Lecture # 12 | Cooperation and Conflict

Conflict

When the fitness interests of two individuals are different

Cooperative

When one individuals’s behaviors benefits another

Selfish

+ effect on actor

- effect on recipient

Spiteful

- effect on recipient

- effect on actor

Mutalistic

+effect on actor

+effect on recipient

Altruistic

-effect on actor

+effect on recipient

Cheaters

Individuals that benefit from the action of others without providing benefits to them in return

What occurs if a cheater has high fitness in a population of cooperators?

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

ex: slime mold evolution under lab conditions

Why do individuals exhibit traits that increase the fitness of other individuals (rather than focusing all of their energy on improving their own fitness) ?

1. Group selection

2. Direct benefits (byproducts)

3. Reciprocity

4. Kin selection

Group selection

Variation in reproduction success among groups

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

• relatively rare

Direct Benefits (byproduct)

Individuals help others because they ultimately gain direct benefit from their cooperative behavior

1. Initial action is a selfish one, but cooperation is a byproduct

ex: cooperation in herds to protect from individual predation

Reciprocity

Individuals take on a cost to benefit Y, and Y in turn reciprocates that benefit to X

ex: vampire bats rely on giving to one another in hope they will be helped in need

Prisoner’s dilemma

A model to predict the conditions under which reciprocity is favored

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

• Repeated interactions can favor cooperative behavior

  

Altruism

Cooperation with no direct benefit for the cooperator

• ex: sterile worker bees help others in the hive and do not breed themselves

Kin selection

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

• unlike other forms of cooperation, kin selection can only evolve among members of the same species

• inclusive fitness

• logic is formalized in Hamilton’s rule

Direct fitness

The fitness of an allele that included its positive effect on the bear of that allele

Indirect fitness

The positive effect on related individuals that also share the same alleles

Inclusive fitness

The combination of both direct fitness and indirect fitness

Hamilton’s rule

An allele that causes an altruistic behavior will spread if the following condition is met

• rB>C

  • r= relatedness

  • B= fitness benefit to the recipient

  • C= the fitness cost to the actor

Inclusive fitness of an allele

rB-C

How to calculate relatedness

1. Find the common ancestor

2. Count the generations

3. Apply the formula r= (1/2)^n, where n is the number of generations between the two individuals

4. Account for shared family members and multiple by 0.5

How related are first cousins?

1. Common ancestors are grandparents

2. 2 generations between first cousins through common grandparents

3. 1/2²= ¼

4. Account for shared grandparents by multiplying by 0.5

5. Related by 1/8

Conditions needed for spiteful alleles to spread

• The 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

In systems with haplodiploidy, what is r between a sister and a brother

0.25, as the brother shares 100% of his genes with his mother and none of the father

• share 50% of their mothers genes and 0% of their fathers

In a system with haploiddiploidy, what is the relatedness between two sisters

0.75, as their share 100% of their fathers and 50% of their mothers

Sexually antagonistic selection

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

• Traits like:

  • Mating frequency

  • Parental car

How is mating frequency a sexually antagonistic trait?

Males often benefit from mating when females dont

How is parental care a sexually antagonistic trait?

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

Infanticide

Killing the young of its own species

• sometimes an individuals fitness is enhance by killing the young of its own species

• Male infanticide is common in mammals

Examples of infanticide

1. Male lions that take over a pride will kill all the infants in the pride to speed up the time to sexual receptivity in the females of the pride

2. Female mice will kill some of their young when resources are scare to save energy for reproduction

Parent-offspring conflict

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

• selection favors offspring that take more resources from their parents, even if that decreases the number of other offspring they have

• as direct fitness is gained → indirect fitness is lost

• Human embryos have evolved to extract more resources from mothers than mothers are favored to give

Is natural selection always at the individual level and above?

No, there can be conflict at the genetic level → genic selection

• selfish DNA can spread in populations even if it decreases survival or reproduction

Segregation distorters

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

• an example of selfish DNA that can spread in populations

Transposable elements

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

• an example of selfish DNA that can spread in populations

Cytoplasmic male sterility

When a mutation inherited through the cytoplasm causes sterility

• an example of selfish DNA that can spread in populations