L15 Kinship

📘 DETAILED MULTIPARAGRAPH SUMMARY

Kinship and Altruistic Behaviour
In animal behaviour, kinship plays a crucial role in shaping social interactions. One of the key puzzles biologists study is why an individual would perform apparently self-sacrificial acts, such as giving alarm calls that attract predators to itself. The answer lies in genetic relatedness: individuals may behave altruistically if such actions enhance the survival of their genetic relatives, thereby indirectly promoting the transmission of their own genes. This is known as inclusive fitness theory, introduced by W.D. Hamilton.

Belding’s Ground Squirrel and Kin Selection
Belding’s ground squirrels offer a classic example of kin-selected altruism. In these mammals, alarm calls are primarily made by females rather than males. This pattern arises because males typically disperse from their natal area to find mates, while females remain in their birthplace, surrounded by relatives such as mothers, daughters, and sisters. By emitting alarm calls, females help protect kin, thereby improving their inclusive fitness even if they incur personal risk. This behaviour illustrates Hamilton’s rule: altruistic behaviour is favoured when the genetic relatedness (r) multiplied by the benefit to the recipient (B) exceeds the cost to the actor (C).

Inclusive Fitness and Hamilton’s Rule
Inclusive fitness includes both direct fitness (the number of one’s own surviving offspring) and indirect fitness (the contribution to the reproductive success of genetic relatives). Genetic relatedness (r) measures the probability that two individuals share alleles identical by descent. For example, siblings share r = 0.5, grandparents and grandchildren r = 0.25, and cousins r = 0.125. Hamilton’s rule (rB > C) predicts that natural selection will favour helping behaviours when benefits to kin, weighted by relatedness, outweigh personal costs.

Emlen’s Predictions on Family Dynamics
Stephen Emlen extended Hamilton’s ideas to explain the evolution of family living and cooperative breeding. He proposed that family stability depends on ecological and reproductive opportunities. Families should dissolve when better reproductive prospects arise elsewhere (as seen in the superb fairy wren). In resource-rich territories, families are more stable, potentially forming dynasties across generations (as with acorn woodpeckers). Helping behaviour and cooperative breeding tend to be strongest among close kin, as demonstrated in many bird and mammal species.

Eusociality in Insects
Eusociality, the highest level of social organization, is exemplified by bees, ants, and wasps. In these Hymenopterans, a haplodiploid genetic system means females share an unusually high relatedness (r = 0.75) with their sisters. This makes helping sisters reproduce more genetically advantageous than producing one’s own offspring. Colonies with monandrous queens (single mates) show higher relatedness and are more likely to evolve eusocial behaviour, while polyandrous queens (multiple mates) reduce relatedness and thus cooperation.

Conflict Within Families
Despite kinship promoting cooperation, it can also generate conflict. Parent-offspring conflict arises because parents must allocate limited resources among current and future offspring to maximise lifetime reproductive success. Offspring, in contrast, benefit from maximising their own share of parental investment. Sibling rivalry, a related phenomenon, occurs when siblings compete for scarce resources, as seen in egret chicks where asynchronous hatching produces dominance hierarchies and unequal survival outcomes.

Kin Recognition
For kin selection to operate effectively, animals must recognize their relatives. Mechanisms of kin recognition vary across species. Penguins, for instance, use unique vocal signatures to identify their chicks among thousands, whereas nest-building penguins rely more on spatial memory of nest locations. Matching models suggest that animals use internal “templates” to assess relatedness—these may be genetic, learned, or socially acquired—and can enable fine distinctions between degrees of kinship.

Overall, kinship theory unifies diverse animal behaviours—from altruistic calls and cooperative breeding to sibling competition and social insect colonies—under the principle that natural selection acts not just on individuals, but on genes shared among related individuals.

📋 BULLET-POINT SUMMARY

• Altruism puzzle: Why risk oneself (e.g., alarm calls)? → Genetic relatedness explains altruistic behaviour.

