Types of Social Interactions The actor in any social interaction affects the recipient of the action as well as itself. The costs and benefits of interactions are measured in units of surviving offspring (fitness) Actor: Benefits Harmed Benefits Cooperative Altruistic Recipient: Harmed Selfish Spiteful

The Two Components of Inclusive Fitness Direct Fitness: an individual’s reproductive potential. Indirect Fitness: additional reproductive potential made possible by an individual’s actions. Kin selection: When natural selection favors the spread of alleles that increase the indirect component of fitness.

Coefficients of Relatedness The coefficient of relatedness (r) between two individuals is defined as the percentage of genes that those two individuals share by common descent. What is the probability that alleles are identical by descent?

How many cousins must an actor indirectly help to obtain a roughly equivalent inclusive fitness? Hamilton’s Rule An allele for alturistic behavior will spread if: Br - C > 0 Benefit to recipient Cost to actor

Alarm Calls: Beldings Ground Squirrels Paul Sherman Beldings Ground Squirrel

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

Subdivided into Clans of 3-17 Colonies of 40-450 Subdivided into Clans of 3-17 0.47 additional offspring per nest because of helping White-fronted bee-eater Merops bullockoides Steve Emlen

Altruistic behavior is not dispensed randomly

Evolution of Eusociality Overlap in generations between parents and their offspring Cooperative brood care Specialized castes of nonreproductive individuals Variety of insects, snapping shrimp, mole rats Haplodiploidy And Eusocial Hymenoptera

Rationale for the Haplodiploidy Hypothesis 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).

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

Do kin maintain contact throughout the Pelagic phase of life? serranid reef fish Anthias squamipinnis