Chap.14 Aggression 鄭先祐 (Ayo) 教授 國立台南大學 環境與生態學院 生態科學與技術學系 環境生態研究所 + 生態旅遊研究所

Ayo 2010 Ethology2 Aggression  Fight or flight?  Game theory models of aggression  The Hawk-Dove Game  The war of attrition model  The sequential assessment model  Winner, loser, bystander, and audience effects

Ayo 2010 Ethology3 Aggression  Conflict → fight or flight?  Dominance hierarchies (rank orderings of the individuals) in a group.  Intruder aggression (Fig. 14.1)  When a wasp (left) approaches a nest, guards at the nest determine whether it ’ s a hive mate or an intruder. Intruders are aggressively repelled.

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5 Fight or flight?  If fighting is costly, then once it is clear that an animal is losing a fight, it will often be beneficial for it to signal subordination, and hence reduce future costs.  It may inhibit its aggressive behaviors.  Color change may be particularly good communication vehicle in aggressive contests, where color may be linked to “badges of status”, and hence color change can quickly indicate an individual’s relative rank in a hierarchy and whether it will engage in aggressive behaviors. (Fig. 14.2) (Atlantic salmon)

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7 Serotonin and aggression  In crustaceans, increased serotonergic function leads to enhanced aggression and high social status.  案例：  when lobsters are paired up in fights, they generally escalate their aggressive behaviors through a series of ritualized combats.  Once an individual loses a fight, however, it avoids aggressive interactions for days.  But losers can be made more aggressive if they are given injections of serotonin (Fig. 14.3)

Ayo 2010 Ethology8 Fig serotonin and aggression .A small individual was made subordinate by being matched against an individual that was 30% larger than it was.  When serotonin was continuously infused into subordinates (red bar), their aggressive levels surged. Subordinates returned to their pre- infusion levels within 30 minutes after serotonin infusions were turned off.  (A) the intensity of the aggression over time, and (B) the duration of the aggression.

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10 Game theory models of aggression  All game theory models must have some sort of variable that represents the value of the resource being contested.  Deciding to fight (Fig.14.4)  (A) one of the many resources animals will fight over is food, as shown here by these vultures that are fighting over a carcass.  (B) males also fight over females, here, male elephant seals are fighting over access to reproductively active females.

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Ayo 2010 Ethology12 Value of a resource  Two individuals contesting a resource may not assign the same value to that resource.  For example (Fig. 14.5), imaging that two animals – one of whom is starving, and the other of whom is hungry, but not starving – are contesting a ten-pounds of meat.  To a starving animal, ten-pounds of food might make the difference between life and death, while to a less hungry animal the value of the ten pounds of meat might be much lower.

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Ayo 2010 Ethology14 Territory  Consider the value of territory to a potential intruder and to a territory holder  The territory holder will value a contested area (its territory) more because it has already invested time and energy in learning where the resources in such a territory are located  Table 14.1 Resource value and fighting.  The value that an individual animal assigns to some resource affects how long contests last to what extent they escalate.

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Ayo 2010 Ethology16 The hawk-dove game  Imagine that individuals can adopt one of two behavioral strategies when contesting some resource:  (1) hawk- wherein a player will escalate ( 增加占有 ) and continue to escalate until either it is injured or its opponent cedes( 讓出 ) the resource,  (2) dove – wherein a player displays as if it will escalate, but retreats and cedes the resource if its opponent escalate.

Ayo 2010 Ethology17  V = the value of the contested resource  C = the cost of fighting

Ayo 2010 Ethology18 Evolution of fighting behavior: game theory  Why don’t animals always fight with maximum effort?  Natural selection favors the individual that passes on more of its genes  Game theory can help to understand the evolution of conflict  Game theory: predicts an animal’s optimal behavior  While taking into account the behavior of other animals

Ayo 2010 Ethology19 The game-theory model  Players: the combatants  Strategies: Different decisions available to players  Assumed to be heritable  Successful strategies increase in the population  Payoff: measures the costs and benefits for each strategy  Currency: used to measure the payoff  Relates to fitness (number of offspring produced or number of calories acquired)  A payoff matrix: organizes the values of the payoffs of each strategy against the other strategies

Ayo 2010 Ethology20 One game theory model: hawk-dove  The simplest game-theory model of aggression  Two players fight over a resource  Each opponent can play one of two strategies: hawk and dove  Hawk strategy: immediately attack its opponent  Dove strategy: flee immediately if confronted by a hawk  Display if confronted by another dove  If a hawk meets a hawk or a dove meets a dove  Each opponent has a 50% chance of winning

Ayo 2010 Ethology21 The payoff matrix for the hawk-dove game  Three variables measure a currency that relates to fitness:  V = the value of the resource being contested  W = the cost of being wounded in a fight  D = the cost of displaying to an opponent  Add some numbers:  V = 30  W = 60  D = 5

