Behavior

Behavior

Animal behavior includes the actions and reactions of animals to external stimuli. The study of animal behavior involves two main approaches: answering questions about how an animal does something (proximate questions) and why an animal does something (ultimate questions). Though humans have always observed animals behave, animal behavior did not become a field of study until the 1930s, when it was called ethology .

Behavior is determined by both genetics and environmental factors, and is controlled by neural mechanisms. Thus, all animals with nervous systems are capable of behavior, including extremely simple ones such as the flatworm, Caenorhabditis elegans, which responds to light. The study of animal behavior is expanding rapidly and includes taxa and subjects too numerous to list here. Major divisions of the field include learning, cognition, and social behavior.

Founders of animal behavior studies include scientists Karl von Frisch, Konrad Lorenz, and Niko Tinbergen, whose work in the 1930s won them a shared Nobel Prize in 1973. Their work focused on how animals can do things they have never before seen done, which is a proximate question relating to the genetics that determine some of an animal's makeup and the physiology that allows the animal to perform the feat.

Their work also included elements of ultimate questions, and it is the answers to these "why" questions that lead us to fully understand the driving force behind the evolution of the behavior. Using the C. elegans example given above, questions about how the flatworm avoids light will be answered by geneticists and physiologists studying light sensors and locomotion capabilities. Why the flatworm avoids light relates to things like evolution (its ancestors avoided light, and it increases an individual's fitness for survival to do so) and environment (predators can detect flatworms better in the light). These ultimate questions helped link the fairly new study of behavior to established disciplines of evolution and ecology , and gave birth to the field we know today as behavioral ecology.

Behavior is a phenotypic trait , and, as with other such traits, an individual's behavior is determined through both genetics and environment. There are few examples of a trait that is strictly determined through just one of these routes, though through rigorous study we can tease apart the genetic and environmental components that determine a behavior.

For example, when a gene for a complex behavior such as alcoholism is reported, it usually means that there has been an abnormal allele of a gene found in some large percentage of alcoholics tested, and that the presence of this allele may somehow make the individuals with it more likely to be alcoholics. It does not indicate, however, that all people with that allele are alcoholics or that all alcoholics have that allele. There are many social factors such as depression and stress that contribute to alcoholism.

Behavior is controlled by the nervous system. Nerve cells acquire sensory cues from the environment, such as light in the case of C. elegans, and convert them to electrical signals that are transported to a central decision-making location, such as a nerve ganglion in C. elegans or the brain in a higher animal. There it will be determined whether the received stimulus demands a reaction. From there, another electrical signal will be sent back out to the target where the response will occur, such as a muscle that controls locomotion and performs the actual behavior.

Learning

One loosely defined category of animal behavior is learning, and this includes imprinting, kin recognition, associative learning, and play. During learning, behaviors are changed based on what an individual sees or experiences.

Imprinting is irreversible learning that occurs during a specific time in an individual's development. Documented in both mammals and birds, one type of imprinting is the recognition and bond that develops between the parent and child in the first few days after birth. A famous example of this occurred when Konrad Lorenz divided a clutch of goose eggs in half, and allowed half of them to incubate with their mother and the other half in an incubation chamber. Those in the first half displayed normal behavior, following their mother around and ultimately interacting and mating with other geese. Those in the second half spent their first few hours with Lorenz and the baby geese imprinted on him. Even when these geese were later reintroduced to their mother and siblings, they showed no recognition but instead always followed Lorenz around and even later showed courtship behavior toward humans. This experiment shows the importance of the critical period in which imprinting occurs (the first few hours of life in this case) and the irreversibility of what is learned, even when the species that is imprinted (a human in this case) is incorrect.

Another example of imprinting includes recognition of kin. At an early age, odors of the nest and early companions are used as cues that let animals recognize who their kin are. Documented even in insects, this kin recognition can be used to explain interactions later in life (significantly after separation from the nest) in which an animal treats another one like a relative if it smells like the nest from which it originated. This may be an important part of kin selection, which is discussed in the final, social behavior paragraph of this entry.

