Transcript Document

Conflict and Cooperation
Lecture 7
Lecture Outline
1.
Evolutionary game theory
2.
Sexual selection
3.
Kin selection and the evolution of cooperation
4.
Selfish genes
John Maynard Smith
John Nash
William Hamilton
Evolutionary Game Theory
Evolutionarily Stable Strategy (ESS) is a strategy which, if adopted by a
population of players, cannot be invaded by any alternative strategy that is
initially rare
Payoff Matrix
H
D
H w(H,H) w(H,D)
D w(D,H) w(D,D)
• Interactions between 2 individuals, each of
which has 1 of 2 or more phenotypes (strategies)
{H,D}
• For each possible pairwise combination of
strategies, an individual has a different payoff
w(H,D)
• The payoff depends not only on the individual’s
own phenotype, but also on that of the
individual it interacts with
w(H,H)≠w(H,D)
Evolutionary Game Theory
The fitness of phenotypes H and D are:
w(H) = p w(H,H) + (1-p) w(H,D)
w(D) = p w(D,H) + (1-p) w(D,D)
where p is the frequency of H in the population
H is an ESS if:
w(H)>w(D)
If D is a rare mutant (p≈1) this condition implies that:
either
(a) w(H,H)>w(D,H)
or
(b) w(H,H)=w(D,H) and w(H,D)>w(D,D)
Evolutionary Game Theory
Hawk-Dove Game
One of the earliest problems to which evolutionary game theory was applied
was conflict between males competing for resources
Hawk:
H
Dove: D
H
D
½ (VC)
V
0
½V
Hawk
Escalate a conflict until it is injured
(with cost C) or until it gains the
contested resource (with gain V)
Dove
Retreats when threatened neither
gaining nor loosing fitness
When 2 phenotypes of the same kind
coincide they have equal chances of wining
or losing
Evolutionary Game Theory
Hawk-Dove Game
Hawk:
H
Dove: D
H
D
½ (VC)
V
0
½V
Pure Strategies
Play always the same strategy
Is Dove an ESS?
Is Hawk an ESS?
• If V>C it pays to be a Hawk
• If V<C no pure strategy is an ESS
Evolutionary Game Theory
Hawk-Dove Game
Hawk:
H
Dove: D
H
D
½ (VC)
V
0
½V
Mixed Strategies
Play sometimes one strategy and sometimes the other
Is there a mixed ESS?
A mixed strategy p* requires that
w(H)=w(D)
p* ½(V-C)+(1–p*) V= p* 0+(1–p*) ½V
and p*=V/C (playing Hawk with probability V/C) is a mixed ESS
The optimal behavior is variable and contingent on the values V and C
Evolutionary Game Theory
Hawk-Dove-Assessor Game
Payoff Matrix
Assessor Strategy
H
D
A
Hawk: H
½(V-C)
V
½(V-C)
Dove: D
0
½V
¼V
½V
¾V
½V
Assessor: A
Display first and escalate the conflict
only if it judges the opponent to be
smaller or weaker.
If larger plays Hawk and wins if
smaller play Dove avoiding the cost
Assumptions:
• The probability of being larger is
50%
• Assessment is costless and
accurate
Evolutionary Game Theory
Hawk-Dove-Assessor Game
H
D
A
Hawk: H
½(V-C)
V
½(V-C)
Dove: D
0
½V
¼V
½V
¾V
½V
Assessor: A
Pure Strategies
Is Hawk an ESS?
Is Assessor an ESS?
