lecture 15 - aggression

7/28/2019 Lecture 15 - Aggression

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AGGRESSIONVERSUS

COOPERATION Aggression and cooperation

have been historically

dichotomized in the behaviorliterature

Many researchers argue over

which is most important tohuman social systems andevolution

This dichotomy is false

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AGGRESSION

Proximate mechanisms

Models of aggression

Experience and aggression

Aggression and the social

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WHY BE AGGRESSIVE?

Defend resources

Mates

Territory

Food

Offspring

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DOMINANCE HIERARCHIES

Typically in social taxa

Provides priority of access toresources withoutconstantfighting

Dominant animals have higherresource holdingpotential

Can operate at several levels...

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FIGHT OR FLIGHT

Surge in adrenaline andnorepinephrine

Increase in blood sugar andoxygen to the brain, skeletalmuscles, and heart

Nonessential systems(digestive, reproductive)

temporarily shut down

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FIGHT OR FLIGHT

Ultimately, when benefits of victory outweigh the costs of fighting, and animal should fight

Proximately, its more complicated:

Dominant individuals secrete more androgens, and are more likely to fight thansubordinates

A history of winning fights increases androgens, and makes future fighting morelikely

Losing increases glucocorticouds, as does submission (although dominantindividuals may also have high glucocorticoids)

If an animal is close to losing, they will give a subordinate response to cut shortthe costs of losing...

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SIGNALING DEFEAT

Example: Atlantic salmon

(Salmo salar) and territorial

aggression

Subordinates have higher

levels of cortisol

Subordinates also develop

darker body coloration, which

dominants remain lighter and

develop a dark eye band

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SEROTONIN AND

AGGRESSION In most mammals (and

humans), low serotonin is linked

with high aggression

In fish, high serotonin is seen insubordinates, leading to lessfighting

Example: Serotonergicactivity and hierarchy inArctic charr (Salvelinusalpinus)

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SEROTONIN AND

AGGRESSION Winberg et al.

Constructed four groups of four fish

Determined stable dominance hierarchy, then disbanded

Then placed all four equal-ranked males in the same groups...

The fish that wound up subordinate in phase two were thosewith elevated serotonergic activity

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SEROTONIN AND

AGGRESSION In lobsters it was quite

different:

Lobsters that lost a fightdidnt fight for daysafterwards, unless injected

with serotonin

Serotonin lead to increasedintensity and duration ofaggression

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GAME THEORY MODELS OF

AGGRESSION Instead of assessing cooperative

potential, youre assessing

willingness to fight or flee

Presumed to be in the contextof defending a resource, sowillingness is contingent upon

resource value

Also contingent uponopportunity costs, and potentialmortality costs

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THE HAWK-DOVE GAME

Maynard Smith & Price (1973)

First real game theoretical model in ethology

Two strategies:

Hawk escalates until it wins or is injured

Dove displays as if it will escalate, butalways retreats if the other escalates

Neither all-hawk nor all-dove is ESS

except under certain conditions

When resource value outstrips cost(V>C), Hawk is ESS

When C>V, neither strategy is ESS, butsome mixture of the two can be

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BOURGEOIS AND ANTIBOURGEOIS

HAWK AND DOVE

Bourgeois: if you own aterritory, be a hawk; if not,be a dove.

Anti-bourgeois: if youown a territory, be a dove; ifnot, be a hawk.

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BOURGEOIS BUTTERFLIESExample: Speckled wood butterflies (Pararge aegeria)

and temporarily sunlit territories, Davies (1978)Tuesday, May 28, 13


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ANTI-BOURGEOIS SPIDERSExample: Territorial accession in the Mexican

spider (Oecobius civitas), Burgess (1976)Tuesday, May 28, 13


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WAR OF ATTRITION MODEL

Important underlying assumptions:

1. Individuals can choose to display aggressively for any length of time

2. Display behavior is costly, and the longer a display the more cost

invoked

3. There are no clear cues (size, territory possession, etc) thatcontestants can use to judge opponent

In this case, the duration is entirely dependent on the value of theresource being contested

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WAR OF ATTRITION MODELESS relies on robability function: (2/V)*e^(-2x/V)

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DUNGFLIES AND THE WAR OF

ATTRITION Females lay eggs in dung pats, males wait

to mate with them... how long should amale wait?