• Inclusive fitness: Sum of direct (own offspring) + indirect (kin’s offspring) fitness.

• Hamilton’s rule: Altruism evolves when rB > C.

• Belding’s ground squirrels:

  • Females call more often because they remain with kin.

  • Males disperse, reducing relatedness within groups.

• Kinship promotes cooperation and deters antisocial behaviour.

• Genetic relatedness (r):

  • Siblings = 0.5

  • Grandparent–grandchild = 0.25

  • Uncle/Aunt–Niece/Nephew = 0.25

  • Cousins = 0.125

• Emlen’s predictions:

  1. Families dissolve when better reproductive opportunities appear.

  2. High-resource territories → stable family “dynasties.”

  3. Cooperative breeding strongest among closest kin.

• Examples:

  • Superb fairy wrens: helpers disperse when breeding vacancies arise.

  • Acorn woodpeckers: remain in rich territories → dynasties.

• Eusocial insects:

  • Haplodiploid system (males haploid, females diploid).

  • Sisters share r = 0.75 → strong cooperation.

  • Monandrous queens → high relatedness; polyandry reduces eusociality.

• Parent-offspring conflict: Parents balance investment; offspring seek more.

• Sibling rivalry: Competition increases when resources are limited; older chicks often dominate.

• Kin recognition:

  • Penguins use vocal cues; nest-building species use spatial cues.

  • Matching models: internal “templates” (genetic or learned) to assess kinship.

🧠 40 MULTIPLE-CHOICE QUESTIONS (MCQs) WITH ANSWER KEY

1–10: Foundations of Kinship

1. Who introduced the concept of inclusive fitness?
   A) Darwin B) Hamilton C) Emlen D) Trivers
   ✅ Answer: B

2. Inclusive fitness includes:
   A) Only direct reproduction
   B) Both direct and indirect reproduction
   C) Only helping behaviour
   D) None of the above
   ✅ Answer: B

3. Hamilton’s rule can be expressed as:
   A) rC > B B) rB > C C) C > rB D) rB = C
   ✅ Answer: B

4. Genetic relatedness between siblings is:
   A) 0.25 B) 0.5 C) 0.75 D) 1.0
   ✅ Answer: B

5. In Belding’s ground squirrels, alarm calls are mostly made by:
   A) Males B) Females C) Juveniles D) All equally
   ✅ Answer: B

6. Female Belding’s squirrels call more because:
   A) They are braver
   B) They stay near kin
   C) They are more visible
   D) Males force them to
   ✅ Answer: B

7. The probability that two cousins share alleles identical by descent is:
   A) 0.5 B) 0.25 C) 0.125 D) 0.75
   ✅ Answer: C

8. Kinship affects animal behaviour by:
   A) Increasing selfishness
   B) Promoting cooperation and limiting conflict
   C) Eliminating competition
   D) Reducing reproduction
   ✅ Answer: B

9. Altruism is most favoured when relatedness (r) is:
   A) Low B) Moderate C) High D) Irrelevant
   ✅ Answer: C

10. Hamilton’s rule predicts helping behaviour if:
    A) Cost > benefit
    B) rB > C
    C) rB < C
    D) Benefit = cost
    ✅ Answer: B

11–20: Emlen’s Theory and Cooperative Breeding

11. Who expanded Hamilton’s theory to family living?
    A) Emlen B) Trivers C) Maynard Smith D) Wilson
    ✅ Answer: A

12. Emlen predicted families disintegrate when:
    A) Food is abundant
    B) New reproductive opportunities arise elsewhere
    C) Weather changes
    D) Predation increases
    ✅ Answer: B

13. In the superb fairy wren, helpers leave when:
    A) Breeding males die B) Food runs out C) Winter begins D) Females disperse
    ✅ Answer: A

14. Families on high-quality territories are:
    A) Less stable B) Unrelated C) More stable D) Short-lived
    ✅ Answer: C

15. Acorn woodpeckers form dynasties due to:
    A) Predator protection B) Resource-rich territories C) Climate D) Monogamy
    ✅ Answer: B

