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Recipient’s fitness Actor’s fitness increases decreases Cooperation AltruismSpite Selfishness Types of social action

Altruism An act that increases the fitness of another individual at a cost to the actor (individuals not related).

33% of young bats fail to feed each night Only 7% of adults fail to feed. Chronic threat of starvation among vampire bats since they can only survive 3 days without a meal! Successful bats will regurgitate part of their blood meal for group members that were not successful – but not randomly! Bats only give to those from whom they have received blood in the past. Wilkinson, G.W Reciprocal food sharing in the vampire bat. Nature. 308: ) Reciprocal Altruism?

Prisoner’s Dilemma Player A / Player B outcomes = D/C > C/C > D/D > C/D

Prisoner’s Dilemma Player A best strategy is to defect but only if B cooperates, therefore cooperation becomes stable.

Prisoner’s Dilemma - modified for previous experience. Tit for tat - remember previous outcome and adjust your behavior accordingly. Nice - both players cooperate on the first move Retaliatory - a player defects if an individual defected before Forgiving - a player cooperates with a past defector that has now chosen to cooperate.

A key component for this to work is individual recognition!

NYTimes Study of Social Interactions Starts With a Test of Trust April 1, 2005 In a finding that could help explain why a sucker never gets an even break, scientists are reporting today that they have succeeded in visualizing feelings of trust developing in a specific region of the brain. In the study, pairs of anonymous subjects were strapped into magnetic resonance imaging scanners 1,500 miles apart. The participants played 10 consecutive rounds of a risk-taking game that involved balancing monetary profit and trust. While they played, the scanners, synchronized through the Internet, measured how the subjects' brains reacted

Camponotus hyatti; Alex Wild Kin Selection

Kin Selection & Hamilton’s Rule Altruism is favored when: rB - C > 0 r = relatedness between altruist and recipient B = fitness benefit to recipient C = fitness cost to the altruist

Relatedness A measure of genetic similarity that arises from shared ancestry. Pedigree relatedness - direct links via bloodlines - produces genetic similarity due to common ancestry - difficult for organisms to assess history

Relatedness: the proportion of alleles, on average, that two individuals share. Relationshipr Identical (monozyotic) twins1 Parent-offspring0.5 Fraternal (dizygotic) twins0.5 Full siblings0.5 Half siblings0.25 Step siblings0 non-relatives0

In pied kingfisher, primary helpers deliver more help (fish) and are more closely related to breeders than secondary helpers.

Relatedness within a population When individuals share alleles at a higher frequency than randomly selected individuals, r is positive. When individuals share alleles at the same frequency a randomly selected individuals, r = 0. When individuals share alleles at a lower frequency than randomly selected individuals, r is negative. Important to consider effective population size…

Other factors that reduce selfish behavior Kin selection - increases indirect fitness of individuals. Repression of competition - the success of the group is increased with competition occurs between groups, not among group members. Synergistic mutualism/obligate symbiosis Delayed benefits - give up something now for later fitness benefits (e.g. reciprocal altruism).

7. Eusociality Reproductive division of labor (sterile workers). Overlapping generations. Cooperative brood care. Examples include: Hymenoptera (all ants, some bees & wasps; >12 origins) Isoptera (termites; 1 or 2 origins) aphids ambrosia beetles some naked mole rats

How can worker sterility spread, or be maintained, when w=0? How can altruism evolve? “But with the working ant we have an insect differing greatly from its parents, yet absolutely sterile; so that it could never have transmitted successively acquired modifications of structure or instinct to its progeny. It may well be asked how is it possible to reconcile this case with the theory of natural selection?” C.D.

The haplo-diploid Hymenoptera A B CB C BC A B A CA C

r between sisters = 0.75 r between mother & daughters = 0.50 Workers are more closely related to sisters than daughters (when singly mated, single queen colony). The haplo-diploid Hymenoptera

Potentially provides an explanation for: Kin selection within social groups why eusociality arose >12 times in Hymenoptera, but only 1-2 times in Isoptera. why workers are female in Hymenoptera, but both sexes in Isoptera. …but the principles of kin selection remain important and instructive. Potential problems: r among sisters often below 0.75 (multiple mating, multiple queens) reproductive value, sex ratios B can be very large

r between sisters = 0.75 r between brothers & sisters = 0.25 For workers 3:1 sex ratio is optimal r between mothers & daughters = 0.5 r between mothers & sons = 0.5 For queens, 1:1 sex ratio is optimal. Conflict between workers & queens over the optimal sex ratio. Kin selection can also cause conflict within colonies

Sex ratio skew Is the ratio 1:3 or 1:1? (are workers in control, or are queens?) 1. Because males are haploid, queens control the primary sex ratio. 2. Because workers rear the young, they control the secondary sex ratio.

Sex ratio skew Ratios are female-biased in single-queen ant colonies. No relatedness asymmetry = less sex ratio bias: multiple-queen ant colonies (low r) solitary bees & wasps (only primary sex ratio) termites (diploid)

Sex ratio skew Within-species variation also matches expected patterns. Queller & Strassmann 1998

How direct altruism toward relatives? Many transitions were promoted by mechanisms that isolate particular groups.

Social Insect Recognition Systems Label Template AB EF AE

Label Template AB EF AE A B A B Social Insect Recognition Systems

Problem: imprinting decouples template from kinship. In cross-fostering experiments, callows imprint on the wrong odors. In some cases, things can go really awry…

Cal. Acad. Sci. When recognition systems break down: Polyergus breviceps Specialized mandibles: cannot hunt, eat, etc.

Polyergus breviceps; Alex Wild When recognition systems break down:

Many forms of social parasitism within ant colonies: reproductive skew slavemaking inquilinism cuckoos When recognition systems break down: