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Kin Selection & Inclusive Fitness

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Kin Selection & Inclusive Fitness

Social interactions between organisms present the opportunityfor conflict and cooperation

Social interaction

Performer benefits Performer suffers

Receiver benefits Cooperation Altruism

Receiver suffers Selfish Spiteful

•Cooperation, or mutualism, results in fitness gain for both participants•Selfish actions benefit the performer and hurt the receiver•Spiteful actions hurt both parties (hurt oneself to hurt another)•Altruism, the performer suffers in order to benefit the recipient

Altruism•

Behavior that benefits a receiver at a cost to the actor•

Honey bee sting, Alarm calls, Blood sharing by bats•

Cooperation: Displaying a behavior that benefits another individual. (If both benefit that's mutualism)

Altruism: Displaying a behavior that benefits another individual

at a cost to oneself.

‘Social behavior’ is NOT cooperative behavior : it is possible to have sociality with no cooperation and cooperation with no sociality.

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Evolution of Altruism

How can Altruism evolve?•

If the recipient of the altruistic act benefits, it is going to leave more offspring.

The actor however is not going to leave more offspring, or even fewer offspring –

fewer altruists in the next generation.•

If such behavior is heritable, and it goes on over many generations, it will ultimately die out.

Are there hidden benefits to helping somebody at a cost to yourself?–

Group selection –

rare, only if long-term assortment maintained–

Kin-selection –

yes, if helping relatives–

Sexual selection –

yes, if mating benefits–

Reciprocal altruism –

yes, if reciprocation likely and enforced–

Status –

yes, if indirect benefits

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Kin Selection•

Helping relatives increases your ‘inclusive fitness’:•

Inclusive fitness: your own offspring (‘fitness’) plus your genes reproduced in others.

This means that the more of your genes are in a relative, the more interest you have in helping them.

This is measured by “r”

(‘relatedness’), also called coefficient of relationship

“r”

is usually defined as the average proportion of alleles of an individual A that are identical by descent to those in individual B.

Or, the probability that A and B carry the same allele, derived from the same ancestor, at a particular locus.

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Kin SelectionHamilton’s rule:•

An individual can be altruistic ifc <

b * r•

The cost should be smaller than the benefit multiplied by relatedness.

E.g. an individual may not reproduce in a given year (c=1) to help its sibling (r=0.5) if this helps the sibling raise at least two additional offspring (b=2).

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Question:

Would you lay down your life for your brother?

“No, but I would for two brothers or eight cousins”

J.B.S. Haldane

Relatedness

If you have two children, on average one copy of each of your genes survives.

If you have four nieces, on average one copy of each of your genes survives.

This means, if you sacrifice yourself for four nieces, ‘your genes’

have lost nothing.

Relatedness = 0.5

Relatedness = 0.25

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Conditions for altruism towards genetic relatives (kin) set by Hamilton’s rule:

b/c

> 1/r

b = benefits to recipientc = cost to donorr = coefficient of relatedness

Relationship r

mother-offspring 1/2

sister-brother

1/2

uncle-nephew

1/4

cousin-cousin

1/8If r = 1/2, then benefit b must ≥

2c.

Inclusive fitness

W.D. Hamilton (1964)•

An individual increases its fitness either through own personal reproduction OR reproduction of genetic relatives

Inclusive fitness

is fitness due to both forms of reproduction

10_IB lecWEB_Papaj-1.ppt

Kin Selection•

When it is demonstrated that individuals preferentially help kin

rather than non-kin, this is taken as evidence for kin-selection.

Examples for kin-selection:–

social insects–

prairie dog alarm calls to offspring & other relatives–

generally parental careKin-recognition•

Do individuals have to be able to recognize relatives for kin selection to work?

NO –

kin selection can operate, and cause the evolution of altruism, as long as altruists are more likely to help kin than non-kin -

for whatever reason.

