Behavior

                            Behavior 


Behavior is action that alters the relationship between an organism and its environment.
Behavior may occur as a result of

• an external stimulus (e.g., sight of a predator)
• internal stimulus (e.g., hunger)
• or, more often, a mixture of the two (e.g., mating behavior)

It is often useful to distinguish between

• innate behavior = behavior determined by the "hard-wiring" of the nervous system. It is usually inflexible, a given stimulus triggering a given response. A salamander raised away from water until long after its siblings begin swimming successfully will swim every bit as well as they the very first time it is placed in the water. Clearly this rather elaborate response is "built in" in the species and not something that must be acquired by practice.
• learned behavior = behavior that is more or less permanently altered as a result of the experience of the individual organism (e.g., learning to play baseball well).

Examples of innate behavior:

• taxes
• reflexes
• instincts

Reflexes

The Withdrawal Reflex

When you touch a hot object, you quickly pull you hand away using the withdrawal reflex.These are the steps:

• The stimulus is detected by receptors in the skin.
• These initiate nerve impulses in sensory neurons leading from the receptors to the spinal cord.
• The impulses travel into the spinal cord where the sensory nerve terminals synapse with interneurons.
• Some of these synapse with motor neurons that travel out from the spinal cord entering mixed nerves that lead to the flexors that withdraw your hand.
• Others synapse with inhibitory interneurons that suppress any motor output to extensors whose contraction would interfere with the withdrawal reflex.

Instincts

Instincts are complex behavior patterns which, like reflexes, are

• inborn
• rather inflexible
• valuable at adapting the animal to its environment

They differ from reflexes in their complexity.The entire body participates in instinctive behavior, and an elaborate series of actions may be involved.
The scratching behavior of a dog and a European bullfinch, shown here, is part of their genetic heritage. The widespread behavior of scratching with a hind limb crossed over a forelimb in common to most birds, reptiles, and mammals. (Drawing courtesy of Rudolf Freund and Scientific American, 1958.)
So instincts are inherited just as the structure of tissues and organs is. Another example.

• The African peach-faced lovebird carries nesting materials to the nesting site by tucking them in its feathers.
• Its close relative, the Fischer's lovebird, uses its beak to transport nesting materials.
• The two species can hybridize. When they do so, the offspring succeed only in carrying nesting material in their beaks. Nevertheless, they invariably go through the motions of trying to tuck the materials in their feathers first.

Interaction of Internal and External Stimuli

Instinctive behavior often depends on conditions in the internal environment.In many vertebrates courtship and mating behavior will not occur unless sex hormones (estrogens in females, androgens in males) are present in the blood.
The target organ is a small region of the hypothalamus. When stimulated by sex hormones in its blood supply, the hypothalamus initiates the activities leading to mating.
The level of sex hormones is, in turn, regulated by the activity of the anterior lobe of the pituitary gland.
The drawing outlines the interactions of external and internal stimuli that lead an animal, such as a rabbit, to see a sexual partner and mate with it.

Releasers of Instinctive Behavior

So once the body is prepared for certain types of instinctive behavior, an external stimulus may be needed to initiate the response. N. Tinbergen (who shared the 1973 Nobel Prize with Konrad Lorenz and Karl von Frisch) showed that the stimulus need not necessarily be appropriate to be effective.

• During the breeding season, the female three-spined stickleback normally follows the red-bellied male (a in the figure) to the nest that he has prepared.
• He guides her into the nest (b) and then
• prods the base of her tail (c).
• She then lays eggs in the nest.
• After doing so, the male drives her from the nest, enters it himself, and fertilizes the eggs (d).
• Although this is the normal pattern, the female will follow almost any small red object to the nest, and
• once within the nest, neither the male nor any other red object need be present.
• Any object touching her near the base of her tail will cause her to release her eggs.

It is as though she were primed internally for each item of behavior and needed only one specific signal to release the behavior pattern.
For this reason, signals that trigger instinctive acts are called releasers. Once a particular response is released, it usually runs to completion even though the stimulus has been removed. One or two prods at the base of her tail will release the entire sequence of muscular actions involved in liberating her eggs.
Chemical signals (e.g., pheromones) serve as important releasers for the social insects: ants, bees, and termites. Many of these animals emit several different pheromones which elicit, for example, alarm behavior, mating behavior, and foraging behavior in other members of their species.
The studies of Tinbergen and others have shown that animals can often be induced to respond to inappropriate releasers. For example, a male robin defending its territory will repeatedly attack a simple clump of red feathers instead of a stuffed robin that lacks the red breast of the males.
Although such behavior seems inappropriate to our eyes, it reveals a crucial feature of all animal behavior: animals respond selectively to certain aspects of the total sensory input they receive. Animals spend their lives bombarded by a myriad of sights, sounds, odors, etc. But their nervous system filters this mass of sensory data, and they respond only to those aspects that the evolutionary history of the species has proved to be significant for survival.