Many animals react aggressively or not depending on their opponents size or
correlated features
Evolutionary Game Theory
Hawk-Dove-Assessor Game
Many animals react aggressively or not depending on their opponents size or
correlated features
Male toads that clasps females before the eggs are laid and fertilized are often
aggressively displaced by larger males but not by smaller ones. A male is unlikely
to try to displace a mounted male that is larger than himself
Evolutionary Game Theory
Hawk-Dove-Assessor Game
Evolutionary Game Theory
Hawk-Dove-Assessor Game
14/50 approaches result into
fight
Evolutionary Game Theory
Hawk-Dove-Assessor Game
Honest signals of the of the individual’s fighting ability or resource-holding
potential
Deceptive signals indicating greater fighting ability than the individual actually
has
Deceptive signals should be unstable in evolutionary time because selection
would favor genotypes that ignored the signals, which having lost their utility
would be lost in subsequent evolution
Dishonest signals
however are not
uncommon
Male fiddle crab
Uca annulipes
Sexual Selection
Concept
Describes differences among individuals of a sex in the number of reproductive
capacity of mates they obtain
Sexual Selection
Concept
Sexual selection exists because females produce relatively few large gametes
(eggs) and males produce many small gametes (sperm)
This difference creates an automatic conflict between the reproductive
strategies of the sexes:
• A male can mate with many females and he often suffers little reduction in
fitness if he should mate with an inappropriate female
• A female can be fertilized by a single male and her fitness can be
significantly lowered by inappropriate mating
Sexual Selection
Concept
The operational sex-ratio (relative number of males and females in the mating
pool) is often male-biased because males mate more frequently
Females are a limiting resource for males but males are not
Variation in mating success is generally greater among males than females and is
a measurement of the intensity of sexual selection
Phalaropes: Sex-Role Reversal
Phalaropus fulicarius
Sexual Selection
Sexual Selection
Contests Between Males and Between Sperm
Contest among males for mating opportunities
Antlers of red deer
Cervus elaphus
Canine teeth of the babirusa
Babyrousa babyrussa
Directional selection for greater size, weaponry or display features can cause an
arms race
Such escalation becomes limited by opposing ecological selection if the cost of
larger size or weaponry becomes sufficiently great
Sexual Selection
Contests Between Males and Between Sperm
Males reduce the likelihood that other males’ sperm will fertilize a female’s eggs
Lateral Horn
In many damselflies, the male’s
genitalia are adapted to remove
the sperm of previous mates from
the female’s reproductive tract
Sperm competition
Spinelike hairs
and clump of
rival’s sperm
Penis of the black-winged damselfly
Calopteryx
Occurs when the sperm of two or
more males have the opportunity
to fertilize a female’s eggs
Sexual Selection
Sexual Selection by mate choice
Sexual Selection
Sexual Selection by mate choice
Individuals of one sex (usually male) compete to be chosen by the other
Females mate preferentially with
males that have larger, more
intense, or more exaggerated
characters
The preferred male characters are
often ecologically disadvantageous
Tungara Frogs
Physalaemus
pustulosus
Frog-eating Bats
Trachops cirrhosus
Female choosiness may likewise have costs: the time spent searching for
acceptable males has been shown to reduce reproductive output in several
species
Sexual Selection
Sexual Selection by Mate Choice
Why should females have a preference for these traits, especially for features
that seem arbitrary and dangerous the males bearing them?
1.
Sensory bias
2.
Direct benefit to choosy females
3.
Indirect benefit to choosy females
a. Runaway sexual selection
b. Indicators of gene quality
4.
Antagonistic coevolution
Sexual Selection
Sexual Selection by mate choice
Sensory Bias
Certain traits may be intrinsically stimulating and evoke a greater response
simply because of the organization of the receptor’s sensory system
In some species of the fish
genus Xiphophorus part of the
male tail is elongated into a
“sword”
Females preferred males with
swords not only in
Xiphophorus but also in the
swordless genus Priapella
Sexual Selection
Sexual Selection by mate choice
Direct Benefit to Choosy Females
Male provides a direct benefit to the female or her offspring: nutrition, superior
territory, parental care
There is selection pressure on females to recognize males that are superior
providers
The preference selects for males with the distinctive correlated character
Sexual Selection
Sexual Selection by mate choice
Indirect Benefits of Mate Choice
Male provides no direct benefit to either the female or her offspring but
contributes only his genes
Alleles affecting female mate choice increase or decrease in frequency
depending on the fitness of the females’ offspring. Thus females may benefit
indirectly from their choice of mates
Sexual Selection
Sexual Selection by mate choice
RUNAWAY SEXUAL SELECTION MODEL (SEXY SON HYPOTHESIS)
The evolution of male trait and a female preference, once initiated, becomes a
self-reinforcing or runaway process
Consider haploid males of genotypes T1 (fr t1)
and T2 (fr t2)
