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Agonistic behaviour is any
social behaviour Social behavior is behavior among two or more organisms within the same species, and encompasses any behavior in which one member affects the other. This is due to an interaction among those members. Social behavior can be seen as similar to an ...
related to
fighting Combat ( French for ''fight'') is a purposeful violent conflict meant to physically harm or kill the opposition. Combat may be armed (using weapons) or unarmed ( not using weapons). Combat is sometimes resorted to as a method of self-defense, or ...
. The term has broader meaning than
aggressive Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...
behaviour because it includes threats, displays, retreats, placation, and conciliation. The term "agonistic behaviour" was first implemented by J.P Scott and Emil Fredericson in 1951 in their paper "The Causes of Fighting in Mice and Rats" in ''Physiological Zoology.''
Agonistic An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agon ...
behaviour is seen in many animal species because resources including food, shelter, and mates are often limited. Some forms of agonistic behaviour are between contestants who are competing for access to the same resources, such as food or mates. Other times, it involves tests of strength or threat display that make animals look large and more physically fit, a display that may allow it to gain the resource before an actual battle takes place. Although agonistic behaviour varies among species, agonistic interaction consists of three kinds of behaviours:
threat A threat is a communication of intent to inflict harm or loss on another person. Intimidation is a tactic used between conflicting parties to make the other timid or psychologically insecure for coercion or control. The act of intimidation for co ...
,
aggression Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...
, and
submission Deference (also called submission or passivity) is the condition of submitting to the espoused, legitimate influence of one's superior or superiors. Deference implies a yielding or submitting to the judgment of a recognized superior, out of re ...
. These three behaviours are functionally and physiologically interrelated, yet fall outside the narrow definition of aggressive behaviour. While any one of these divisions of behaviours may be seen alone in an interaction between two animals, they normally occur in sequence from start to end. Depending on the availability and importance of a resource, behaviours can range from a fight to the death or a much safer ritualistic behaviour, though ritualistic or display behaviours are the most common form of agonistic behaviours.


As studied in rodents

Scott and Fredericson describe that agonistic behaviour is displayed in a variety of different circumstances in response to different stimuli. Scott and Fredericson studied mice and rats, and classified three main categories of agonistic behaviour these animals display, which include preliminary behaviour, attack, and defensive and escape behaviour. Preliminary behaviour describes the behaviours displayed by these rodents if fighting does not immediately begin. These may include involuntary behaviours such as hair-fluffing, where the rodent's hair stands up on end with no prominence on a particular region of the body, or tail-rattling where the rodent's tail experiences muscle contraction and twitches from side to side, making a loud sound if struck against a hard object. Another preliminary agonistic behaviour demonstrated by mice is referred to as mincing behaviour which is when mice circle their opponent before a fight begins. The fight itself is classified as one of the pattern of behaviour that occurs and involves physical violence between the rodents. Finally, the defensive and escape behaviour occurs usually immediately after the fight and is displayed by the mouse that was defeated in the fight. The defeated mouse, if allotted space, will run away and try and take shelter from the victorious mouse. If it is not possible for the mouse to physically run and escape because space is not available, the defeated mouse will rear up on its hind legs and hold its front legs up in a way that is characterized as a "submissive stance". These are examples of the physical behaviours that are responses to conflict in mice.


Evolution and ecology of agonistic behaviour: Stomatopoda (praying mantis shrimp)

