new t h u rsd a y, s e p te m b e r 2 6 , 1...
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Helpful behaviorsAlarm calls (e.g., Belding ground squirrel)
Sentinel behavior (e.g., meerkats)
Nest helping
Eusocial behavior
Actor performs some action that benefitsanother (the recipient).
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How do you explain the evolution ofhelpful behavior?
Mutualism (actor benefits)
Reciprocal altruism (actor eventually benefits)
Kin selection (indirect selection)
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Interaction Social Donor Social Recipient
Mutualism + +
Reciprocity + (delayed) +
Altruism - +
Selfishness + -
Spitefulness - -
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Mutualism
Groups of lions can bring down largerprey and better defend the preyfrom other lions and hyenas.
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Bluegill Male: Males form nest sites of 50to 100 males. Mutualistic because predationis lower if your nest is surrounded by others.
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Male lions will often cooperate in oustingresident males from a pride, or in defendinga pride from other (outside) groups of males.Often, the males in a pride are closely related.
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Reciprocal Altruism
Repeated interactions between individuals
Many opportunities for altruism
Good memories
Potential altruists interact in symmetrical situations
Dispense an altruistic (beneficial) act, whichis later returned as an equally beneficial act.
Most likely when:
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Groomer helps groomee by removing parasites & debris
Favor is returned in baboon femalesThursday, September 26, 13
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Females hang out together in groups of about 10
Often fail to feed (on blood!) in a given night
Will share blood by regurgitating blood meals to others
Share more frequently with relatives, nestmates, and those that shared with them earlier.
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“Would I lay down my life to save my brother?No, but I would to save two brothers or eightcousins.”
— JBS Haldane
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“The Creator, if He exists, has a special preference for beetles.”
“ Four stages of acceptance: i) this is worthless nonsense; ii) this is an interesting, but perverse, point of view; iii) this is true, but quite unimportant; iv) I always said so.”
“Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we CAN suppose.”
— JBS Haldane
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William Hamilton (1936–2000)
Hamilton, W. D. 1964. The genetical evolution of social behavior, I and II. J. Theor. Biol. 7:1-52.
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Kin SelectionHamilton’s rule: A gene for altruistic selfsacrifice will spread through a population if the cost to the altruist is outweighedby the benefit to the recipient devaluedby a fraction representing the geneticrelatedness between the two.
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Br − C > 0
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Actor Recipient
SharedParent
Actor Recipient
FatherMother
Half-siblings Full-siblings
r = 1/4 r = 1/2
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Eusociality
Overlap in generations between parents and offspring
Cooperative brood care
Specialized castes of nonreproductive individuals
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Sister Brother
Father(haploid)
Mother(diploid)
Haplodiploidy
r(sister-sister) = 3/4r(sister-brother) = 1/4r(mother-daughter) = 1/2r(mother-son) = 1/2
1/21/2
Sister Sister
Father(haploid)
Mother(diploid)
Haplodiploidy
1/21/2 11/2
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Because sisters are highly related, a female worker should bias her help towards repro-ductively competent sisters, rather thantoward her brothers.
The queen is equally related to sons and daughters, and favors equal investment ineach.
Conflict between queen and daughters(parent-offspring conflict).
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Sisters share three times more genes witheach other than with brothers. This favorsa stable investment ratio of 3:1 in favorof sisters.
Queen wants a 1:1 investment.
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Are hymenopteran colonies biased in theirallocation of resources to males/females?
Yes: ! (1) Trivers and Hare (1976) found the expected 3:1 investment ratio (weight of all female reproductives vs. male reproductives).! (2) Mueller (1991) showed that worker hymenopterans can alter their invest- ment in colony mates depending on their relatedness.
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Mueller (1991)
When a colony is founded by a single female, the asymmetry in relatedness (r=3/4) persists, and workers invested more energy in females.
If queen is removed, a worker takes over her role. Now workers are helping raise their nieces (r=0.375) and nephews (r=0.375). The investment in males increases.
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Naked mole rat
Live underground in groups of up to 200 individualsBreeding restricted to a single “queen” and to several “kings”Others are non-reproductive and act as workersDiploid, but colonies composed of closely related individuals (inbred, r is about 0.81)Up to 85% of all matings are between parents and their offspring, or between full sibs.
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