1. Kin Selection and Social Behavior  Interactions between individuals can have 4 possible outcomes in terms of fitness gains for the participants.

2. Kin Selection and Social Behavior  Cooperation (mutualism): fitness gains for both participants.  Altruism: instigator pays fitness cost, recipient benefits.  Selfishness: instigator gains benefit, other individual pays cost.  Spite: both individuals suffer a fitness cost.

3. Kin Selection and Social Behavior  No clear cut cases of spite documented. The behavior clearly harms the instigator for no benefit so difficult to see how it could be favored by selection.  Selfish and cooperative behaviors easily explained by selection theory because they benefit the instigator.

4. The puzzle of altruism  Altruism is hard to explain because the instigator pays a cost and another individual benefits.  How can selection favor the spread of an altruistic allele that produces a behavior that benefits other individuals at the expense of individuals bearing the altruistic allele?

5.  BTW when I say “an allele that ‘produces a behavior’ I don’t mean that the allele literally directly codes for the behavior.  An allele directly code for the structure of proteins.  However, proteins interact with other proteins and the result of all these biochemical interactions in building a brain can result in an organism with one version of an allele behaving somewhat differently from an individual with a different version.

6. The puzzle of altruism  For Darwin altruism presented a “special difficulty, which at first appears to me insuperable, and actually fatal to my whole theory.”  Darwin suggested however that if a behavior benefited relatives, it might be favored by selection.

7. The puzzle of altruism  W.D. Hamilton (1964) developed a model that showed how an allele that favored altruistic behavior could spread under certain conditions.

8. Coefficient of relatedness  Key parameter is the coefficient of relatedness: r.  r is the probability that the homologous alleles in two individuals are identical by descent (see earlier notes on inbreeding for the concept of identical by descent— basically copies of an allele being inherited from a particular individual).

9. Calculating r  Use a pedigree to calculate r.  Pedigree shows all possible direct routes of hereditary connection between the two individuals.  Because parents contribute half their genes to each offspring, the probability that alleles are identical by descent for each step is 50% or 0.5.

10. Calculating r  To calculate r:  (i) Trace each unique path between the two individuals via common ancestors and count the number of steps needed.  (ii) For this path r = 0.5 (number of steps). Thus, if two steps r for this path = 0.5 (2) = 0.25.  (iii) To calculate final value of r you add together the r values calculated from each path.

14. Hamilton’s rule  Given r the coefficient of relatedness between the actor and the recipient, Hamilton’s rule states that an allele for altruistic behavior will spread if  Br - C >0  Where B is benefit to recipient and C is the cost to the actor. Unit of measurement for B and C is surviving offspring.

15. Hamilton’s rule  Altruistic behaviors are most likely to spread when costs (C) are low, benefits (B) to recipient are high, and the participants are closely related (r is large).

16. Applying Hamilton’s rule  You have a food item that is worth 2 units of benefit to you.  You have a tiny nephew for whom the food would be worth 10 units of benefit.  Should you eat the food or give it to your nephew?

17. Applying Hamilton’s rule  The value of r for a nephew is ¼.  Cost to you would be 2 (as you’re giving up 2 units of benefit).  Benefit to nephew is 10.  Is Br - C >0?  10(¼) – 2 = ?  2.5 - 2 = 0.5. This is > 0 so you should give the food to your nephew.  Should you share with a cousin? r = 1/8 for a cousin.

18.  Share with a cousin?  No because Br - C is not > 0.  10 *1/8 – 2 = 1.25 – 2 = -0.75

19. Inclusive fitness  Hamilton invented the idea of inclusive fitness which divides an individual’s fitness into two components:  Direct fitness results from an individual’s personal reproduction (the babies it produces)  Indirect fitness results from additional reproduction by relatives, that is made possible by an individual’s actions. For example an individual might help feed its sisters offspring or guard them from predators.

20. Kin selection  Natural selection favoring the spread of alleles that increase the indirect component of fitness is called kin selection.

21. Alarm calling in Belding’s Ground Squirrels  Giving alarm calls alerts other individuals but may attract a predator’s attention.  Belding’s Ground Squirrels give two different calls depending on whether predator is a predatory mammal (trill) or a hawk (whistle; Sherman 1985).

22. http://michaelfrye.com/yosemite- journal/?p=375

23. Is alarm calling altruistic?  Sherman and colleagues observed 256 natural predator attacks. https://www.flickr.com/photos/charlespan/6527465145/

24. Belding’s Ground Squirrels  In hawk attacks whistling squirrel is killed 2% of the time whereas non-whistling squirrels are killed 28% of the time.  Calling squirrel appears to reduce its chance of being killed.

