Kin Selection Flashcards
Altruism
An action that reduces an
individual’s own fitness while
increasing the fitness of another individual.
Altruism is evolutionarily unstable.
But behavior that benefits the
group (or others in the group)
is widespread.
Nash equilibrium
a strategy that is the best response, given other participant’s responses.
No-one benefits further unless
multiple participants agree to change their strategies.
Evolutionarily Stable Strategy (ESS)
a strategy that, if established, cannot be invaded by a rare mutant using an alternative strategy.
*a special-case of Nash equilibrium.
Altruism is unstable
Behavior that benefits the
group (or others in the group)
is widespread
Cooperatively
breeding
organisms
Some members forego reproduction while in the group.
May risk death by defending
the colony.
Devote energies toward rearing of young of others (helping at the nest.)
Examples: Meerkats, wolves:
Kin selection and alarm calling.
Species are eusocial if:
Individuals cooperate in the care of young. There is reproductive division of labor, with sterile (or nearly sterile) workers assisting fecund individuals.
How can this seemingly
altruistic behavior be explained?
The evolution of altruism requires:
Heritable variation in altruism.
Positive association between altruists.
Selection at the level of the family (kin selection).
Reciprocity
Kin selection (Hamilton 1963)
Selection acting on individuals related through recent, common descent.
Depends on relatedness, “r”, the probability that two individuals share a particular allele. Group members are more similar to one another than to members of other groups.
Altruism can evolve among relatives because altruism will benefit other altruists (thus a Positive association between altruists).
Adaptations that benefit the group at the expense of the
individual
– groups composed of relatives
some caveats:
– Grouping with kin does not necessarily mean cooperation
Members of some cooperative groups are little or no more related than random.
Calculating Relatedness
– diploid case
(A) has two sets of chromosomes, one from
mother and one from father.
Chance of picking mother’s copy is 1/2.
Chance mother gave it to (B) is also 1/2.
So, through mother (1/2)(1/2) = (1/4).
Chance of picking father’s copy is 1/2.
Chance father gave it to B is also 1/2.
So, through father (1/2)(1/2) = (1/4).
Diploid Case (everyone is 2N)
Combined probability is mother + father
1/4mother + 1/4father = 1/2
(A) and (B) are related symmetrically by 1/2.
Hamilton’s Rule & Fitness
Hamilton 1963
Fitness = direct fitness + {(r) x fitness effect on relatives}
Fitness =
direct fitness + indirect fitness
INCLUSIVE FITNESS
Hamilton’s Rule
c = cost to altruist b = benefit to altruist's relatives
fitness if selfish = w
fitness if altruist = w - c + (r)(b)
act altruistically if fitness of altruist > fitness if selfish:
(c) < (r) x (b)
Eusocial insects
Many eusocial insects are haplodiploid.
Hymenoptera: bees, ants and wasps.
Thysanoptera: gall-forming thrips
Coleoptera: ambrosia beetles
Other eusocial insects mostly reproduce clonally.
Hemiptera: gall-forming aphids
Does high relatedness / relatedness asymmetry explain eusociality?
Haplodiploidy
Example: Bees
Females develop from fertilized eggs
Diploid (2N)
Males develop from unfertilized eggs
Haploid (N)
Reciprocal altruism
Altruism is rewarded with altruism, defection punished by defection.
Defectors are ‘punished’ because they do not receive cooperation in the future.
Vampire bats (Wilkinson 1984)
Groups of 8-12 females and their offspring.
r = 0.11
Share blood meal by regurgitation.
33% juveniles and 7% of adults fail to feed each night.
Starvation if not fed in 3 nights.
