Mechanisms of Animal Behaviour

What is Animal Behaviour?

Animal behaviour is the study of the activities and responses shown by animals in relation to their environment and other organisms. It includes all the actions that animals perform during their life such as searching for food, finding shelter, avoiding enemies, communication and reproduction. These activities help the animal to survive and maintain its life in a particular habitat. Animal behaviour generally occurs as a response to different stimuli which may arise from external environment such as sound, smell or light, or from internal conditions like hormonal changes. From an evolutionary point of view, many behaviour patterns are developed through natural selection because those behaviour that increase survival and reproduction are more likely to persist in the species. The behaviour of animals may be of two types– innate behaviour and learned behaviour. Innate behaviour are instinctive and inborn which the animal can perform without prior experience, while learned behaviour develop through experience and interaction with the environment. The scientific study of natural behaviour of animals in their environment is referred to as ethology.

Mechanisms of Behaviour

The different mechanisms by which behaviour is produced and controlled in animals are as follows–

1. Neural control and reflex arc– Behaviour is mainly controlled by the nervous system of animals. The sensory receptors detect the stimulus from environment and transmit the signals to the central nervous system through sensory neurons. The central nervous system then sends signals through motor neurons to the effector organs such as muscles or glands which produce the response. The simplest form of this mechanism is reflex action which is a rapid and involuntary response to a stimulus.
2. Fixed action patterns (FAPs) and innate releasing mechanisms (IRMs)– Fixed action patterns are complex sequences of innate behaviour that are genetically determined. These behaviour are initiated by specific external stimuli called sign stimuli or releasers. The stimulus is recognized by the nervous system through an innate releasing mechanism which acts as a neural filter and triggers a sequence of behavioural actions that usually continue until completion.
3. Central pattern generators (CPGs)– Central pattern generators are specialized neural circuits present in the nervous system which produce rhythmic motor activities automatically. These neural networks coordinate repeated movements such as walking, swimming, breathing and flying without continuous sensory input.
4. Orientation mechanisms (kinesis and taxis)– Animals often move in response to environmental stimuli through orientation mechanisms. Kinesis is the random movement of an animal where the rate of movement or turning changes according to the intensity of a stimulus. Taxis is a directed movement either towards or away from a stimulus such as light, chemicals or temperature.
5. Non-associative learning– This mechanism involves change in behaviour when an animal is repeatedly exposed to a single stimulus. Habituation is the gradual decrease in response to a repeated harmless stimulus. Sensitization is the increased responsiveness when an organism is exposed to a strong or harmful stimulus.
6. Associative learning– In this mechanism animals learn by forming association between different events. Classical conditioning occurs when a natural reflex becomes associated with a new stimulus. Operant conditioning occurs when a voluntary behaviour is modified by its consequences such as reward or punishment.
7. Imprinting– Imprinting is a special type of learning which occurs during a critical period early in life. In this mechanism young animals quickly learn and recognize certain objects or organisms, usually the mother, and form a strong behavioural attachment.
8. Observational learning and insight– Some animals are capable of learning by observing the behaviour of other individuals. This type of learning is referred to as observational learning. In certain animals higher cognitive ability allows problem solving or insight where the animal can perform a behaviour without repeated trial and error.

Neural Control and Reflex Arc

The mechanism of neural control and reflex arc in behaviour are as follows–

• Sensory receptors– These are specialized cells that detect the stimulus from the internal or external environment. The stimulus may be light, temperature, pressure, chemicals or sound. The receptors convert the stimulus into nerve impulses.
• Afferent (sensory) neurons– The impulses produced by sensory receptors are transmitted to the central nervous system through sensory neurons. These neurons carry the information from receptors to the brain or spinal cord.
• Interneurons– Interneurons are present in the central nervous system. These neurons connect the sensory neurons with motor neurons and help in processing the information received from receptors.
• Efferent (motor) neurons– After processing the stimulus, the central nervous system sends signals through motor neurons. These neurons carry the commands from the brain or spinal cord to the effector organs.
• Effector organs– The effector organs include muscles or glands. These organs receive the signals from motor neurons and produce the final response such as movement or secretion.
• Reflex arc– Reflex arc is the pathway followed by nerve impulses during a reflex action. It is the simplest form of neural control where the response is rapid and involuntary.
• Types of reflex arc
  • Monosynaptic reflex arc – It is the simplest reflex pathway where the sensory neuron directly connects with the motor neuron through a single synapse.
  • Disynaptic reflex arc – In this type one interneuron is present between sensory and motor neuron forming two synapses.
  • Polysynaptic reflex arc – It is a complex reflex pathway involving several interneurons and many synapses.
• Characteristics of reflex action
  • Latency – It is the short delay between the stimulus and the response.
  • Summation – Weak stimuli can combine together to produce a reflex response.
  • Warm-up – The strength of reflex response may gradually increase when the stimulus continues.
  • Inhibition – Some muscles are inhibited so that opposite actions do not occur during reflex movement.
  • Fatigue – Repeated stimulation of reflex may reduce the response due to exhaustion of neurons.

Fixed Action Patterns (FAPs) and Innate Releasing Mechanisms (IRMs)

The mechanisms involved in fixed action patterns and innate releasing mechanisms are as follows–

• Fixed action patterns are innate behavioural sequences that are genetically programmed in animals. These behaviour are instinctive and do not require prior learning or experience. Once the behaviour begins it usually proceeds in a fixed sequence.
• A fixed action pattern is always triggered by a specific external stimulus which is called sign stimulus or releaser. This stimulus is recognized by the animal and initiates the behavioural response.
• Once a fixed action pattern is initiated the animal continues the sequence of actions until it is completed. The behaviour may continue even if the original stimulus disappears during the action.
• Fixed action patterns are generally common to all members of the same species. These behaviour are inherited and show very little variation among individuals.
• In greylag goose if an egg moves outside the nest the sight of the egg triggers a behaviour where the goose rolls the egg back to the nest using its beak. Even if the egg is removed during the action the goose still completes the egg rolling movement.
• Innate releasing mechanism is the internal neural system present in the brain which recognizes the sign stimulus and activates the fixed action pattern.
• The innate releasing mechanism acts as a neural filter that detects the correct stimulus from the environment and sends signals to initiate the behavioural response.
• The innate releasing mechanism can combine different aspects of a stimulus such as shape, colour and movement. When these stimuli reach a threshold level the fixed action pattern is released.
• Innate releasing mechanisms are associated with specific neural networks present in the central nervous system which help in recognizing the stimulus and producing the behavioural action.

Central Pattern Generators (CPGs)

The mechanisms and characteristics of central pattern generators are as follows–

• Central pattern generators are specialized neural circuits present in the nervous system. These neural networks produce rhythmic and repetitive motor activities automatically.
• Central pattern generators are capable of producing rhythmic movements without continuous sensory input or conscious control from higher brain centres.
• These neural circuits control repeated motor activities such as walking, swimming, flying, breathing and swallowing.
• Central pattern generators are located in different regions of the central nervous system. CPGs controlling respiration and swallowing are mainly present in the brain stem while those controlling locomotion are distributed in the spinal cord.
• Some neurons present in the neural circuit act as pacemaker neurons. These neurons generate rhythmic electrical signals which help in producing repeated motor patterns.
• In many rhythmic movements two groups of muscles work alternately. This is controlled by reciprocal inhibition where one group of neurons becomes active while the other group is inhibited.
• Although CPGs can function independently they also receive sensory information from the environment. This feedback helps in adjusting movements according to environmental conditions.
• Higher brain centres can modify or override the activity of central pattern generators. For example animals can consciously change their breathing pattern or walking movement.
• Central pattern generators are present in many groups of animals including invertebrates and vertebrates. These neural circuits help animals perform important repetitive movements required for survival.