25. Belding’s Ground Squirrels  In predatory mammal attacks trilling squirrel is killed 8% of the time and a non- trilling squirrel is killed 4% of the time. http://captainkimo.com/coyote-on-the-hunt-pouncing-for-prey-at-yellowstone-national- park/

26. Belding’s Ground Squirrels  Calling squirrel thus appears to increase its risk of predation.  Whistling appears to be selfish, but trilling altruistic.

27. Belding’s Ground Squirrels  Belding’s Ground Squirrels breed in colonies in Alpine meadows.  Males disperse, but female offspring tend to remain and breed close by. Thus, females in colony tend to be related.

28. Belding’s Ground Squirrels  Sherman had pedigrees that showed relatedness among his study animals.  Analysis of who called showed that females were much more likely to call than males.

30. Belding’s Ground Squirrels  Females were also more likely than males to call when they had relatives within earshot.

32. Belding’s Ground Squirrels  Relatives also cooperated in behaviors besides alarm calling.  Females were much more likely to join close relatives in chasing away trespassing ground squirrels than less closely related kin and non-kin.

34. Belding’s Ground Squirrels  Overall, data show that altruistic behavior is not randomly directed.  It is focused on close relatives and should result in indirect fitness gains by increasing the survival prospects of these relatives and hence their future reproduction.

35. Kin selection and cannibalism in tadpoles  Spadefoot toad tadpoles come in two morphs.  Typical morph is omnivorous mainly eats decaying plant material.  Cannibalistic morph has bigger jaws and catches prey including other spadefoot tadpoles.

36. Kin selection and cannibalism in tadpoles  Pfennig (1999) tested whether cannibals discriminate between kin and non-kin.  Placed 28 cannibalistic tadpoles in individual containers. Added two omnivorous tadpoles (tadpoles had never seen before) to each container. One was a sibling, the other non-kin.

37. Kin selection and cannibalism in tadpoles  Pfenning waited until cannibal ate one tadpole, then determined which had been eaten.  Found that kin were significantly less likely to be eaten. Only 6 of 28 kin were eaten, but 22 of 28 non-kin.

39. Kin selection and cannibalism in tadpoles  Pfennig also studied tiger salamanders whose tadpoles also develop into cannibalistic morphs.  Kept 18 cannibals in separate enclosures in natural pond. To each enclosure added 6 siblings and 18 non-kin typical morph tadpoles.

40. Kin selection and cannibalism in tadpoles  Some cannibals discriminated between kin and non-kin. Others did not.  Degree of relatedness to siblings = 1/2

41. Kin selection and cannibalism in tadpoles  Thus, by Hamilton’s rule discrimination in favor of kin favored if B(r) - C > 0  Benefit estimated by counting number of siblings that survived. Siblings of discriminating cannibals twice as likely to survive as siblings of non-discriminating cannibals.

42. Kin selection and cannibalism in tadpoles  Benefit thus approximately 2.  Cost assessed by evaluating effect of not eating siblings by comparing growth of discriminating and non-discriminating cannibals. No difference in growth rates. Cost then estimated as close to 0.

44. Kin selection and cannibalism in tadpoles  By Hamilton’s rule discrimination should be favored because 2(1/2) - 0 = 1 which is >0.

45. Altruistic sperm in wood mice  Moore et al. have demonstrated altruistic behavior by sperm of European wood mice.  Females highly promiscuous. Males have large testes and engage in intense sperm competition with other males.

46. Altruistic sperm in wood mice  Wood mice sperm have hooks on their heads. And connect together to form long trains of sperm that can include thousands of sperm.  Swimming together sperm travel twice as fast as if they swam separately.

47. http://phenomena.nationalgeographic.com/ 2014/07/23/these-mice-excel-at- assembling-the-ideal-sperm-swim-teams/

49. Altruistic sperm in wood mice  To fertilize egg, train must break up.  To break up train many sperm have to undergo acrosome reaction releasing enzymes that usually help fertilize an egg.

50. Altruistic sperm in wood mice  Releasing these enzymes before reaching an egg means these sperm cannot fertilize the egg. These sperm sacrifice themselves.  Because other sperm carry half of the same alleles, sacrifice makes sense in terms of kin selection.

51. Discrimination against non-kin eggs by coots  Important to avoid paying costs on behalf of non-kin.  Lyon (2003) studied defense against nest parasitism in American coots.  Coots often lay eggs in other coot’s nests in hopes of having them reared.