T2 has an exaggerated trait (longer tail) that
carries an ecological disadvantage (increasing
the risk of predation)
Females of genotype P2 (fr p2) prefer males of
type P2, whereas P1 females exhibit little
preference
It is assumed that P1 and P2 are selectively
neutral
Sexual Selection
Sexual Selection by mate choice
Although the expression of genes P and T is sexlimited both sexes carry both genes and
transmit them to offspring
Because P2 females and T2 males tend to mate
with each other linkage disequilibrium will
develop
Any increase in the frequency of the male trait
is accompanied by an increase in the frequency
of the female preference through hitchhiking
Sexual Selection
Sexual Selection by mate choice
Because of the genetic correlation between loci, an
increase in t2 is accompanied by an increase in p2: T2
males have more progeny and their daughters tend to
inherit the P2 allele, so P2 also increases in frequency
As P2 increases males have a still greater mating
advantage because they are preferred by more females
Many exaggerated sexually selected traits carry ecological costs for the males that
bear them. Female choice may also carry an ecological cost (ex delayed
reproduction)
Such costs may prevent the runaway process from occurring, or they mat lead to
an equilibrium at which the male trait and the female preference are less extreme
than if there were no cost
Runaway sexual selection of this kind could explain the extraordinary variety of
male ornaments among different species of hummingbirds any many other
animals
Sexual Selection
Sexual Selection by mate choice
GOOD GENES MODEL (HANDICAP HYPOTHESIS)
Because females risk substantial losses of fitness if their offspring do not survive
or reproduce, one could argue that females should evolve to choose males with
high genetic quality, so that their offspring will inherit “good genes” and so have
a superior prospect of survival and reproduction
Stickelback
Fish
Any male trait that is
correlated with genetic quality
(an indicator of good genes)
could be used by females as a
guide to advantageous
matings, so selection would
favor a genetic propensity in
females to choose mates on
this basis
Sexual Selection
Sexual Selection by mate choice
Antagonistic Coevolution
Genes that govern male versus female characters may conflict resulting in
antagonistic coevolution
Such evolution may consist of a protracted “arms race” in which change in male
character is parried or neutralized by evolution of female character, which in turn
selects for change in the male character and so on in a chain reaction
Abalones are externally fertilizing species.
Sperm compete to fertilize eggs
so selection on sperm always favors a greater
ability to penetrate eggs rapidly
Abalone
Haliotis sorenseni
Selection on eggs should favor features that
slow sperm entry or else polyspermy may result
(polyspermy disrupts development)
Coevolution might be the cause of the extraordinarily rapid evolution of the amino acid
sequence of the sperm lysin protein of abalones, a protein released by sperm that bores a
hole through the vitelline envelope surrounding the egg
Sexual Selection
Sexual Selection by mate choice
Chase-away Sexual Selection
Females evolve resistance to male’s
inducements to mate and their resistance selects for features that enable
males to overcome the females’ reluctance
Semen Toxicity
Forced Copulation
Ex Water Striders Males force
females to copulate
Traumatic Insemination
Ex Bed Bug
Males pierce his
mate’s abdominal wall with his genital
structure
Water Strider
Gerris sp
Social Interactions and the Evolution of Cooperation
Explaining how altruism –which by definition reduces personal fitness– can arise by natural
selection is a major problem, and the central theoretical problem of sociobiology
Social Interactions and the Evolution of Cooperation
Darwin’s theory of natural selection is based on individual advantage. Cooperative
interactions seem antithetical to evolution by natural selection and require
explanation
Until 1960’s it was common for biologists to assume that cooperation had evolved
because it benefited the population or species (group selection). The modern study
of cooperation focus on individual selection.
Social Interactions and the Evolution of Cooperation
Prisoner's Dilemma
C
S
Confess:
C
3
1
Silent: S
4
2
Social Interactions and the Evolution of Cooperation
Prisoner's Dilemma
The Prisoner's Dilemma game takes its name from the following scenario:
You and a criminal associate have been busted. Fortunately for you, most of the evidence was
shredded, so you are facing only a year in prison. But the prosecutor wants to nail someone, so he
offers you a deal: if you squeal on your associate –which will result in his getting a five year stretch–
the prosecutor will see that you are set free. Which sounds good, until you learn your associate is being
offered the same deal – which would get you five years
Social Interactions and the Evolution of Cooperation
To cooperate, or not cooperate? This simple question,
expressed in an extremely simple game, is a crucial issue
across a broad range of life
• Why shouldn't a barracuda eat the little fish that
has just cleaned it of parasites
• Fig wasps collectively limit the eggs they lay in fig
trees. But why shouldn't any one fig wasp cheat
and leave a few more eggs than her rivals?
