Aggression

what is aggression

• An unprovoked attack

• Hostile, injurious or destructive behavior or outlook, especially when caused by frustration

• Combative readiness

aggression in general

• Aggression can be beneficial: winning a mate, food, or territory

• Aggression can be costly

• Energy expenditure

• Injury, death

• Loss of a mate, food, or territory

• Aggression and associated fighting among animals within the same species are damaging

• But this is a means of selection, particularly among males, to give the strongest, healthiest within a group the opportunity to sire more offspring and to contribute their genes to the next generation

• Animals kept in isolation are often aggressive: fear, lack of “social graces”
• Animals can be trained to fight or to be passive
• Mother or conspecific group during rearing can have a profound effect on aggressive tendencies in adulthood
• Is “road rage” an environmental situation or a genetic situation?
• There is certainly an environmental aspect to aggression

types of aggression

• Social

• Territorial

• Predatory

• Pain-induced

• Fear-induced

• Irritable

• Maternal

• Sexual

aggression within or between species

• Within a species: social aggression

• Possession conflict (mate, home area, water hole, feeding area, salt lick)

• Between species

• Prey - predator relationship

• Territorial conflict (home area water hole, feeding area, salt lick)

Lorenz (“On Aggression”) Theory

motivation to fight is similar to motivation to eat or drink, building up over a period of time, and then being released as expression of the behavior

• The accumulated drive is discharged by fighting

This theory suggests that aggression is inevitable

is aggression heritable?

• Roosters have been selected for fighting ability for thousands of years (Rupert, 1949)

• Outlawed in all states

• There may be more intense and more effective selection against submissiveness than for aggressiveness

• A rooster that “runs” in the pen will be killed as will all of his family members

• Is selection against submissiveness more effective than selection for aggressiveness?

is aggression heritable? → chickens

• Chickens raised together in stable social groups from a very young age can actually live together: “social inertia” [the resistance to change or the endurance of stable relationships in societies or social groups (Guhl, 1962)]

But, if a fight in such an all-male flock begins, it will not end until there is just one survivor

correlated responses to selection for aggression

• Stamina is an important characteristic

• Architecture of the blood vessels and extremely short blood coagulation and prothrombin times contribute to stamina (game birds)

• Tunica media and adventitia of veins in game birds: considerably thicker than those of domestic cocks

fighting mice

Ginsburg and Allee, Physiol. Zool. 15:485, 1942

• Trained some mice to not fight by handling them gently prior to putting them together

• Trained other mice to fight by allowing them first to be attacked by dominant mice and then to put them with helpless mice whom they attacked

• Similar to training methods for fighting dogs, cocks, etc

• Putting non-fighting mice together: they lived peacefully and had no obvious dominance hierarchy

• Putting fighting mice together: they fought, and the loser was then chased by the victor any time they were re-introduced to each other → dominance hierarchy was developed based on fighting

socially dominant mice

have stronger mPFC (medial prefrontal cortex) excitatory synapses compared with subordinates

the fine line between aggression and sex

Mating in chickens begins as an aggressive act

• A rooster will approach another bird (male or female) in an aggressive manner

• The response of the approached individual governs whether the encounter ends in a fight, a sexual encounter or just ends

sequence of events: two males

• If a rooster approaches another rooster, challenging or waltzing, the second rooster may:

1. signal submissiveness through body language, defusing the encounter

2. remain neutral: the initiating rooster can continue to press for a fight, or he can lose interest

3. respond with his own challenging or waltzing: it will ignite a conflict

sequence of events: a male and a female

• A rooster will approach a hen in much the way he would another rooster

• His initial approach is one of aggression: upright posture,

waltzing

• The direction the encounter takes depends on the hen’s response to the rooster’s advance

• The hen, generally a much smaller and less aggressive individual, may:

1. escape: she is not interested in the encounter; the male will lose interest.

2. simply move aside: expressing disinterest; the male will lose interest.

3. crouch: a sexual response, inviting the male to cease aggression and begin sexual activities

sequence of events: two females

This encounter will follow similar possibilities to that of the encounter between two roosters

• Upon approach by one hen, the second may avoid, appear neutral or challenge the first

• Within a stable social group, these encounters may actually be conducted with very little apparent movement or flurry

• Once established, the dominance hierarchy allows individuals to avoid actually fighting