L17 application of inclusive fitness examples

Question 1

What is Hamilton’s rule?

Answer 1

R × b – c > 0, where R = relatedness, b = benefit to recipient’s reproduction, c = cost to actor’s reproduction.

Question 2

How is Hamilton’s rule expanded for multiple recipients?

Answer 2

Σ(Rᵢ × bᵢ) – C > 0, summing each recipient’s relatedness × benefit minus total cost.

Question 3

How does Hamilton’s rule handle mixed helping and harming?

Answer 3

Sum of (R × b) terms minus sum of (R × c) terms > 0, or R₁B – r₂C > 0 when comparing helping vs direct reproduction.

Question 4

According to Hamilton’s rule, toward whom should cooperative behaviours be directed?

Answer 4

Closer relatives (higher R values).

Question 5

According to Hamilton’s rule, toward whom should harming behaviours be directed?

Answer 5

Away from close kin (lower or negative R impact).

Question 6

What is kin discrimination?

Answer 6

The ability to direct behaviours based on recognition of relatives versus non-relatives.

Question 7

What are the two main kin recognition mechanisms?

Answer 7

Genetic cues (e.g., specific alleles or green-beard genes) and environmental cues (e.g., familiarity, shared nest or song dialect).

Question 8

In long-tailed tits, what choice do helpers make and why?

Answer 8

Failed breeders choose to help nests of kin—identified by song similarity—regardless of distance.

Question 9

What mechanism underlies kin discrimination in long-tailed tits?

Answer 9

Environmental cue: chicks learn natal song; helpers use song similarity to recognize kin.

Question 10

Describe the life‐cycle altruism in social amoebae (slime mould).

Answer 10

Under starvation, ~100,000 cells aggregate → migratory slug → fruiting body; ~20% sacrifice to form non-reproductive stalk, elevating kin spores.

Question 11

Which genes enable kin discrimination in slime mould and how?

Answer 11

tgrB1 and tgrC1 encode matching transmembrane proteins—a green‐beard system ensuring cooperation only with identical alleles.

Question 12

What did field samples of natural fruiting bodies reveal about slime mould relatedness?

Answer 12

Fruiting bodies are nearly clonal, showing high relatedness among cooperating cells.

Question 13

What are the two larval morphs of tiger salamanders and their behaviours?

Answer 13

Wild‐type larvae (normal head) and cannibal morph (wide head, sharp teeth) that preys on conspecifics.

Question 14

How does relatedness influence the emergence of the cannibal morph in tiger salamanders?

Answer 14

Cannibal morphs appear more in low‐related (mixed‐family) groups and preferentially prey on cousins over full siblings.

Question 15

What key prediction of Hamilton’s rule does the tiger salamander study illustrate?

Answer 15

Harmful behaviour (cannibalism) is directed away from closest kin.

Question 16

List the four critical empirical examples of kin discrimination covered.

Answer 16

Long-tailed tits (song-based helping), social amoeba (tgr genes in fruiting bodies), tiger salamanders (kin‐dependent cannibalism), plus broad concept of kin discrimination.

Question 17

What is the empirical goal when testing Hamilton’s rule in nature?

Answer 17

To measure R, b, and c in wild populations and test if R × b – c > 0 predicts cooperation.

Question 18

In empirical tests of Hamilton’s rule, what two fitness‐maximizing options are compared?

Answer 18

Helping another brood (inclusive fitness = R × b) versus not helping (direct fitness = r₀ × c₀).

Question 19

In long‐tailed tits, what is the benefit (b) each helper provides to a focal chick?

Answer 19

Each helper increases a chick’s chance of recruiting next year by 0.29.

Question 20

What is the average relatedness (R) between helpers and breeders in the long‐tailed tit study?

Answer 20

R = 0.16 (slightly closer than cousins).

Question 21

How is the cost component (c × r₀) quantified in the long‐tailed tit test?

Answer 21

Helping reduces the helper’s own survival, amounting to a 0.48 genetic‐equivalent loss.

Question 22

What conclusion did the long‐tailed tit study reach regarding Hamilton’s rule?

Answer 22

Despite R × b (0.16×0.29) being less than 0.48, helpers gain net inclusive fitness by assisting, so Hamilton’s rule is satisfied.

Question 23

Which other taxa have had parameter‐estimation studies confirming R × b exceeds c × r₀?

Answer 23

Bees, wasps, various bugs, turkeys, and tiger salamanders.

Question 24

What cooperative trait do some mammalian viruses express?

Answer 24

Secretion of interferon‐blocking proteins that protect neighboring virions.

Question 25

What are the measured cost (c) and benefit (b) for viral interferon‐blockers?

Answer 25

Cost = 0.4 growth reduction for the producer; benefit = 1.6 growth boost for neighbors.

