BIO220-Slides-Lecture4-W2012

BIO220-Slides-Lecture4-W2012 - Alarm Calls Ground squirrel...

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Unformatted text preview: Alarm Calls Ground squirrel altruistic behavior Meerkat 1 Cooperative breeding help other individuals reproduce 2 Eusociality division of labor, 3 Social Behaviour • Definitions • Game theory • Evolutionary explanations of cooperative behaviour • Reciprocity • Group selection • Kin selection 4 Social Behaviour The interaction with and responses to other individuals of the same species Altruistic: Behaviour increases another individual’s reproductive success at a cost to one’s own reproductive success Eg. alarm calls Cooperative: Behaviour that, if adopted by two (or more) individuals, benefits both 5 Cooperation and Natural Selection “… a special difficulty, which at first appeared to me insuperable, and actually fatal to my theory” Charles Darwin 1859 How then can cooperative genotypes spread in an environment of selfish genes? 6 Game Theory Developed during the Cold War • economics • evolutionary biology John Nash 7 Explanation of Game Theory • Some number of players • Set of possible strategies • Some pay-off schedule for playing A against B for all A and B 8 Hawk - Dove Game Contest between two individuals over obtaining a resource Two strategies that can be used: Hawk (fight aggressively) Dove (resolve contest peacefully) 9 Hawk/Dove Game 2 players 2 strategies/player Pay off matrix John Maynard Smith Dove R = Reward C = Cost of fighting Dove Hawk what does the dove get if it played against a dove? R/2 R Hawk 0 R/2 - C 10 Which strategy will prevail? 11 Suppose R > 2C; e.g., R=6, C =2 Can cooperative strategy win? Dove R/2 3 Dove R Hawk Hawk 0 0 R/2 - C 6 1 It is always best to play Hawk! 12 Suppose R < 2C; e.g., R=2, C =6 Hawk Dove R/2 0 1 Dove R Hawk 2 0 R/2 - C -5 • If Hawk is common, Dove is best • If Dove is common, Hawk is best To compete will lose a lot Might expect a mixture at equilibrium Fitness is Frequency-Dependent It depends on the the strategies others are playing 13 Social Behaviour • Definitions • Game theory • Evolutionary explanations of cooperative behaviour • Reciprocity • Group selection • Kin selection 14 Reciprocity • Given multiple encounters perhaps it does not pay to be selfish • Can examine this possibility using Iterated Prisoner’s Dilemma 15 Evolution of Reciprocity (with repeated encounters) Bill Robert Axelrod Iterated Prisoner’s Dilemma Best strategy is “Tit for Tat” I. Cooperate on the first encounter II. Copy your opponents last move thereafter Anatol Rapoport 16 Elements of the Tit for Tat Strategy? ‘Nice’ - start by cooperating ‘Retaliatory’ - stop if partner stops cooperating ‘Forgiving’ - if partner has cheated in past but “changes” then cooperate 17 Predator Inspection 18 Predator Inspection in Guppies risk themselves to inspect if sth is a predator Two fish approaching a predator can be viewed as a an iterated prisoner’s dilemma At each point in time, each individual can: (a) Continue towards the predator (cooperate) (b) Hold back (defect) Predator Inspection in Guppies copy their partner's last move QUESTION: EXPERIMENT: Do guppies play Tit-for-Tat during predator inspection? Examine predator inspection behaviour with “cooperating” and with “defecting” partner 20 Experimental Set-up 1 fish only cooperating mirror will move very close to predator 21 Experimental Setup defecting mirror will defect as well 22 Distance to Predator Results Defecting mirror Cooperating mirror defecting partner: defect as well cooperating partner: closer 1234 5 6 7 8 9 10 Minutes 23 Social Behaviour • Definitions • Game theory • Evolutionary explanations of cooperative behaviour • Reciprocity • Group selection • Kin selection 24 Crows use tools have culture, dialects. Crow 25 Individual Selection on Alarm Calling Callers Population before selection Selection Population after selection Noncallers callers decrease in frequency 26 Crows gather social group 27 28 Group Selection on Calling many non caller alleles in the temporary group low many calling alleles high int. everyone is looking out for everyone. selection at the group level is for the callers. selection at the individual level is against the callers. predation is biased toward the calling allele. calling crows are eaten. Non-callers Callers 29 Evidence for Group Selection? Impatiens capensis 30 OBSERVATIONS Large plants out-compete small plants Small plants are still very common Question: Why don’t large plants take over the population? Hypothesis: Groups with many large “selfish” plants do worse than groups with many small “cooperative” plants 31 Flower Number Results among individual among groups Size 32 Results • Large individuals in well spaced groups tended to have high fitness. • Groups consisting of many small individuals tended to have high fitness. • These two effects tend to cancel one another out. 33 Kin Selection “the difficulty…is lessened, or as I believe disappears, when it is remembered that selection may be applied to the family, as well as to the individual, and thus may gain the desired end” - Charles Darwin 1859 altruism and kin selection 34 Social Behaviour • Definitions • Game theory • Evolutionary explanations of cooperative behaviour • Reciprocity • Group selection • Kin selection 35 Altruism directed toward a random individual Altruist allele Non-altruist allele no benefit no benefit no benefit Non-altruists do best 36 Chimpanzees 37 Blue bird nestlings 38 altruist allele Altruism directed toward a genetic relative Altruist allele if cost<benefit, altruism wins Non-altruist allele Altruists might do best 39 Hamilton’s Rule c = Cost of altruism to the actor b = Benefit of altruism to the recipient Bill R = Genetic coefficient of relatedness (Probability that the recipient carries the altruist gene) 1 bR>c R is usu. <1, if it's a distant relative, benefits have to be very large. 40 Hamilton’s Rule bR>c We expect greater altruism to be directed towards closer genetic relatives 41 Alarm Calling In Ground Squirrels OBSERVATION: • Individuals give predator alarm calls • Callers are at high risk (cost) • Group benefits from warning QUESTION: Do squirrels with close relatives nearby give more calls than those without? is the altruistic allele aware of itself being nearby? 42 Proportion of time calling Results 0.5 0.4 0.3 0.2 No close relatives Close relatives Offspring 0.1 43 “I would happily give my life for 2 siblings, 4 grandchildren, or 8 cousins.” J.B.S.Haldane 44 Evolution by Natural Selection Differential reproductive success of genes Natural selection cannot favour self sacrificial genes Favoured genes ALWAYS increase in frequency each generation 45 Next Lecture: Parent-Offspring Conflict 46 ...
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