Types of Social Interactions

The actor in any social interaction affects the recipient of theaction as well as itself. The costs and benefits of interactionsare measured in units of surviving offspring (fitness)

Actor: Benefits Harmed

Benefits Cooperative AltruisticRecipient:

Harmed Selfish Spiteful

Kin selection: When natural selection favorsthe spread of alleles that increase the indirectcomponent of fitness.

Direct Fitness: an individual’s reproductive potential.

Indirect Fitness: additional reproductive potential made possible by an individual’s actions.

The Two Components of Inclusive Fitness

Coefficients of Relatedness

What is the probability that alleles are identical by descent?

The coefficient of relatedness (r) between two individuals is defined as the percentage of genes that those two individuals share by common descent.

An allele for alturistic behaviorwill spread if:

Br - C > 0

Benefit to recipient Cost to actor

Hamilton’s Rule

How many cousins must an actor indirectly help to obtain a roughly equivalent inclusive fitness?

Beldings Ground Squirrel

Alarm Calls: Beldings Ground SquirrelsPaul Sherman

Females are more likely to call when close relatives are within earshot

Closely related kin are more likely to cooperate in chasing away trespassing ground squirrels

White-fronted bee-eater Merops bullockoides

Colonies of 40-450 Subdivided into Clans of 3-17

0.47 additionaloffspring per nestbecause of helping

Steve Emlen

Altruistic behavior is not dispensed randomly

Evolution of Eusociality

1) Overlap in generations between parents and their offspring2) Cooperative brood care3) Specialized castes of nonreproductive individuals

Variety of insects, snapping shrimp, mole rats

Haplodiploidy And

Eusocial Hymenoptera

Prob homologous alleles are IBD between hymenopteran sisters:

r = (1 x 1/2) + (1/2 x 1/2) = 3/4

Prob homologous alleles are IBD between mother and daughter:

r = 1/2

This system favors the production of reproductive sisters over daughters, sons or brothers.

Females should maximize their inclusive fitness by investing in the production of sisters (by acting as workers and not reproductives).

Rationale for the Haplodiploidy Hypothesis

Does the Haplodiploidy Hypothesis Explain Eucociality?

Molecular marker studies (Avis Chapter 6) show that genetic relatedness is often lower than 3/4 among workers.

a) multiple, unrelated queens have been identified in colonies(polygyne not monogyne)(Table 6.2)

b) queens (reproductives) may mate with multiple males.

Vampire Bats: Gerald Wilkinson

Desmodus rotundus

Need blood meal often (within 1-3 days)

Bats roost in groups of 8-12 females and their children.

Groups often mix during the day, flying from tree to tree.

Individuals may share blood meal because of association and / or genetic relatedness.

More likely to share because of degree of association

And because of degree of relatedness

Anthias squamipinnis

Do kin maintain contactthroughout the Pelagicphase of life?

serranid reef fish