Agonistic behaviour is a result of
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
, and this can be studied in a number of species facing different environmental pressures. Though agonistic behaviours can be directly observed and studied in a laboratory setting, it is also important to understand these behaviours in a natural setting to fully comprehend how they have evolved and therefore differ under different selective pressures.
Mantis shrimp Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in lengt ...
, predatory
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s, are an example of an aggressive and territorial organism whose agonistic behaviour has been studied in an ecological and evolutionary context. Mantis shrimp are among the world's most aggressive crustaceans. These sea creatures are secretive, but highly alert and active predators who inhabit burrows and cavities along coral reefs, rocky coasts, and muddy shores of tropical and subtropical waters. Roy Caldwell and Hugh Dingle conducted research on mantis shrimp and other
stomatopod Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in leng ...
s, which focused on the evolution of agonistic behaviour and how it applies to the ecology of these organisms. Agonistic behaviour has co-evolved alongside biotic factors such as body morphology, competition both within the species and against other species, and the habitats that these shrimp inhabit. Stomatopods arose from
leptostraca Leptostraca (from the Greek words for ''thin'' and ''shell'') is an order of small, marine crustaceans. Its members, including the well-studied ''Nebalia'', occur throughout the world's oceans and are usually considered to be filter-feeders. It ...
n stock, as is indicated by fossil evidence, approximately 400 million years ago.
Morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
of stomatopods is consistent with most
malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobst ...
ns in that they have three main body segments: the
cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino s ...
, the
thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
and the
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
. The abdomen is made up of six segments, five of which possess a pair of
pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...
s, which are used for respiration and swimming. The key appendage used by stomatopods for fighting behaviour is referred to as the
raptorial The term ''raptorial'' implies much the same as ''predatory'' but most often refers to modifications of an arthropod's foreleg that make it function for the grasping of prey while it is consumed, where the gripping surfaces are formed from the o ...
appendage, which is actually a pair of enlarged second maxillipeds just behind the
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
e. These strong maxillipeds are used for purposes of prey capture in addition to fighting. The morphology of this appendage, particularly the propodus and dactyl which extend forward in such a way that resembles the striking appendage of a praying mantis, gives this crustacean its name. Caldwell et al. classified the raptorial appendage into two categories based on its functional purpose: a smashing appendage or a spearing appendage. The smashing appendage is possessed by members of
gonodactylidae Gonodactylidae is a family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of it ...
and the dactyl contains several short spines. The spearing appendage is possessed by squillids, lysiosquillids, bathysquillids, and a couple gonodactylids; the last group contains both spearers and smashers. "Smashers" are able to use the raptorial appendage with such a force, particularly the gonodactylids, that they are able to smash the glass of double walled aquariums in the laboratory. These smashers are able to use this immense force to kill same-species competitors with one blow. Caldwell et al. describe how two stomatopods generally display severe fighting behaviour when they have an encounter, both between species and within the same species, and males and females display the same level of this behaviour except in breeding season. Most species of stomatopods, regardless of the type of appendage, ordinarily deliver blows during agonistic encounters with the dactyl closed. When the dactyl is open, the result is usually serious injury or death of the opponent. These crustaceans may deliver blows with the dactyl open but generally only in situations of extremely intense fighting displays, which are rare amongst most species. Behaviour that is common during agonistic displays is raptorial appendage display, which is a common behaviour across many taxa. Display and expansion of the raptorial appendage is conducted in order to make the animal appear larger and therefore more threatening to competitors in times of agonistic encounters, and comparable displays in other taxa include teeth baring in canines or horn display in ungulates. This display behaviour is an evolutionarily conserved behaviour in agonistic displays. Evolutionary differences are clear in "smasher" and "spearer" stomatopods who inhabit different substrates and either burrow or do not burrow. Caldwell et al. describe these differences with respect to a behavioural display called a "meral spread". This behaviour is described by these researchers as the most extreme of raptorial appendage displays, and is defined by the elevation of the
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
and
antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...
e and antennules while the raptorial appendage itself is elevated and spread. Interestingly, this meral spread may be displayed dozens of times during an agonistic encounter and Caldwell et al. explain it is used as a method to inhibit actual physical violence. An evolutionary divergence between stomatopods is described in appearance of the meral spot, which is a dorsal, medial groove on the raptorial merus of the raptorial appendage. Smasher stomatopods, which are species that tend to inhabit cavities within rocks or coral, have brightly coloured meral spots which aid in making the meral spot more visible during these meral spread displays in fights. These bright meral spots possessed by smashers are either yellow, blue, red or white and are outlined by a conspicuous black pigment. Conversely, spearing Stomatopods or some smashing species that do not inhabit rock or coral cavities, have much duller meral spots. This correlation suggests to researchers that habitat and meral spot colouration have co-evolved, and those that inhabit burrows possess these bright spots and those species that do not have dull spots. This demonstrates how ecology and evolution of organisms within the same order directly affects agonistic behaviour.