16. Cooperative breeding is most likely between:
    A) Unrelated individuals B) Closely related kin C) Rivals D) Random pairs
    ✅ Answer: B

17. Eusociality occurs mostly in:
    A) Mammals B) Reptiles C) Hymenoptera D) Fish
    ✅ Answer: C

18. Haplodiploid genetic systems are found in:
    A) Birds B) Insects like bees and ants C) Amphibians D) Mammals
    ✅ Answer: B

19. Relatedness between sisters in haplodiploid insects is:
    A) 0.25 B) 0.5 C) 0.75 D) 1.0
    ✅ Answer: C

20. Eusociality is more likely when queens are:
    A) Polyandrous B) Monandrous C) Monogamous with many males D) Asexual
    ✅ Answer: B

21–30: Conflict and Rivalry

21. Who proposed the parent-offspring conflict theory?
    A) Hamilton B) Trivers C) Darwin D) Emlen
    ✅ Answer: B

22. Parent-offspring conflict arises due to:
    A) Different optimal investment levels
    B) Equal food sharing
    C) Lack of resources
    D) Predator risk
    ✅ Answer: A

23. Kin selection predicts reduced aggression toward:
    A) Kin B) Non-kin C) Predators D) Mates
    ✅ Answer: A

24. Sibling rivalry intensifies when:
    A) Food is abundant B) Resources are limited C) Parents intervene D) Offspring mature
    ✅ Answer: B

25. Egret chicks often display:
    A) Equal sharing B) Asynchronous hatching dominance hierarchies
    C) Random feeding D) Cooperative feeding
    ✅ Answer: B

26. The most dominant egret chicks are usually:
    A) Last-hatched B) First-hatched C) Middle-hatched D) Oldest female
    ✅ Answer: B

27. Parent-offspring conflict affects:
    A) Predator defence B) Lifetime reproductive success
    C) Colouration D) Migration
    ✅ Answer: B

28. The genetic relatedness of an individual to itself is:
    A) 0.5 B) 0.75 C) 1 D) 0
    ✅ Answer: C

29. In sibling rivalry, individuals act as if:
    A) Kin should get equal shares
    B) Their own survival is more important
    C) Parents should decide
    D) None of the above
    ✅ Answer: B

30. Intense sib-sib competition in egrets leads to:
    A) Equal survival B) Age-related dominance C) No hierarchy D) Cooperation
    ✅ Answer: B

31–40: Kin Recognition

31. Kin recognition allows animals to:
    A) Identify predators B) Identify relatives C) Find food D) Choose territory
    ✅ Answer: B

32. Penguins recognize chicks using:
    A) Smell B) Visual markings C) Vocal signatures D) Nest smell
    ✅ Answer: C

33. Nest-building penguins rely on:
    A) Vocal cues B) Spatial memory C) Odour D) Colour cues
    ✅ Answer: B

34. Kin recognition is essential for:
    A) Kin selection B) Migration C) Foraging D) Camouflage
    ✅ Answer: A

35. The internal “template” in matching models may be formed:
    A) Genetically B) Through learning C) Socially D) All of the above
    ✅ Answer: D

36. Matching models suggest animals:
    A) Guess kinship randomly B) Match others against internal templates
    C) Avoid all kin D) Recognize only parents
    ✅ Answer: B

37. Kin recognition helps animals:
    A) Reduce inbreeding B) Increase cooperation C) Avoid aggression toward kin D) All of the above
    ✅ Answer: D

38. Penguins returning from the sea locate chicks primarily by:
    A) Smell B) Sound cues C) Visual landmarks D) None
    ✅ Answer: B

39. Kin recognition may be based on:
    A) Genetic cues B) Learned cues C) Both D) None
    ✅ Answer: C

40. Kinship theory integrates:
    A) Altruism, cooperation, and conflict
    B) Migration and feeding
    C) Mating systems only
    D) Physiology of hormones
    ✅ Answer: A