52. Discrimination against non-kin eggs by coots  Accepting parasitic eggs is costly because half of all chicks starve and same number reared in parasitized and non-parasitized nests.  Thus, host parent loses one offspring for every successful parasite.

53. Discrimination against non-kin eggs by coots  Because of high cost of being parasitized and lack of benefit (assuming parasites are non-kin) Hamilton’s rule predicts coots should discriminate against parasitic eggs.  Coot eggs very variable in appearance. If 2 eggs laid within 24 hours Lyon knew one was a parasite.

54. Discrimination against non-kin eggs by coots  Among 133 hosts 43% rejected one or more parasitic eggs. Rejected eggs differed from hosts eggs significantly more than did accepted eggs.

56. Discrimination against non-kin eggs by coots  Females who accepted eggs laid one fewer egg of their own for each parasitic egg they accepted. Average total clutch (including parasites) 8 eggs,

58. Discrimination against non-kin eggs by coots  Females who rejected eggs laid an average of 8 of their own eggs even though they waited to finish laying before disposing of eggs they were rejecting. Coots can count!  By counting eggs and rejecting extras that do not look right coots prevent themselves from being parasitized.

60. Parent-offspring conflict.  Parental care is an obvious form of altruism. In many species parents invest huge quantities of resources in their offspring.  Initially, parent and offspring agree that investment in the offspring is worthwhile because it enhances the offspring’s prospects of survival and reproduction.

61. Parent-offspring conflict.  However, a parent shares only 50% of its genes with the offspring and is equally related to all of its offspring, whereas offspring is 100% related to itself, but only shares 50% of genes with its siblings.  As a result, at some point a parent will prefer to reserve investment for future offspring rather than investing in the current one, while the current offspring will disagree. This leads to a period of conflict called weaning.

62. Parent-offspring conflict.  The period of weaning conflict ends when both offspring and parent agree that future investment by the parent would be better directed at future offspring. This is when the benefit to cost ratio drops below ½.

63. Fig 11.18 Figure shows B/C benefit to cost ratio of investing in the current offspring. Benefit is measured in benefit to current offspring and cost is measured in reduction in future offspring.

64. Parent-offspring conflict  In instances where parents produce only half siblings we should expect weaning conflict to last longer because the current offspring is les closely related to future offspring.  This has been confirmed in various field studies.

66. Siblicide  In many species there is intense conflict between siblings for food that may result in younger weaker chicks starving to death.  In other species regardless of food supplies first hatched offspring routinely kill their siblings.

67. Siblicide  For example, in Black Eagles the first hatched chick hatches several days before its sibling. When the younger chick hatches its older sibling attacks and kills it.

68. Siblicide  In species such as Black Eagles siblicide is obligate in that the younger offspring is always killed. Black Eagles are only capable of rearing one young.  The most likely explanation for the later hatched young is that for the parents it serves as an “insurance offspring” in case the first offspring fails to hatch or develop.

69. Siblicide  In other species such as Cattle Egrets there is intense conflict that establishes a clear age-based hierarchy in the brood that determines how food is divided among the brood members.  In cattle egrets, younger chicks usually starve, but if it is a good food year they often fledge.

70. Siblicide  Siblicide is thus facultative in cattle egrets because restraint by the older chicks in not killing the younger siblings can be rewarded in good years.  In Black Eagles there is no prospect of two young being reared, so the older chick ensures its own survival by eliminating its sibling.

71. Siblicide  Siblicide shows that relatedness does not necessarily lead to altruistic behavior. For Cattle Egrets and Black Eagles selfishness is better because the costs of altruism are too high.

72. Reciprocal Altruism  Some animals occasionally behave altruistically towards non-relatives.  Such behavior is adaptive if the recipient is likely to return the favor in the future.

73. Reciprocal altruism  Reciprocal altruism most likely in social animals where individuals interact repeatedly because they are long-lived and form groups, and also when individuals have good memories.

74. Reciprocal altruism in Vampire bats  E.g. Vampire Bats. Feed on blood and share communal roosts.  Bats may starve if they fail to feed several nights in a row.  However, bats who have fed successfully often regurgitate blood meals for unsuccessful bats.

75. Reciprocal altruism in Vampire bats  Cost of sharing some blood is relatively low for donor bat but very valuable for recipient.  Research shows that Vampire bats share with relatives, but also share with individuals who have shared with them previously and with whom they usually share a roost.

76. Association is measure of how frequently two individuals associate socially. Regurgitators regurgitate to individuals they associate with regularly.