Lecture 12: Cooperation and Conflict

interaction types are defined by what

the fitness effect on each partner

when the fitness interests of two individuals are different, they are in ___

conflict

when one individual’s behavior benefits another, the behavior is ___

cooperative

cheaters

benefit from the actions of others without providing benefits to them in return

if a cheater has high fitness in a population of cooperators, then…

a mutation that causes individuals to cheat will spread, and cooperation can collapse

why do individuals exhibit traits that increase the fitness of other individuals?

1. group selection

2. direct benefits (byproducts)

3. reciprocity

4. kin selection

group selection

• variation in reproductive success among groups

• group selected traits are beneficial to the groups that bear them

direct benefits (byproducts)

• individuals help others because they gain direct benefit from their cooperative behavior

• cooperation is a byproduct of selfish action

reciprocity

• individual X takes on a cost to benefit Y, and Y reciprocates that benefit to X

prisoner’s dilemma

each of 2 individuals will do best by acting selfishly, but if both of them act selfishly, they will do worse than if they both cooperate

selfish behavior is favored if what?

if individuals interact only once

cooperative behavior is favored if what?

if individuals have repeated interactions

altruism

cooperation with no direct benefit for the cooperator

kin selection

selection on alleles that promote cooperative behavior with other individuals that share the same alleles (identical by descent)

inclusive fitness of an allele includes what?

• its positive effect on the bearer of that allele (direct fitness)

• the positive effect on related individuals that also share the same allele (indirect fitness)

kin selection can only evolve among ..?

members of the same species

hamilton’s rule

an allele that causes an altruistic behavior will spread if the following condition is met: rB>C

r in rB>C

the relatedness ( when the allele is rare, r is the probability that the recipient of altruistic behavior also carries the allele)

B in rB>C

the fitness benefit to the recipient

C in rB>C

the fitness cost to the actor

rB - C

stands for inclusive fitness of an allele

how to calculate relatedness

• For the autosomes of a diploid species, the alleles in a mother are related to those in her offspring, with r = 0.5

• The alleles in a given daughter are also related to those in her brothers and sisters, with r = 0.5.

inclusive fitness explains the evolution of ___ traits

spiteful

a behavior is spiteful if what?

if it harms both the actor and the recipient

conditions needed for spiteful alleles to spread:

• actor be less closely related to the recipient than to an average member of the population

• harming the recipient enhances the fitness of other individuals in the population that are more closely related to the actor

eusociality

when some individuals do not reproduce and instead rear the offspring of others

sex determination is incredibly ___

variable

sexually antagonistic selection

when a trait that is favored to increase in one sex is favored to decrease in the other

sexually antagonistic selection examples

• Mating frequency

  • Males often benefit from mating when females don’t

• Parental care

  • Selection favors offspring abandonment in the parent that pays the greater cost

infanticide

an individual’s fitness in enhanced by killing the young of its own species

Parent-offspring conflict

When what is best for a parent conflicts with what is best for an offspring

Offspring can gain indirect fitness by helping their siblings but often have even more to gain by …

increasing their own survival

Selection favors ____, even if that decreases the number of other offspring they have, so long as direct fitness gain > indirect fitness loss

offspring that take more resources from their parents

Inclusive fitness favors what?

parents that maximize the number of offspring they have, not divert extra resources to selfish ones

Natural selection can occur at different levels of biological organization

1. Genic selection

2. Individual selection

3. Group or interdemic selection

4. Species or lineage selection

Segregation distorters

mutations that cause an allele to have a greater than 50% chance of inheritance

Transposable elements

short sequences of DNA that are able to insert additional copies of themselves in the genome

Cytoplasmic male sterility

when a mutation inherited through the cytoplasm causes sterility