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Females fightingMales playing

Cooperation between male chimpanzees is greater than cooperation between females.

In chimps, females disperse from natal troop, whereas males often stay.

Hence, males in a troop are more geneticallyHence, males in a troop are more genetically--related to each other.related to each other.

10_IB lecWEB_Papaj-1.ppt

•Highly social mammal; breeds in colonies•Females tend to breed near their birthplace•Neighbors are often closely related •Squirrels “trill”

when predatory mammals are present and “whistle”

when hawks are seen•Individuals that whistle have lower mortality than those that do not (selfish)•Individuals that trill have higher mortality than those that do not (altruistic)

Alarm calling: Belding’s Ground Squirrel

Age (months)

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oved

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(m)

Coo

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lecture 08 -

kin selection + eusociality.pptlecture 19-21 Kin Selection and social behavior.ppt

From Sherman et al. 1977

Females were much more likely to call than males

Females were much more likely to call when they had a close relative nearby --thus, altruistic actions are not randomly distributed

lecture 08 -

kin selection + eusociality.ppt

Alarm calling: Belding’s Ground Squirrel

Kin Selection in White-Fronted Bee-EatersIn many birds, young will help their parents rear new offspring,

rather than go off and reproduce themselves

•New offspring may be full or half-

siblings of the young helpers

•Common in species where opportunities for breeding or new nest construction are limited

•In these cases, the young helping their parents may be making the best of a bad situation

lecture 08 -

kin selection + eusociality.ppt

•Bee-Eaters live in big colonies, where relatives and non-relatives nest in close proximity, as part of the same clan (= nesting group)

•1-yr olds often help at an existing nest instead of starting their

own

•Prediction: coeff. of relatedness should dictate whether birds help clan-mates

(1)

Unrelated birds that have “married”into a clan are much less likely to help than a blood relative born intothe clan (= natal)

(2) Young selectively help more closely related adults (coefficient of relatedness predicts how help will be distributed)

Kin Selection in White-Fronted Bee-Eaters

(birds that haven’t yet reproduced)

This makes a huge difference to parents

Half of bee-eater babies starve to death before leaving the nest

Each 1-yr old helper results in 0.47 moreoffspring being successfully raised

--major boost to inclusive fitness

Kin Selection•

Inclusive fitness theory vs. kin selection•

In fact, that’s why some argue that it should be called ‘inclusive fitness theory’

rather than ‘kin selection’

Altruism can evolve as long as altruists are more likely than chance to dispense help to other altruists.

Kin-recognition•

By smell (rodents, humans, insects)•

By song (some birds)•

By learning/familiarity (mice, humans)•

By visual similarity (chimpanzees, humans)

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Kin Selection & Eusociality•

Eusociality: some individuals sterile (caste)•

Evolved > 10 times in Hymenoptera (haplodiploid)•

All members of a colony are usually highly related•

Haplodiploidy: sex determining mechanism in which males are haploid (1N) and females diploid (2N).

Haplodiploidy

cause relatedness asymmetry•

Does haplodiploidy

cause eusociality?•

In complete monogamy, workers are more related to the queen’s daughters (sisters) (r=0.75) than to their own (r=0.5)

Worker bees can benefit by foregoing reproduction and helping queen rear more sisters

This would explain why so many Hymenoptera are eusocial

and why workers are always females

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Kin Selection & Eusociality•

However, workers are only related to males by r=0.25 (less than to daughters) –

thus average relatedness to reproductive offspring is still 0.5 (depending on sex ratio)

Actual relatedness values measured in insect colonies are almost never 0.75 (multiple queens, polygamy)

Some eusocial

species lack haplodiploidy

Sterile Castes in Naked Mole Rats–

Occur in colonies of up to 300 members. –

Breeding restricted to a single queen.–

Inbreeding results in high relatedness•

Many haplodiploid

species are not social

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Facultative Eusociality

Totipotency

of only the more reproductive caste

Multi-foundress

nests grew fastest when there was a big difference in body size between the dominant queen and her subordinates