• At the level of human society, why shouldn't each
of the villagers that share a common but finite
resource try to exploit it more than the others?
Yet barracudas, fig wasps, and villagers all cooperate. It
has been a constant problem in evolutionary studies to
explain how such cooperation should evolve, let alone
persist, in a world of self-maximizing egoists
Social Interactions and the Evolution of Cooperation
Explaining how altruism –which by definition reduces personal fitness– can arise by natural
selection is a major problem, and the central theoretical problem of sociobiology
Theories of cooperation and altruism
Cooperation
Direct
Benefits
Enforced
Non
Green
Enforced -beard
Punishment
Reciprocity
Reward
Direct
Indirect
Benefits
Indirect
Kin
Selection
Limited
Kin
Dispersal Discrimination
Social Interactions and the Evolution of Cooperation
DIRECT BENEFITS: NON-ENFORCED
Cooperative behavior often evolves simply because it is advantageous to the
individual
Ex Joining flock or herd
Ex Unrelated helpers and delayed benefit
Pied kingfisher
Ceryle rudis
Social Interactions and the Evolution of Cooperation
DIRECT BENEFITS: ENFORCED: MANIPULATION & PUNISHMENT
A donor may dispense aid to a recipient not because it is adaptive but simply
because the donor is being manipulated or coerced
Ex Cuckoo
Common Cuckoo
Cuculus canorus
Social Interactions and the Evolution of Cooperation
Social Interactions and the Evolution of Cooperation
DIRECT BENEFITS: ENFORCED: RECIPROCITY
It can be advantageous for an individual to help another if the recipient provides
reciprocal aid in the future
Vampire Bats
Desmodus rotundus
Social Interactions and the Evolution of Cooperation
INDIRECT BENEFITS: GREEN-BEARD GENES
Facultative harming greenbeards include the Gp-9 gene of the red fire ant Solenopsis
invicta, which makes carrying workers execute non-carrying queens
Social Interactions and the Evolution of Cooperation
INDIRECT BENEFITS: KIN SELECTION
Kin selection
Selection based on the effect of an allele on both the fitness of
the individual bearing it and the fitness of other individuals that
carry copies of the same allele
For kin selection to operate individuals must dispense benefits more often to kin
than non-kin. This can happen in two ways:
• Many animals can distinguish kin from non-kin
• The population may be structured so that interacting individuals are more
likely to be related than unrelated
Social Interactions and the Evolution of Cooperation
Inclusive Fitness and Kin Selection
Inclusive Fitness
Is the effect of an allele on both the fitness of the individual bearing it (DIRECT
FITNESS) and the fitness of other individuals that carry copies of the same allele
(INDIRECT FITNESS)
Social Interactions and the Evolution of Cooperation
Inclusive Fitness and Kin Selection
Kin selection
Selection based on inclusive fitness
Hamilton’s Rule
An altruistic trait can increase in frequency if the benefit (B) received by the
donor’s relatives weighted by their relatedness (r) to the donor, exceeds the
cost (C) of this trait to the donor’s fitness:
rB>C
Coefficient of Relatedness
Is the fraction of the donor’s genes that are identical by descent with any of
the recipient’s genes
Mother/Offspring
Sibling/Full Sibling
r=½
r=½
Social Interactions and the Evolution of Cooperation
INDIRECT BENEFITS: KIN SELECTION: KIN DISCRIMINATION AND CANNIBALISM
Many species of animals are cannibalistic preying on smaller individuals of the same
species. Many such species discriminate kin from non-kin and are less likely to eat
related individuals
Tadpoles develop into:
• Detritus and plant omnivores
Associate more with their siblings
• Cannibalistic carnivores
Associate more with nonrelatives
Carnivores eat siblings much less
frequently than unrelated
individuals
Spadefoot Toad
Scaphiopus bombifrons
Social Interactions and the Evolution of Cooperation
INDIRECT BENEFITS: KIN SELECTION: COOPERATIVE BREEDING
In many species of animals, young are reared not
only by their parents, but also by other individuals
that are physiologically able to reproduce but do
not. Several factors may explain cooperative
breeding, including kin selection, since in many
species, the helpers aid their parents in rearing
their children
Primary are related
Secondary are unrelated
Pied kingfisher
Ceryle rudis
Meerkats
Social Interactions and the Evolution of Cooperation
SOCIAL INSECTS
Eusocial animals Animals in which nearly or completely sterile individuals (workers)
rear the offspring of reproductive individuals , usually their parents
Known in Naked mole rat, termites, many hymenoptera
Naked Mole Rat
Heterocephalus glaber
Social Interactions and the Evolution of Cooperation
Eusocial hymenoptera are haplodiploid: females develop from fertilized eggs and
are diploid but males develop from unfertilized eggs and are haploid
In a colony with a single, singly mated queen, the inclusive fitness of a female (a
worker) may be greater if she devotes her energy to rearing reproductive sisters
(future queens) than to rearing daughters
Why?