Orientation Mechanisms (Kinesis and Taxis)

The different orientation mechanisms used by animals to respond to environmental stimuli are as follows–

• Orientation refers to the ability of animals to control their position and movement in space in response to environmental stimuli. Animals use different sensory signals from the environment to move or adjust their posture.
• Kinesis is a type of movement where the response of the animal depends on the intensity of the stimulus rather than its direction. The movement is generally random.
• In orthokinesis the speed of movement of the animal changes according to the intensity of the stimulus. For example woodlice move faster in dry conditions to reach a more humid environment.
• In klinokinesis the rate of turning of the animal changes with the intensity of the stimulus. Animals with a single receptor often show this type of movement when searching for favourable conditions.
• Different types of kinesis may occur depending on the type of stimulus. For example photokinesis occurs in response to light while chemokinesis occurs in response to chemicals.
• Taxis is a directional movement of an animal either towards or away from the source of a stimulus. The movement occurs in a specific direction.
• Types of taxis based on stimulus– Different types of taxis are observed depending on the stimulus such as phototaxis (light), chemotaxis (chemicals), geotaxis (gravity) and rheotaxis (water current).
• Klinotaxis
  In klinotaxis the animal compares the intensity of stimulus by making alternate side movements. This type of orientation is common in organisms having a single sensory receptor.
• Tropotaxis
  In tropotaxis the animal uses two sensory receptors to detect the stimulus from both sides. This allows the animal to move directly towards or away from the stimulus source.
• Telotaxis
  In telotaxis the animal is exposed to two different stimuli but it chooses only one stimulus and moves towards it.
• Menotaxis
  Menotaxis is a type of orientation where the animal maintains a constant angle with respect to the stimulus source such as the sun.
• Mnemotaxis
  In mnemotaxis animals use memory of landmarks and surroundings to navigate and reach a particular location. This type of orientation is commonly observed in some insects.

Non-Associative Learning

The mechanisms involved in non-associative learning are as follows–

• Non-associative learning is a simple type of learning in which the response of an animal changes after repeated exposure to a single stimulus. In this type of learning the animal does not associate the stimulus with reward or punishment.
• Habituation is the gradual decrease in response of an animal when the stimulus is repeated many times and the stimulus is harmless or irrelevant.
• Habituation helps the animal to ignore unimportant stimuli from the environment. This allows the animal to conserve energy and focus on important signals.
• Habituation occurs due to reduction in neurotransmitter release at the synapse. Because of this the nerve impulse transmitted to the effector organs becomes weaker.
• Sensitization is the increase in responsiveness of an animal after exposure to a strong or harmful stimulus.
• In sensitization certain neuromodulators increase the release of neurotransmitters at the synapse. This strengthens the response of the nervous system to the stimulus.
• Dishabituation occurs when a previously habituated response returns to its original level after the introduction of a new strong or novel stimulus.
• Non-associative learning allows animals to modify their behaviour according to environmental conditions and helps them respond appropriately to important stimuli.

Associative Learning

The mechanisms involved in associative learning are as follows–

• Associative learning is a type of learning in which an animal learns to associate two different stimuli or events. Through this process the behaviour of the animal is modified according to experience.
• Classical conditioning is a form of associative learning where a natural reflex becomes associated with a new stimulus.
• In classical conditioning a neutral stimulus is repeatedly paired with an unconditioned stimulus which naturally produces a response. After repeated association the neutral stimulus alone is capable of producing the response which is then called conditioned response.
• In the experiment conducted by Ivan Pavlov dogs were trained to associate the sound of a bell with the presentation of food. After repeated pairing the dogs started salivating when the bell was rung even in the absence of food.
• Operant conditioning is another type of associative learning in which an animal associates its voluntary behaviour with a particular consequence.
• In this mechanism the behaviour of an animal is strengthened when it is followed by a reward and weakened when it is followed by punishment.
• In experiments conducted by B.F. Skinner a rat placed inside a box learned to press a lever to obtain food. The reward increases the probability that the rat will repeat the behaviour.
• Associative learning helps animals modify their behaviour based on experience and environmental conditions which improves survival and adaptation.