-less time lost to challenges to the dominant queen by her underlings (fighting for the right to lay more eggs)

Subordinates may help instead of starting your own nest becausesubordinates are close relatives of the dominant foundress

Possible strategies:-strike out on your own, risk it

-help a close relative, thereby increasing your inclusive fitness

-sit and wait: don’t help anyone, but wait for chance to steal a nest should a foundress

die or you can beat her up later

-leave nest in early spring, hibernate, try again next season

-reproductive altruism is facultative, meaning it can be adopteddepending on the conditions faced by a particular female

-relatedness-body size-nest availability-time of year (season)

Facultative Eusociality

Eusociality•

Alternative hypotheses for the origin of eusociality:–

Parental manipulation–

Predisposition to sociality because of high b/c

ratio (underground nests, extended brood care)

Group selection•

Wilson & Hölldobler

2005–

Superiority of colony life over solitary life (b may be much greater than c)–

Eusociality

arose among unrelated individuals first; then relatedness increased–

In many species nests are founded by unrelated individuals–

Real-existing relatedness low and counterproductive (?)–

Eusociality

rare even in highly related groups•

Conclusions from the controversy–

Haplodiploidy

is not crucial to evolution of eusociality–

Ecological factors (high b/c) explain most of the variation between species in sociality–

Controversy arises over the definition of ‘r’

relatedness by pedigree or measure of genetic similarity?

Complete worker sterility can only arise with positive r, whether by kinship or other segregation mechanisms

However, many social insects do not actually have complete worker sterility

http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf

Kin Selection and Parental Care•

Predictions of kin selection about parental care•

Individuals should invest in (care for) their own offspring versus unrelated young

http://instruct.uwo.ca/zoology/336a/lecture4handout.pdf

Kin selection in Bluegill

Hain and Neff 2006

Kin Selection and Mating System•

Within nests, the average relatedness of parentals’

offspring is >3x that of cuckolders’

offspring•

Thus, a parental’s

offspring could gain more kin-selective benefits than a cuckolder’s

offspring simply by associating with and helping a random nestmate

Kin discrimination may be important when there is an optimal group size that limits membership or when food resources are limited and shared among group members.

Hain and Neff 2006

But, to gain a similar kin-selective benefit, a cuckolder’s

offspring would have to actively discriminate among nestmates, which they do via a self-

referent odor mechanism•

Experimental evidence from behavioral trial that separate kin recognition from familiarity

Reciprocal altruism•

Altruistic behavior among unrelated individuals•

Trivers

(1971) hypothesized that individuals may be selected to dispense altruistic acts if equally-valuable favors are returned in the future (Reciprocal altruism)

May evolve if:–

The cost to the actor is less than or equal to the benefit to the recipient–

Individuals that do not reciprocate are punished•

May evolve when:–

Interactions generally take place among the same sets of individuals–

Many opportunities for altruistic behavior exist–

Individuals have good memories–

Costs vs. benefits are roughly equal

Blood sharing in Vampire Bats•

Roost in hollow trees•

High levels of “association”

in roosting behavior•

Regurgitate blood meals to one another: 33% of young bats and 7% of adults fail to feed on any given night

Kin selection or reciprocal altruism?

Blood sharing in Vampire BatsFive criteria to distinguish reciprocity vs

kin selection (Wilkinson 1990):1: Females associate for long periods, so there are numerous chances to be

either the donor or recipient bat.2: The likelihood of regurgitation to roostmates

can be predicted on the basis of past associations.

3: The roles of donor and recipient reverse often.4: The short-term benefits to the recipient outweigh the costs to the donor.5: Donors can recognize and expel cheaters to this system.

☺☺

☺☺

?

Kin selection or reciprocal altruism? Probably a little of both(most sharing between mother-pups, but also between unrelated buddies)