Ayo 2010 Ethology22 Payoff for hawk – hawk interaction  If an animal playing the hawk strategy meets another hawk  Both attack immediately  One hawk wins the resource: its payoff is V  The other hawk will be wounded: its payoff is –W  The average payoff for a hawk vs. hawk interaction  Payoff for the winning hawk + the payoff for the losing hawk  Divide by 2 to get the average  V – W 2

Ayo 2010 Ethology23 Payoffs for other interactions  Hawk against dove  The hawk immediately attacks  The dove flees  Hawk wins the resource, so its payoff is V  Dove against hawk  The dove immediately flees  The dove does not get injured  Nor does it win anything - its payoff is 0

Ayo 2010 Ethology24 The payoff for dove vs. dove  One wins the resource  The other walks away  Both pay the cost of display  The payoff for the winning dove is V-D  The payoff for the losing dove it is just –D  Sum these and divide by 2  V ─ D ─ D V ─ 2D V = = ─ D 2 2 2

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Ayo 2010 Ethology27 Box18.1 How many hawks and doves?  Neither hawk nor dove is an evolutionarily stable strategy.  Rather, the stable equilibrium composition of the population is some combination of hawks and doves in a mixed ESS.  The stable proportion of hawks and doves occurs when the average payoff for the hawk strategy equals the average payoff for the dove strategy.  Assume:  p = the proportion of hawks in a population  1- p = the proportion of doves

Ayo 2010 Ethology28 Box18.1 How many hawks and doves?  Payoff for dove strategy =  p (V-W)/2 + (1-p) V  Payoff for hawk strategy =  p (0) + (1 – p) (V/2 – D)  At equilibrium….  -15p + (1-p)30 = 0 + (1-p) 10  -15p p = 10 – 10p  30 – 45p = 10 – 10p  20 = 35 p  p = 0.57

Ayo 2010 Ethology29 Understanding the game  The currency = units of fitness  These strategies are heritable  Successful doves have offspring  That also play the dove strategy  Hawks give rise to hawks  Game-theory models predict whether strategies in a population  Increase in frequency  Remain stable  Or disappear

Ayo 2010 Ethology30 An evolutionarily stable strategy (ESS)  A strategy that, when played by all members of the population  Cannot be invaded by another strategy  If the dove strategy is an ESS  All members of the population play the dove strategy  If an animal playing hawk entered  All of its opponents would be doves  The hawk strategy will do well  The hawk’s genes increase  The hawk strategy increases in frequency

Ayo 2010 Ethology31 Is the hawk strategy an ESS?  Will the population eventually become all hawks?  If the population is comprised of all hawks  The average payoff drastically decreases  If a dove enters the population  It won’t win  But it won’t be wounded during half its battles  The frequency of the dove strategy would increase  Neither a “pure hawk” strategy nor a “pure dove” strategy is an ESS

Ayo 2010 Ethology32 A mixed ESS is stable  A mixed ESS: some combination of hawk and dove strategies that is stable  The stable proportion of hawks and doves occurs  When the average payoff for the hawk strategy equals the average payoff for the dove strategy  A certain proportion of animals always plays hawk  And another proportion always plays dove  Or all animals play both hawk and dove

Ayo 2010 Ethology33 Can a hawk or dove strategy be stable?  If the value of a resource (V) is greater than the cost of being wounded (W)  A pure hawk strategy is an ESS  If V < W, a mixed ESS will result  A pure dove strategy is never an ESS

Ayo 2010 Ethology34 Bourgeois butterflies  In the Speckled wood butterfly, territories are not set in space.  That is, rather than having territory with a set place in three dimensions, a male has a territory that is an open patch defined by well- lit areas that emerge when the sun breaks through the clouds.  When a male comes upon an empty well-lit patch, he immediately occupies it and secures a mating advantage, compared to males not in sunlit territories.  Resident wins rule (Fig. 14.6)

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Ayo 2010 Ethology36 Antibourgeois Mexican spiders  These spiders establish their territories under rocks, and when an intruder approaches a territory, the territory holder flees rather than fighting.  The former territory holder then searches for a new territory.  Fig reverse bourgeois strategy

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Ayo 2010 Ethology38 The war of attrition ( 磨損 ) model  Three underlying assumptions  (1) individuals can choose to display aggressively for any duration of time  (2) display behavior is costly – the longer the display, the more energy expended  (3) there are no clear cues such as size, territory possession, and so forth, that contestants can use to settle a contest.  Fig 14.8 the probability that a contest will last a certain length of time is a function of the value of the resource.