Hormonal influence

Agonistic behaviour is influenced by the action of hormones such as
vasopressin Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travel ...
, which is a small peptide synthesized in the brain by magnocellular neurons. Agonistic behaviour itself may be divided into two categories: offensive or defensive. Each of these classes of agonistic behaviour are the result of different neurobehavioural pathways, and offensive and defensive agonistic behaviour are elicited by different stimuli. Offensive behaviour specifically has been studied in the context of intruder interactions in studies employing rodents as test subjects. For example, when an unfamiliar male hamster is placed into cage of a conspecific male, a stereotypical suite of agonistic behaviours follow. The resident male approaches the intruder and sniffs him intently, threatens the intruder with an upright posture, and finally initiates a physical attack on the intruder. The resident male attacks the belly of the intruder male and attempts to maneuver the intruder onto his back. Studies have shown that offensive behaviour displayed by hamsters may be modulated due to the presence of vasopressin. Specifically, research conducted by Ferris et al. (1990) suggests that when a vasopressin receptor antagonist is injected into the anterior
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
of the resident male, the tendency to attack intruder males decreases as the dose of antagonist increases. This antagonist has been known to decrease the tendency of offensive aggression via injections into the ventrolateral hypothalamus, therefore is able to act on multiple regions of the brain and exhibit the same effects of offsetting this agonistic behaviour. While vasopressin plays a role in offensive aggression in agonistic behaviour,
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...
also plays a role in aggressive behaviour in rodents as well as similar effects in humans. Research has shown that increased levels of serotonin or stimulating serotonic receptors in rodents corresponds with decreased agonistic behavioural display, such as behaviours like attacking and biting. Male resident hamsters, which typically always display stereotypical offensive agonistic behaviours, display a significant decrease in bite attempts toward intruder males when treated with a serotonin reuptake inhibitor called fluoxetine. Vasopressin and serotonin both play significant roles in agonistic behavioural displays, and understanding the interaction of these two opposing neurotransmitters is important in fully understanding the neurobiology of agonistic behaviour. It is understood that vasopressin enhances aggression in agonistic displays due to increased activity in the neural pathways that are associated with increased flank marking and the offensive aggression demonstrated in resident hamsters in the presence of an intruder. This neural pathway that enhances aggression is subdued by the presence of serotonin. It is hypothesized that serotonin acts as an antagonist to vasopressin by eliciting its effects on vasopressin-sensitive neurons and therefore inhibiting these neurons. Steroid hormones are also associated with offensive aggression behaviour.
Androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
s in particular have well documented effects on enhancing aggression in male rodents, and
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
injections into the
septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...
and medial pre-optic area of castrated mice greatly increased offensive aggression.
Glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
s also have reported effects on agonistic behaviour in mice, though these effects are not as thoroughly understood as effects of androgens. Research has demonstrated that in mice that have been defeated in agonistic encounters have elevated levels of
corticosterone Corticosterone, also known as 17-deoxycortisol and 11β,21-dihydroxyprogesterone, is a 21-carbon steroid hormone of the corticosteroid type produced in the cortex of the adrenal glands. It is of minor importance in humans, except in the very rare ...
, which appears to enhance submissive behaviour and therefore has opposing effects on agonistic aggressive behaviour.


Prediction of winning

The type of agonistic behaviour observed, whether it be aggressive or submissive, all depend on the likelihood of winning. For instance, size is usually a good predictor of fighting success, and many animals will display to flaunt their size. Animals are better able to assess their next form of agonistic action by judging the opponent's size and if they are likely to win a fight if a physical altercation were to occur.


Example: Stalk-eyed flies ''(Diopsidae)''

In aggressive behaviour by male
stalk-eyed flies Stalk-eyed flies are insects of the fly family Diopsidae. The family is distinguished from most other flies by most members of the family possessing "eyestalks": projections from the sides of the head with the eyes at the end. Some fly species fr ...
the males "square off" by displaying their eyes. Females show a strong preference for mating with males with longer eyestalks. Due to the female preference, males have evolved to compete with each other for mating rights. In the threat display the two flies face each other head-to-head, with their forelegs spread outward and parallel to the eyestalks. This behaviour allows each individual to judge the distance between its competitor's eyes. Eyestalk length increases with body size, and males with shorter eyestalks will usually retreat. A further distance between the eyes conveys a bigger body size, and a better chance of winning.


Avoidance

Physical fighting is actually rare between animals. It would seem that normally the more aggressive an animal is, the more it has to gain. However, in a normal scenario if an animal is too aggressive it might face an unacceptably high cost such as severe injury or death. Unless an animal has a sure indication that they will win without injury, or the resources are valuable enough for the risk of death, animals usually avoid fighting. An animal must weigh the relative costs and benefits of fighting. If the costs are too high, avoiding a fight is preferable.


Ritual display

For animals,
display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...
is any behaviour modified by evolution that is used to convey information. Animals display particular signs, which recipients can use to infer something about the mental and physical state of the first animal. To avoid the heavy cost of fighting, animals have evolved sophisticated rituals, which they use to bluff their opponents into backing down or fleeing. The cost-benefit model of display makes three assumptions: (1) type of display varies depending on the cost; (2) the risk of the display increases as the effectiveness of display increases; and (3) the value of resource being disputed over determines the choice of display used. Animals have evolved to use their physical attributes as a display of ability. If contests can be resolved with ritual display, fighting is not needed. Display can be used to dispute for mates,
territory A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
, and food through symbolic gestures instead of battles to the death. If an animal can display without fighting that he is more physically fit than his opponent, he will have gained more than he would have if he had fought and in the process possibly been injured.


Example: Male grey catbird (''Dumetella carolinensis'')

Male
grey catbird The gray catbird (''Dumetella carolinensis''), also spelled grey catbird, is a medium-sized North American and Central American perching bird of the mimid family. It is the only member of the "catbird" genus ''Dumetella''. Like the black catbird ...
s fluff their feathers and spread their lower tails to defend their territory when threatened by another male. The bird that is capable of puffing up and appearing to be the biggest will win the territory.