Question 26

How is the critical relatedness threshold (R*) for viral cooperation calculated?

Answer 26

R* = c / b = 0.4 / 1.6 = 0.25.

Question 27

Why does interferon‐blocking evolve by kin selection in viruses?

Answer 27

Because viral inocula are largely clonal (R >> 0.25), satisfying Hamilton’s rule.

Question 28

What’s the difference between conditional and fixed cooperation strategies?

Answer 28

Conditional: help chosen case‐by‐case; Fixed: strategy set early and maintained for life.

Question 29

What does Hamilton’s rule predict about fixed cooperative traits?

Answer 29

They evolve tuned to the average relatedness experienced in the species’ evolutionary history.

Question 30

How do “staying together” versus “aggregation” group formations differ?

Answer 30

Staying together yields high relatedness (R) and more cooperation; aggregation yields low R and less cooperation.

Question 31

What did Fisher (2013) find regarding staying‐together vs aggregative microbes?

Answer 31

Clonal (“staying together”) species show more division of labour and sterile cells; aggregative species show less altruistic specialization.

Question 32

According to Downing (2020), how do family‐based vs aggregative bird cooperators differ in shared paternity?

Answer 32

Family‐based cooperators have lower shared paternity (more helpers per breeder) than aggregative cooperators.

Question 33

How does a mating system serve as a proxy for relatedness in groups?

Answer 33

Monogamy (single mating) yields high relatedness among nestmates; polyandry (multiple mating) yields lower relatedness (half- or quarter-siblings).

Question 34

What prediction follows from monogamy versus promiscuity regarding cooperation?

Answer 34

Species with ancestral monogamy should evolve more cooperation than species with promiscuous mating.

Question 35

In eusocial insects under monogamy, why might a worker help raise siblings instead of reproducing?

Answer 35

Full siblings have r = 0.5, equal to r₀ ≈ 0.5 for own offspring, so helping yields inclusive fitness benefits.

Question 36

How does multiple mating change siblings’ relatedness and affect worker decisions?

Answer 36

Multiple mating produces half- or step-siblings (r < 0.5), making direct reproduction (r₀ = 0.5) more favorable than helping.

Question 37

Which avian species illustrate variation in extra-pair paternity and cooperative breeding?

Answer 37

Seychelles warbler (facultative helpers), white-winged choughs (obligate helpers), puffins (low EPP, no helpers), superb fairy wrens (high EPP, but cooperative).

Question 38

What did the meta-analysis of birds find about promiscuity and cooperative breeding?

Answer 38

Cooperative breeders have significantly lower extra-pair paternity rates than non-cooperative breeders.

Question 39

Within cooperative bird species, how does extra-pair paternity affect helper occurrence?

Answer 39

The proportion of nests with helpers declines as extra-pair paternity rises.

Question 40

What does phylogenetic reconstruction reveal about monogamy and cooperative breeding?

Answer 40

Evolutionary transitions to monogamy typically precede the origin of cooperative breeding.

Question 41

In which lineages is true eusociality found only when ancestry is monogamous?

Answer 41

Eusocial shrimps, bees, and ants all evolved sterile castes in ancestrally monogamous lineages.

Question 42

What did Griffin (2004) demonstrate about β-lactamase secretion in bacteria?

Answer 42

In high-R populations (single-clone founders), cooperators fix over generations; in low-R (mixed founders), cooperators go extinct.

Question 43

How do microbial public-goods experiments support Hamilton’s rule?

Answer 43

They show that higher relatedness favors the maintenance of costly cooperative traits, while low relatedness leads to collapse of cooperation.

Question 44

How can population genetics reveal signatures of cooperation?

Answer 44

By comparing nucleotide diversity: cooperative-gene loci show elevated polymorphism and weaker fixation of beneficial mutations than private-gene loci.

Question 45

Why are cooperative genes under weaker selection than private genes?

Answer 45

Because benefits accrue to relatives (diluted benefit to the producer), making it harder for cooperative alleles to fix.

Question 46

How can a high benefit-to-cost (b/c) ratio drive cooperation at low relatedness?

Answer 46

When b/c is large, the net gain (b − c) can favor cooperation even if R is near zero.

Question 47

Give an example of cooperation evolving at low relatedness due to high b/c.

Answer 47

Algae form non-kin aggregates to avoid predation because the survival benefit outweighs the low relatedness cost.

Question 48

What types of cooperation can evolve without kinship?

Answer 48

Mutualisms (between species) and low-cost behaviours (e.g., grooming in primates).

Question 49

Beyond cooperation, what else does inclusive fitness theory predict?

Answer 49

Sex-ratio biases (e.g., fig wasp clutches), worker-policing, and other social traits driven by relatedness.