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Ayo 2010 Ethology40 The sequential assessment model  A third game theoretical model of aggression is called the sequential assessment model.  The sequential assessment game examines contests in which the level of aggression varies from relatively mild to very dangerous.  範例：  In Nannacara anomala (fighting fish) (Fig )  Mouth wrestling (Fig )

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Ayo 2010 Ethology42 Mouth wrestle in fighting fish

Ayo 2010 Ethology43 Winner, loser, bystander, and audience effects  Winner and loser effects  In blue-footed boobies  In Rivulus marmoratus (fish)  In copperhead snakes  Mathematical models  Bystander effects  Audience effects

Ayo 2010 Ethology44 Blue-footed boobies  Fig winning and losing booby chicks  (A) when subordinate chicks (green curve) who have experienced many losses are paired against neutral singleton chicks (red curve), they display very little aggressive behavior.  (B) when dominant chicks (orange curve) who have recently won many aggressive interactions are paired against neutral chicks (red curve), they are very aggressive. The pattern begins to dissipate after four hours.

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Ayo 2010 Ethology47 In Rivulus marmoratus (hermaphroditic fish)  More controlled experimental studies of winner and loser effects have been undertaken in fish than in any other group.  Why?  (1) aggression is common in fish  (2) aggression in fish is easily quantified in controlled laboratory settings  (3) the endocrinology of aggression in fish has been well documented in numerous species.

Ayo 2010 Ethology48 In Rivulus marmoratus  Wins (W), losses (L) or neutral (N)  The wins and losses an experimental fish received before it was tested were controlled by the researchers.  By comparing fish in the WW versus LW and LL versus WL treatment (Table 14.3), the penultimate aggressive interaction a fish experiences also affects its current probability of winning or losing.

Ayo 2010 Ethology49 In Rivulus marmoratus  While penultimate interactions were important, their impact on winning or losing a current interaction was not as powerful as the outcome of the interaction immediately preceding the interaction underway.  asymmetry in winner and loser effects- that is, the loser effect was not stronger than the winner effect, nor vice versa.

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Ayo 2010 Ethology51 In copperhead snakes  Copperhead snakes (Agkistrodon contortrix)  Males had had no aggressive interactions for 6 to 12 months prior the study.  “size” contests  Two males that differed in size by approximately 10 %.  In all 32-trials, the larger male emerged as dominant and gained reproductive access to the female.  Winner and loser effects  Ten winners and ten losers from the “ size ” contests, and each was matched against a same-sized male copperhead that had no prior experience.

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Ayo 2010 Ethology53 In copperhead snakes  No winner effects  The prior winners were not more likely to win again.  But have a loser effects,  that is, losers were more likely to lose again.  losers lost all contests even with smaller opponents.  The plasma corticosterone was significantly greater in losers than in winners or controls (Fig )

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Ayo 2010 Ethology55 Mathematical models  Computer simulation that examined winner and loser effects when individuals assessed each other’s fighting ability and could choose to fight or flee.  Results: (Table 14.14)  Winner effects alone produce hierarchies in which the rank of individuals all the way from top rank (α) to bottom rank can be unambiguously assigned.  Loser effects alone produce hierarchies in which a clear αindividual exists, but the relationship among other group members remains murky.

Ayo 2010 Ethology56 Table 14.4 winning, losing, and hierarchy formation  When winner effects alone are at play (green box), a clear linear hierarchy exists, with the position of each individual clearly delineated.  When loser effects alone are at play (orange box), only the alpha individuals is clear.  Loser effects tend to outweigh winner effects (red box)

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Ayo 2010 Ethology58 Bystander effects  When the observer of an aggressive interaction between two other individuals changes its assessment of the fighting abilities of those it has observed, the bystander ( 旁觀者 ) effect - sometimes called the “eavesdropper ( 偷聽者 ) effect” – is in operation.  案例： green swordtail fish

Ayo 2010 Ethology59 Bystander effects of swordtails  Eavesdroppers could either observe aggressive interaction between a pair of other or such interactions were blocked from view by an opaque partition.  When eavesdroppers were then paired against winners of the previous contests, those who had observed the previous contests were less likely to (A) initiate interactions, and (B) escalate aggressive interactions.  Those who were paired with the losers were more likely to initiate aggressive contests.  The difference between orange and green bars for losers was not statistically significant.

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Ayo 2010 Ethology61 Cichlid fish  When eavesdropping males watch a fight between a pair of other males, their androgen levels rise (Fig ).  Testosterone levels increased

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Ayo 2010 Ethology63 Audience effects  Individuals involved in appressive interactions change their behavior if they are watched.  Fig audience effects in chimpanzees.  Chimpanzees that were victims in severe aggressive interactions emitted distinctive screams.  Significantly longer screams were emitted when fights were watched by an audience that to the aggressor (orange bars) than when the audience did not contain such an individual (green bars).  This screaming strategy was successful, as victims who emitted longer and more intense screams were able to entice support from observers, who would proceed to intervene and break up fights.

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