Other types of learning, such as associative learning, are not dependent on a critical period, though the learning may happen most efficiently if taught at a certain time. Associative learning is simply the ability to associate one stimulus with another. One example is trial-and-error learning, where as a result of a certain behavior and its outcome, a good or bad association is learned. Whether an association is positive or negative ultimately leads to the repetition or avoidance of the behavior. Food choices may fall under this category, where the sampling of different food types may lead to satisfaction and nourishment or bad taste and sickness.

Finally, play can be viewed as a type of learning in which capturing prey and social behavior are practiced. Though play is usually done with siblings and without the actual goals of hunting to kill or establishing social and mating hierarchies, the actions practiced in play allow these skills to be practiced for use later on.

Cognitive Behaviors

A second group of behaviors that can be loosely gathered together are cognitive behaviors. These are complex behaviors that involve the perception, storing, processing, and use of information.

Long-distance travel is an example of this complex process. Whales, butterflies, and birds travel thousands of kilometers to return to the exact same spot they were the year before. Migrating animals use several mechanisms including orientation, piloting, and navigation. Orientation involves moving in a certain compass direction, which can be known from cues like stars and the Sun, although some animals can detect magnetic north without these cues.

Piloting is employed for short distances. It involves moving between landmarks such as rivers and mountains that are familiar from past migrations.

Navigation is the most complex. It involves both determining present location in relation to other known locations and using orientation to get to the next destination. This means the animal must create a mental map that is spatially correct in order to plot out the next course.

Social Behaviors

A third group of behaviors is related to social living. Examples include communication, cooperation, and competition. Communication can be between species, such as when a dog snarls to expose its teeth to warn a potential attacker what may be in store. Frequently, communication occurs among species and can be aural such as bird song or cricket chirp; olfactory , such as a spot where an animal urinates; visual; or tactile .

Communication serves a myriad of purposes, including defining territories, attracting mates, telling where a food source is, or warning of impending danger. Cooperation is when two or more individuals work to perform a single task. Many times this task may seem more beneficial to one individual than the other, in which case the individual getting less or no benefit is termed altruistic. Examples of cooperation are in food finding, child rearing, and standing watch for predators.

In many cases of apparent altruism, it is found that the individual receiving the benefit is related to the one giving, such that the one giving is actually helping to preserve a genetically related line. This phenomenon is called kin selection and serves to propagate related genomes , an act that is not purely altruistic.

Competition occurs when a limited resource needs to be divided among individuals. An example of a resource to be divided is territory. Frequently, males must establish a territory that has good food or is a good mating or nesting spot so that they are preferentially chosen by females for mating. Those males who accomplish this are the most successful in passing on their genes. Competition for territory can take the form of violent contests with other males, and even after the territory is won it may need vigilant guarding to keep intruders out.

see also Acoustic Signals; Behavioral Ecology; Communication; Courtship; Social Animals; Sociobiology.

Jean K. Krejca

Bibliography

Alcock, John. Animal Behavior, 6th ed. Sunderland, MA: Sinauer Associates, 1998.

Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. Biology, 5th ed. Menlo Park, CA: Benjamin Cummings, 1999.

Halliday, Tim. Animal Behavior. Norman: University of Oklahoma Press, 1994.

Lorenz, Konrad. King Solomon's Ring. New York: Harper & Row, 1952.

Maier, Richard A., and Barbara M. Maier. Comparative Animal Behavior. Belmont, CA: Brooks/Cole Publishing, 1970.

Mellgren, Roger L., ed. Animal Cognition and Behavior. New York: North-Holland Publishing Company, 1983.

Wilson, Edward O. Sociobiology: The New Synthesis. Cambridge, MA: The Belknap Press of Harvard University Press, 1975.