Lec 13 Flashcards
Natural selection favors ANY gene copies that maximize the fitness of the individual
There is NO goal to natural selection and adaptation
there is NO doing things for the good of the species
Evolution acts on the INDVIDUAL
Evolution is just a generation–by-generation response to prevailing ecological conditions
Cooperation
Occurs when 2 individuals receive a net benefit from their joint interactions
Problems with the evolution of cooperation by natural selection
How can altruism (the sacrifice of one’s own fitness for the benefit of another individual’s fitness) evolve?
-Individuals should never sacrifice their own fitness
What about cheaters?
What is fitness at the genetic level?
Leaving as many copies of your genes in the next generation, regardless of who has them
Passing on genes to the next generation
A broader definition of tiness
Inclusive fitness
An organisms’ own survival and reproduction plus the survival and reproduction of individuals with whom the organism shares genes
Kin selection and inclusive fitness
Inclusive fitness = sum of direct and indirect fitness
Direct fitness = component of fitness gained from producing offspring
Indirect fitness = component of fitness gained by aiding related individuals
Kin selection = process by which characteristics are favored due to their effects on relatives
The coefficient of relatedness
The probability that an allele in one individual has a copy that is identical by descent in the other individual
If you help your relatives increase their fitness, is that altruism?
It depends on how much you help vs. how related you are
Hamilton’s rule
Altruism favored when relatedness benefit is greater than cost of a particular behavior
When does “altruism” happen under Hamilton’s rule?
Benefits outweigh costs when a gene increases in frewuncy regardless of who carries that gene
Imagine an action that kills the actor to save the recipients. The action should occur if it saves 2 siblings/offspring, 4 grandparents, 8 cousins, etc
Alarm calls
Seem altruistic - warns others of predators
ALarm calls only when around relatives
Alarm call only when costs are low
Still may be some “direct benefits” of alarm calling that we don’t udnerstand
You observe that male wild turkeys often form coalitions, where 2 males will cooperatively court a female. However, only the more dominant of the 2 males ever seems to mate. Why might the subordinate turkey still help with courtship?
He is related to the dominant male and he gets more fitness by helping his relative mate than if he tried to court females on his own
Eusocial insects and inclusive fitness
Eusociality involved division of reproductive labor, cooperative rearing of young, and overlapping generations
Evolved independently in several insect species, shrimps, and naked mole rats
Most often associated with hymenopterans (ants, bees, and wasps)
Eusoaicality and haplodiploidy
Eusociatily may occur in part becauwe of haplodiploidy
All males are haploig, and all females are diploid
Thsi means that full sisters have a relatedness coefficient of 0.75 - closer than their own offspring
by helping their mother produce more workers, they perpetuate more of thier genes than if they reproduced themselves
Problems with the evolution of cooperation by natural selection
How can altruism evolve?
-Individuals should never sacrifice their own fitness
If you are related to the individuals you are helping, it’s NOT true altruism - your genes will still benefit
What about cheaters?
What should you do in Prisoner’s Dilemma?
Testify against your partner (defect)
What should you do if you know what your partner will do?
Defect no matter what
If it always pays to defect, then cooperation will not be evolutionarily stable
When we observe cooperation in nature, we need to figure out the payoff matrix that favors cooperation
Evolutionarily stable strategies
Definition: A strategy that, if adopted by all members of a population, cannot be halted by an alternative strategy
In other words: We want to find an approach that cannot be invaded by another approach
Cooperation is highly susceptible to cheating - when we observe cooperation evolving, it must be because the benefits of cooperating outweigh the costs of cheating
Altruism via reciprocity
Suffer a cost now for the promise of future paybakc
When could reciprocity evolve?
When you are certain that you wi.l interact with theother individuals in the future and there is a way for you to get payback if they cheat
Reciprocity can evolve when:
There are many repeated pairwise interactions (individuals live together for a long time)
Individuals help others to the extent they have helped them previously - must be able to recognize cooperators and cheats and withhold future help from cheaters
HARD to evolve - can often be more easily explained by individuals acting for their own benefit
Reciprocity among nonkin
Vampire bats roost during day
Adults forage at night
Some return w/o eating
Bats exchang eblood meals more often with those they interact with more
How can cooperation evolve?
Kin:
-Kin selection
Non-kin:
Reciprocity (or kin)
By-produce mutualisms
Enforcement
By product mutualism
Cooperation arises due to individual benefits, benefit to others is a by-product
Birds chasing away hawks from their own nests; do not chase to get away from other’ nests
Game theory model:
- If everyone hunts, everyone gets food
- If one doesnt hunt, there is less food
- If 2 dont hunt, everyone hungry
- If no one hunts, everyone suffers
Hunting together is always the best strategy
Are individuals in a by-product mutualism behaving altruistically?
No they are acting selfishly but cooperating is the strategy that most increases their fitness
Cooperation among non-kin: enforcement
A mechaism that PUNISHES CHEATERS (instead of rewarding cooperators) could also favor cooperation
Adding enforcement to the Punisher’s Dilemma can lead to stability
Enforcement examples:
- Eviction
- Infanticide
- Punishment
- Sanctions
- Reciprocity
I.e. cleaner fish and clients; cleaner fish may try to bite flesh, clients back away from cleaner then charge = cleaner just eats pests
4 hypotheses for evolution of cooperation
Kin selection
Reciprocity
By product benefits
Enforcement
For cooperation to evolve, you need:
1) Greater individual benefit to cooperative behavior than cost
2) Can have inclusive fitness benefits (which are hard to measure)
The evolution of sociality provokes conflict
Most scial behaviors are conflict based
Conflice can occur over:
- Food
- Mates
- Parental care
Conflict occurs BETWEEN: -Parents and offspring -Males and females _predators and prey -Parasites and hosts -Individuals with similar resource requirements
Why might there be a conflict of interest between parents and offspring?
a) Offspring want parents to invest more resources int hem than is optimal for their parents
b_ Parents must strategically allocate resources to current vs. future offspring
c) All offpsring are equally valuable to a parent, but each individual offspring values itself more than its parents or siblings
d) All of the above
d) All of the above
Evolution of parental care
Different taxonomic groups vary in how much parental care they provide
Combination of physiology and ecology determines amount of parental care given in a particular group
Birds: Both sexes benefit (double fitness) when they both care. When food is very abundant, the male may desert
Mammals: Females invest even more in offspring due to internal gestation and lactation. Males can then easily desert
Fish: Care is simple: involves protecting or fanning eggs and be done be one sex. usually males in external fertilizers and females in internal fertilizers
Parent-offspring conflict
Inclusive fitness theory predicts that parents should go to great lengths to help their offspring because on average, they have an r = 0.50
Parent-offspring conflict arises when parents must decide how much aid to give to any particular offspring
How much to care?
Parents have only a finite amount of resources to allocate to offspring care over their lifetimes
How should they spread those resources among offspring?
2 stages of tradeoffs:
1) Within brood: Do you have a small or large brood?
2) 0 Current vs. future broods: Do you invest all your resources in currect reproduction, or save some for the future
Conflict arises between parent and offspring because offspring will always want more resources from parents than parents will “want” to give them
Intra-brood:
Each offspring should demand more than its fair share
Inter-brood:
Current broods should demand more, at the expense of future broods