Imprinting

The mechanisms and characteristics of imprinting are as follows–

• Imprinting is a special type of learning which occurs early in the life of an animal. This learning depends on certain innate mechanisms present in the nervous system.
• Imprinting occurs only during a short and specific developmental stage called the critical period. During this period the young animal is highly sensitive to particular stimuli.
• Once imprinting occurs the learned behaviour becomes permanent and generally cannot be reversed later in life.
• Young animals do not have complete knowledge of their mother at birth. Instead they possess an innate tendency to respond to the first moving object that shows certain features such as movement and sound.
• During imprinting the young animal forms a strong behavioural attachment with the object on which it imprints. This object is usually the mother.
• In greylag geese the newly hatched goslings follow the first moving object they see. If a human is present during the early period the goslings may imprint on the human and follow that person.
• Konrad Lorenz demonstrated imprinting by incubating goose eggs and allowing the goslings to see him first after hatching. The goslings imprinted on Lorenz and followed him instead of their mother.
• Imprinting helps the young animals remain close to their parents which provides protection, food and learning of important survival behaviour.
• Imprinting has been used in wildlife conservation to guide young birds during migration. For example some birds are trained to follow aircraft so that they can learn their migration route.

Observational Learning and Insight

The mechanisms involved in observational learning and insight are as follows–

• Observational learning is a type of learning in which an animal acquires new behaviour by observing the actions of other individuals.
• In this mechanism the animal watches the behaviour of another individual and then copies or imitates that behaviour.
• When a learned behaviour spreads within a group through observation it is referred to as cultural transmission. The behaviour may continue in the population for many generations.
• In some Japanese monkeys individuals learned to wash their food before eating it. Other monkeys observed the behaviour and gradually adopted the same habit.
• Insight is a higher level learning process in which an animal solves a problem through reasoning and understanding rather than repeated trial and error.
• In insight learning the solution to a problem appears suddenly after the animal understands the situation.
• Chimpanzees have been observed to stack boxes or objects in order to reach food placed at a higher level.
• Some animals such as chimpanzees use tools to obtain food. For example they may use sticks to remove insects from holes.
• Certain birds such as crows are able to use or modify objects as tools to obtain food from difficult places.
• Observational learning and insight allow animals to acquire complex behaviours and adapt more effectively to their environment.

Importance of Studying Mechanisms of Animal Behaviour

The importance of studying mechanisms of animal behaviour are as follows–

1. Understanding of neural mechanisms– The study of behavioural mechanisms helps in understanding how the nervous system receives stimuli and produces appropriate responses in animals.
2. Knowledge of brain function– By studying behaviour in animals the basic principles of brain activity and neural circuits is understood.
3. Study of neuropsychiatric disorders– The mechanisms of behaviour helps researchers in studying disorders such as autism, anxiety and depression.
4. Understanding neurodegenerative diseases– Research on simple reflex behaviour in animals has provided information about diseases related to memory loss and aging such as Alzheimer’s disease and Parkinson’s disease.
5. Development of medical treatments– The knowledge obtained from animal behaviour studies helps in developing new medical therapies for disorders of the nervous system.
6. Spinal cord injury research– The study of neural circuits such as central pattern generators helps in understanding the control of movement which is useful for treatment of spinal cord injuries.
7. Technological development– The mechanisms of animal behaviour have contributed to the development of robots and machines capable of moving in complex environments.
8. Improvement of sensory technologies– Studies on animal sensory systems such as echolocation in bats and sound detection in owls helps in the development of sonar and radar technologies.
9. Understanding evolutionary adaptations– The mechanisms of behaviour explain how different behavioural patterns have evolved through natural selection.
10. Understanding ecological interactions– The study of animal behaviour helps in understanding how animals find food, avoid predators and interact with their environment.

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