Kin Selection &
Inclusive Fitness
Social interaction
Social interactions between organisms present the opportunity
for conflict and cooperation
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
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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
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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?
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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
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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 Selection
Hamilton’s rule:
• An individual can be altruistic if
c<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).
Question: Would you lay down your life for
your brother?
“No, but I would for
two brothers
or eight cousins”
J.B.S. Haldane
http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf
Relatedness
Relatedness = 0.25
Relatedness = 0.5
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If you have two
children, on average
one copy of each of
your genes survives.
http://eebweb.arizona.edu/Courses/Ecol600A/kin%20selection.pdf
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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.
Conditions for altruism towards genetic relatives (kin) set by Hamilton’s rule:
b/c > 1/r
b = benefits to recipient
c = cost to donor
r = coefficient of relatedness
If r = 1/2, then benefit b must ≥ 2c.
Relationship
r
mother-offspring
1/2
sister-brother
1/2
uncle-nephew
1/4
cousin-cousin
1/8
Inclusive fitness
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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
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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 care
Kin-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
Males playing
Females fighting
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 genetically-related to each other.
10_IB lecWEB_Papaj-1.ppt
Alarm calling: Belding’s Ground Squirrel
Distance moved from
natal burrow (m)
Cooperation in chasing
“trespassing” squirrels
•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)
Age (months)
lecture 19-21 Kin Selection and social behavior.ppt
lecture 08 - kin selection + eusociality.ppt
Alarm calling: Belding’s Ground Squirrel
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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
From Sherman et al. 1977
lecture 08 - kin selection + eusociality.ppt
Kin Selection in White-Fronted Bee-Eaters
In many birds, young will help their parents rear new offspring, rather than go
off and reproduce themselves
•New offspring may be full or halfsiblings 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
•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
lecture 08 - kin selection + eusociality.ppt
Kin Selection in White-Fronted Bee-Eaters
(birds that haven’t yet reproduced)
(2) Young selectively help more closely related
adults (coefficient of relatedness predicts
how help will be distributed)
(1) Unrelated birds that have “married”
into a clan are much less likely to
help than a blood relative born into
the clan (= natal)
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 more
offspring being successfully raised
--major boost to inclusive fitness
Kin Selection
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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
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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
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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
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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 because
subordinates are close relatives of the dominant foundress
Facultative Eusociality
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 adopted
depending on the conditions faced by a particular female
-relatedness
-body size
-nest availability
-time of year (season)
Eusociality
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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
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Wilson & Hölldobler 2005
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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
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Predictions of kin selection about parental care
Individuals should invest in (care for) their own offspring versus
unrelated young
Kin selection in Bluegill
http://instruct.uwo.ca/zoology/336a/lecture4handout.pdf
Hain and Neff 2006
Kin Selection and Mating System
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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.
But, to gain a similar kin-selective
benefit, a cuckolder’s offspring would
have to actively discriminate among
nestmates, which they do via a selfreferent odor mechanism
Experimental evidence from
behavioral trial that separate kin
recognition from familiarity
Hain and Neff 2006
Reciprocal altruism
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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
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May evolve when:
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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
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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 Bats
Five 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.
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Kin selection or reciprocal altruism? Probably a little of both
(most sharing between mother-pups, but also between unrelated buddies)