Example: Western gorilla (''Gorilla gorilla'')

Male
western gorilla The western gorilla (''Gorilla gorilla'') is a great ape found in Africa, one of two species of the hominid genus ''Gorilla''. Large and robust with males weighing around , the hair is significantly lighter in color than the eastern gorilla, ''G ...
s display a wide range of both vocal and gestural communications when threatened by an opponent. A silverback (
alpha male In biology, a dominance hierarchy (formerly and colloquially called a pecking order) is a type of social hierarchy that arises when members of animal social groups interact, creating a ranking system. A dominant higher-ranking individual is som ...
) will start hooting, throwing, chest pounding, leg kicks, and sideways running when approached by another male. This is done to intimidate the opponent and show physical abilities without actually making any physical contact.


Threats

Threat behaviour is any behaviour that signifies hostility or intent to attack another animal. Threat behaviour is meant to cause the opponent to back down and leave. While ritual display can be used for an array of reasons or communicative purposes, threat distinctly is meant for hostility and is the last step before fighting or submission. Threat does not involve physical contact with another animal. Any threat behaviour most often elicits other agonistic behaviour in the recipient. This initiation of threat will result in a display of physical attributes, a fight, or submission; the behaviour or sequence of behaviours depends on what resources are being fought over and each individual's chance of winning against his opponent. In any animal species, threat always contains components of attack and fleeing, which expresses an animal's readiness and likelihood of winning. An intimidation display with a means to threat are exhibited through: hair bristling, feather ruffling, raising skin folds and crest, teeth displaying, horn displaying, making sound, etc.


Example: Frill-necked lizard (''Chlamydosaurus kingii'')

''
Chlamydosaurus kingii The frilled lizard (''Chlamydosaurus kingii''), also known as the frill-necked lizard or frilled dragon, is a species of lizard in the family Agamidae. It is native to northern Australia and southern New Guinea. This species is the only member o ...
'', an Australian
agamid Agamidae is a family of over 300 species of iguanian lizards indigenous to Africa, Asia, Australia, and a few in Southern Europe. Many species are commonly called dragons or dragon lizards. Overview Phylogenetically, they may be sister to the I ...
lizard, uses its frill as a way to display size and aggression to opponents. It is one of the largest and most notable displays seen in the animal kingdom. In comparison to its body size, the frill can flare out to make the lizards head look several times bigger, and it displays bright orange and red scales. Males of ''C. kingii'' fight and display frills often during the mating seasons. The male ritualistic display includes repeated partial erections of the frill, head bobbing, tail lashing, and waving of forelimbs.


Agonistic fighting

Actual fighting in contests is rare because of the risk of injury to both participants. It is most likely to occur when individuals are similarly sized, or when the contested resource is essential for reproduction or survival. Even when agonistic behaviour escalates to fighting, restraint may be used. Fish such as
Oreochromis mossambicus ''Oreochromis'' is a large genus of oreochromine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range and are important in aquaculture. Many others have ver ...
often exhibit aggressive displays, but rarely fight to the point of injury or bodily harm. This is also the case in fights among some male venomous snakes; they wrestle, but refrain from biting.


Example: Black mamba (''Dendroaspis polylepis'')

Agonistic fighting for
black mamba The black mamba (''Dendroaspis polylepis'') is a species of highly venomous snake belonging to the family Elapidae. It is native to parts of sub-Saharan Africa. First formally described by Albert Günther in 1864, it is the second-longest ...
s involves a wrestling match in which opponents attempt to pin each other's head repeatedly to the ground. Fights normally last a few minutes but can extend to over an hour. The purpose of fighting is to secure mating rights to receptive females nearby during the breeding season.


Submissive behaviour

Submissive behaviour involves an individual indicating by an act or posture that it will not challenge a dominant individual in a social group. Submissive behaviours are part of the maintenance of a dominance hierarchy of cooperating individuals in a social group that have overlapping but not entirely coincident interests.


Example: Bearded dragon (''Pogona vitticeps'')

Communication Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inquir ...
between animals is often achieved by adding a succession of behaviours to a display. Social interactions among
bearded dragon ''Pogona'' is a genus of reptiles containing six lizard species which are often known by the common name bearded dragons. The name "bearded dragon" refers to the underside of the throat (or "beard") of the lizard, which can turn black and gain we ...
s (''Pogona vitticeps'') consist of a unique set of movements or visual signals. Waving is one of the most visible signs of submission one lizard can display to another. The lizard rests on three of its legs, raises one of the front arms and then slowly waves the arm in a circular motion. This circular motion, along with the dragon puffing up slightly, shows submission. This display is seen between opponents, as well as adolescents towards adults.


See also


References

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