21 - Social + Kin Selection

What is social behavior in evolutionary terms?

Interactions between individuals that affect fitness of actor and recipient.

What are the 4 types of social behavior?

Selfishness, mutual benefit, altruism, spite.

What is selfishness?

Actor benefits, recipient is harmed.

What is mutual benefit?

Both actor and recipient benefit.

What is altruism?

Actor is harmed, recipient benefits.

What is spite?

Both actor and recipient are harmed.

Concept: What determines type of social behavior?

The fitness effects on actor and recipient (+ or -).

Example: What is tadpole cannibalism?

A selfish behavior benefiting the actor and harming the recipient.

Concept: Why is cannibalism favored?

Increases nutrition and reduces competition.

What is spite in bacteria?

Releasing toxins that harm others at a cost to self.

Concept: When can spite evolve?

When it harms less-related individuals more than relatives.

What is mutual benefit in groups?

Cooperation that increases survival for all individuals.

Example: Why do birds nest in groups?

Better defense against predators.

Concept: Why is group living beneficial?

Reduces individual risk.

What is altruism?

Behavior that reduces actor fitness but increases recipient fitness.

Example: Why do mongooses help raise others’ young?

Because they are related (kin selection).

What is inclusive fitness?

Total fitness including direct and indirect fitness.

What is direct fitness?

Personal reproduction and survival.

What is indirect fitness?

Fitness gained by helping relatives reproduce.

What is kin selection?

Natural selection favoring traits that increase indirect fitness.

What is Hamilton’s Rule?

Br > C.

What does B represent?

Benefit to recipient.

What does C represent?

Cost to actor.

What does r represent?

Relatedness.

Concept: When is altruism favored?

When Br > C.

Concept: What does relatedness measure?

Probability of shared genes by descent.

What is relatedness for full siblings?

0.5.

What is relatedness for half siblings?

0.25.

What is relatedness for cousins?

0.125.

Concept: Why does relatedness matter?

Higher relatedness increases likelihood of altruism.

Example: What is siblicide?

Killing siblings when cost outweighs benefit.

Concept: When does siblicide occur?

When Br < C.

Example: Which birds show siblicide?

Masked boobies.

Concept: Why do parents allow siblicide?

Maximizes survival of strongest offspring.

What is kin-directed altruism?

Helping relatives more than non-relatives.

Example: What do prairie dogs do?

Give alarm calls more often when kin are nearby.

Concept: Why alarm calls are costly?

Increase risk to caller.

Concept: Why still evolve?

Protects relatives carrying shared genes.

What happens when prairie dogs change groups?

Alarm calling behavior changes with relatedness.

Concept: What does this show?

Behavior is flexible based on kin presence.

What is adoption in red squirrels?

Caring for non-biological offspring.

Concept: When is adoption favored?

When Br > C.

Concept: Who do squirrels help?

Relatives rather than unrelated individuals.

What is cooperative breeding?

Individuals help raise offspring that are not their own.

Example: What birds show cooperative breeding?

White-fronted bee-eaters.

Concept: Why help instead of reproducing?

Indirect fitness gains.

Concept: What affects cooperative breeding?

Level of relatedness.

Concept: How does promiscuity affect cooperation?

Reduces relatedness, lowers cooperation.

Concept: Why does low relatedness reduce helping?

Lower indirect fitness benefits.

What is parent-offspring conflict?

Conflict over resource allocation.

Concept: Why does conflict occur?

Parents and offspring have different fitness interests.

What is weaning conflict?

Disagreement over when to stop parental care.

Concept: Why do offspring want more care?

They benefit directly.

Concept: Why do parents limit care?

To conserve resources for future offspring.

Concept: What is optimal care for parents?

Maximizes total reproductive success.

Concept: What is optimal care for offspring?

Maximizes individual survival.

What is effect of half-siblings?

Lower relatedness increases conflict.

Concept: Why does extrapair mating increase conflict?

Creates half-siblings with lower relatedness.

What is eusociality?

Extreme form of social behavior with non-reproductive individuals.

What is facultative eusociality?

Individuals help only under certain conditions.

What is true eusociality?

Individuals help and never reproduce.

What are key features of eusociality?

Overlapping generations, cooperative care, non-reproductive castes.

What is haplodiploidy?

Sex determination system in some insects.

Concept: What is relatedness between sisters in haplodiploidy?

0.75.

Concept: Why does haplodiploidy promote altruism?

Sisters share more genes than with offspring.

Concept: Is haplodiploidy required for eusociality?

No, but it can facilitate it.

What are key factors promoting eusociality?

Nest building, extended care, cooperation, relatedness.

Example: What organisms show eusociality?

Ants, bees, naked mole rats.

Concept: Why do eusocial individuals not reproduce?

They gain indirect fitness.

Concept: What is overall takeaway of kin selection?

Genes promoting helping relatives can spread.