1. 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

2. 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.

3. 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?

4. 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

5. Alarm Calls: Beldings Ground Squirrels
Paul Sherman
Beldings Ground Squirrel

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

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

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

9. Altruistic behavior is not dispensed randomly

10. 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

11. 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).

12. 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.

13. 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.

14. More likely to share because of degree of association

15. And because of degree of relatedness

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