with the hypothesis that all of

T's results could be explained by conditioning or trial and error learning. Suppose chicks have a pecking reflex and simply learn to associate a food reward with pecking at the parent. No IRM in chicks may be necessary and reactions of chicks to models simply measure how good a picture the chicks have formed through experience.

Resolution of problem by Jack Hailman H. found that parents do have releasers

which trigger and direct pecking of chicks, but demonstrated that learning is a crucial element in the process.

H. showed that pecking accuracy increased with age.

Hailman’s laughing gulls Laughing gulls have a red bill and black

head. H. asked, “what is their releaser? He compared the series of increasingly

schematic models and established a lack of ambiguity for newly hatched chicks of this species. Only the parents bill was important. The bill without a head and neck was as good a releaser as a whole head. Without the bill the head is ignored.

Hailman’s laughing gulls –what is their releaser? Color irrelevant. White head and bill almost

as good as naturally colored one. The orientation and specific movement of

bill crucial. Stationary vertical model twice as effective as a horizontal model. Horizontal movement increased the effect. Vertical movement --> no effect.

The important criteria are an accurate representation of the parent's bill during feeding.

Hailman’s solution (continued) H. used herring gulls with the same results.

The bill and the red spot were important, not the relative configuration (which Tinbergen said was crucial). H. Used naïve checks and found that movement of the red spot not its location is the releaser of pecking.

How did Tinbergen misinterpret his results? T's Dummy heads were mounted on sticks

and moved pendulum-like. Caused bill spot to sweep out a bigger arc and move faster than the forehead spot.

H. showed that chicks actually preferred forehead spots when they were moved at the same rate as the bill spot. Happens because when the forehead is moved faster, the bill appears larger.

How did Tinbergen misinterpret his results? The bill is the secondary releaser. The

isolated bill with spot --> some pecking, so increasing the speed of the bill exaggerated its releasing value and added to the spot, producing the preferred model. This shows that chicks are attending to 2 discrete independent features - not to any patterns of head configuration and spot placement.

How did Tinbergen misinterpret his results? T. overlooked the precise age of the chicks. Both T & H left chicks with parents except for

testing. H. found that after 2 days chicks began to prefer the

sort of configuration T said was innate. H. said it was not innate at all, but the result of learning.

Chicks replaced innately recognize releasers with a picture of parents. Since chicks and parents recognize each other as individuals before the end of a week, one wouldn't expect either one to continue to depend on releasers.

Importance of Hailman's work Releasers are discrete features not

patterns. The features are optimal stimuli for well-

known classes of feature detector neurons in visual and auditory systems of higher animals. 

This means that the animals are immediately responding to stimuli which they are capable of sensing at birth. 

Importance of Hailman's work Moving red spot = ideal stimulus for one class of

cells in a visual system (moving spot detectors). Recognition of horizontally moving bars (swinging

beak) = task of another group (moving bar detectors).

Sensors respond best to an optimal rate of movement. H. found gull chicks similarly tuned (12 cm/sec = optimal rate). Endless examples of such tuning of neural cells to stimuli; e.g. bright center and dark periphery of flowers = optimal stimulus for a class of cells in bees.  Button and

Importance of Hailman's work Releasers are used by animals to recognize

important features of the world because genes can't encode innate neural photographs.  Need such a picture, but don't have it.

Can't recognize prey, predators, etc. at birth. Recognition of crucial entities depends, at least at first, on crude releasers, e.g. bars and spots.

It would be better to have a picture, but they don't, so probably can't encode anything so complex in the genes.

Have to make the best of the situation and gear animals to make use of the sketchy cues they can specify. IRM is vote best system possible with the available hardware.

Importance of Hailman's work Hailman also demonstrated the importance

of learning. Learning can instruct animals to memorize

the appearance of important individuals and objects as soon as possible.

Gull chicks substitute a picture of parents for releasers very soon. Then this image takes over and new IRMs function in releasing and directing begging.

http://www.biology.ucsc.edu/~barrylab/classes/animal_behavior/MOVIES.DIR/GRAVIDUM.MOV