If he leaves too early, he will invoke acost (travel, lost matings); if he stays toolong, he is missing potentialopportunities elsewhere

Parker & Thompson (1980) found thatwhen the cost of flying between patcheswas held constant, stay times at a patchrelated to the number of successfulmatings following the War of Attritionmodel

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SEQUENTIAL ASSESSMENT

MODEL Example: Nannacara anomala,

Enquist et al.

Males form hierarchies, aggressiveinteractions range from color change toapproach to tail beating to biting andmouth wrestling to circling.

Weight is a huge factor... heavier fish wonmore quickly, and fish evenly matched in

weight fought much longer

Males always began with simpler and lessrisky fights, and then escalated to moreaggressive behaviors. Always in the sameorder.

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WINNER AND LOSER EFFECTS

Winner effects: winning

a fight increases theprobability of future wins

Loser effects: losing afight increases theprobability of future losses(more common than winnereffects)

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WINNER AND LOSER EFFECTS

IN BLUE-FOOTED BOOBIES Drummond et al.

Aggression among nestlings is common

If older chicks were dominant andaggressive early on, then they would alwaysbe dominant to younger chicks, even ifyounger chicks got bigger

Pitted dominant and subordinate

individuals against inexperienced sparringpartners to see if this was winner or losereffect

Winner effect waned with time, but losereffect was pervasive and long-lasting

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FITNESS AND WINNER/LOSER EFFECTSExample: Copperhead snakes (Agkistrodon

contortrix),Schuett (1997)Tuesday, May 28, 13


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FITNESS AND WINNER/LOSER

EFFECTS Fights have an effect on mating success, so is

there a fitness effect to winner/loser effects?

Put two unfamiliar males in an arena with afemale. Each male had a 10% size difference,and the larger male always won.

10 winner and 10 losers were chosen,matchedby size with a male with no priorfighting experience

No winner effect (winning males did not winmore often than naive males), but definiteloser effect

Two time losers then pitted against a smallersnake... lost again!

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PROXIMATE WINNER/LOSER

EFFECTS Collected blood from losers

immediately after fight (as well

as winners and controls)

Found significantly highercorticosterone in losers

High corticosterone incopperheads associated withsubordinate behavioranda lackof courtship behavior to femalesin the vicinity of the lost fight

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MATHEMATICAL MODELS OF

WINNER/LOSER EFFECTS In a dominance hierarchy, why would an animal ever accept a subordinate position?

Landau (1951) found that, with only fighting ability a factor, mathematical models did

not support linear transitive hierarchies... only when winner/loser effects were addeddid the models work

Dugatkin (1997) reevaluated these models to see is winner/loser effects causeddifferent hierarchies

Winner effects only caused clear transitive linear hierarchies maintained byaggressive interactions

Loser effects only kept one clear alpha, but very unclear hierarchicalrelationships beneath the alpha since losers avoided open contests

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BYSTANDER EFFECTS

Animals can eavesdrop on thefights of others to assess

competition without actuallyfighting

Example: greenswordtail fish

(Xiphophorus helleri),Earley & Dugatkin (2005)

Evidence for bystander,audience, and loser effects

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PROXIMATE MECHANISMS

AND THE BYSTANDER EFFECT Example: cichlid fish

Osteochromis mossambicus,

Oliveira et al. (2005)

Measured T in urine of males beforeand after watching a fight

Significant increase in T

Increase in T may be adaptive: givethe male better attention, learning,memory that would prove helpful(e.g., if winner attacks eavesdropper)

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AUDIENCE EFFECTS

Individuals in an aggressive interaction alsochange their behavior if theyre being observed

Example: Recruitment screams in

chimpanzees (Pan troglodytes),Slocombe & Zuberbuhler 2007

Screams may be aggressor or victim, reliablydifferent based on who is winning

Looked at Mild vs Severe aggressive interactions

During severe aggressive interactions, victimscreams were much louder and longer when anaudience was present (compared to noaudience), but only when a member of theaudience was of equal or higher rank to theaggressor!

lecture 15 - aggression

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