Queen
♀
♂
AB
C
Worker Worker
♂
♂
A
B
♀
♀
AC
BC
Drone
♂
D
Actor
Recipient
Female
Daughter
Female
Son
Male
Daughter
♀
♀
♀
♀
Sister
Sister
AD
CD
BD
CD
Sister
Brother
r
Social Interactions and the Evolution of Cooperation
Eusocial hymenoptera are haplodiploid: females develop from fertilized eggs and
are diploid but males develop from unfertilized eggs and are haploid
In a colony with a single, singly mated queen, the inclusive fitness of a female (a
worker) may be greater if she devotes her energy to rearing reproductive sisters
(future queens) than to rearing daughters
Queen
♀
♂
AB
C
Worker Worker
♂
♂
A
B
♀
♀
AC
BC
Drone
♂
D
Actor
Recipient
r
Female
Daughter
½
Female
Son
½
Male
Daughter
1
♀
♀
♀
♀
Sister
Sister
¾
AD
CD
BD
CD
Sister
Brother
¼
A Genetic Battleground: The Nuclear Family
It would seem that relationships within families should be the epitome of
cooperation, since the parent’s fitness depends on producing surviving offspring.
However, evolutionary biologists have come to understand that these interactions
are pervaded with potential conflict, and that much of the diversity of reproductive
behavior and life histories among organisms stems from the balance between
conflict and cooperation
A Genetic Battleground: The Nuclear Family
Mating Systems and Parental Care
Whether or not one or both of the parents care for offspring varies greatly among
individual species and partly determines the mating system, the pattern of how
many mates individuals have a whether or not they form pair bonds
Providing care increases offspring survival, which enhances the fitness of both
parents. But parental care is also likely to have a cost. It entails risk and it requires
the expenditure of time and energy that the parent might instead allocate to
further reproduction
A Genetic Battleground: The Nuclear Family
Infanticide, abortion and siblicide
Great Tit
Brown Booby
A Genetic Battleground: The Nuclear Family
Parent-offspring Conflict
Parents and offspring typically differ with respect to the optimal level of parental
care. A parent’s investment of energy in caring for one offspring may reduce her
production of other (future) offspring
Production of other offspring increases the inclusive fitness of both the parent and
each current offspring. However, the parent is equally related to all her offspring
(r=0.5), whereas each offspring values parental investment in itself twice as much
as investment in a full sib (r=0.5)
Therefore offspring are expected to try to obtain more resources from a parent
than it is optimal for the parent to give
Intragenomic Conflict
Selfish Genes
Genes that increase in frequency not because they provide an
advantage to the organism that carries them but simply because they have an
advantage in transmission
Genes that promote their own spread at a faster rate than other parts of the
genome, can create a context in which there is selection for genes at other loci to
suppress their effects. When this is the case, a genetic conflict is said to exist
Genomic Imprinting
Genomic imprinting in a broad sense is the asymmetric expression of genes with
different parental origin
Reik and Walter 2001
Genomic Imprinting
Genomic imprinting in a narrow sense is the expression of a gene either when
maternally inherited only (maternally expressed) or when paternally inherited
only (paternally expressed)
Reik and Walter 2001
Genomic Imprinting
86 imprinted genes have been identified but recent results indicate that there
might be up to 824 imprinted genes only in the brain
Gregg et al 2010
data from Gregg et al 2010
Kinship Theory of Genomic Imprinting:
Family Matters
It applies to genes whose phenotype affects the kin of their carrier
Haig 2002
Imprinted genes were first identified
as mediators of embryonic and
placental growth
Moore and Haig 1991, Constancia et al 2004
Formulated in terms of conflict
between maternally and paternally
inherited genes over the allocation of
maternal resources to current embryo
(and/or infant)
Moore and Haig 1991
Constancia et al 2004
Kinship Theory of Genomic Imprinting:
Family Matters
If the carrier is equally related to her target kin via its MI and PI genes, these
genes do not come into conflict over their combined level of expression
Haig 2002, Wilkins and Haig 2003
Monogamy
Mother
Father
Z R
Offspring
Maternally Paternally
Inherited Inherited
Current
Future
Offspring
Offspring
Kinship Theory of Genomic Imprinting:
Family Matters
If the carrier is differentially related to her target kin via its MI and PI genes,
these genes do come into conflict over their combined level of expression
Haig 2002, Wilkins and Haig 2003
Promiscuity
Mother
Z R
Father
ρ
Another
Father
1–ρ
Offspring
Maternally Paternally
Inherited Inherited
Current
Offspring
Future
Offspring
Kinship Theory of Genomic Imprinting:
Family Matters
PI genes are favored to extract more maternal resources than MI genes,
because the cost of increased resource extraction is incurred by maternal sibs
who may not be paternal sibs
Haig 1996, Wilkins and Haig 2003
Promiscuity
Mother
Z R
Father
ρ
Another
Father
1–ρ
Offspring
Maternally Paternally
Inherited Inherited
Current
Offspring
Future
Offspring
Kinship Theory of Genomic Imprinting
If these genes can show expression conditional on their parent of origin, genes
selected for lower level of expression become silent and genes selected for
greater level of expression become expressed at their optimal level: LOUDEST
VOICE PREVAILS PRINCIPLE
Haig 2002
Resource
Enhancer
Kinship Theory of Genomic Imprinting
What is the predicted direction of the imprint for a resource inhibitor?
Kinship Theory of Genomic Imprinting
Resource
Inhibitor
Kinship Theory of Genomic Imprinting
Imprinted genes are found mostly in clusters
What is the predicted offspring size if there is a deletion affecting a cluster and
this is PI?
Kinship Theory of Genomic Imprinting
Male lion x Female tiger
Female lion x Male tiger
Liger
Tigon
900Lbs
400-300Lbs
275Lbs
Growth and Resource Acquisition
PLACENTAL INVASION
The placenta comprises a fetal portion derived from trophoblasts and a
maternal portion derived from the inner layer of the uterine wall
Reduced resistance of placental arteries increments maternal systemic
circulation through the placenta. The greater the blood flow the through the
placenta the greater the transfer of maternal resources to her offspring
Growth and Resource Acquisition
PLACENTAL INVASION
Maternal arteries and placental
trophobalst antagonize over the optimal
level of resistance:
• Maternal arteries become more
convoluted to increase resistance
• Placental trophoblast cells modify
maternal arteries to allow greater
blood flow through the intervillous
space
Growth and Resource Acquisition
PLACENTAL INVASION
Maternal arteries and placental
trophobalst antagonize over the optimal
level of resistance:
• Maternal arteries become more
convoluted to increase resistance
• Placental trophoblast cells modify
maternal arteries to allow greater
blood flow through the intervillous
space
Growth and Resource Acquisition
PLACENTAL INVASION
The greater the penetration of the placenta into the myometrium the greater
the arterial modification and the blood flow.
The paternally expressed IGF2 and expressed in invasive trophoblast cells
influence the extent of placental invasion.
PI genes are expected to favor a greater modification
Growth and Resource Acquisition
BLOOD PRESSURE
The higher the maternal blood pressure the greater the blood flow through the
intervillous space and the transfer of maternal resources to her offspring.
One of the most common complications of pregnancy (fatal in developing
countries) is pregnancy induced hypertension and its extreme form
pre-eclampsia.
Pre-eclampsia can be caused by mutations at one of several loci, at least one of
which is known to be imprinted —the maternally expressed STOX1 gene.
PI genes are expected to favor greater gestational blood pressure than their MI
homolog.
While the exact role of STOX1 remains unclear, the Kinship Theory would predict
that increased expression of STOX1 would reduce maternal blood pressure.
Growth and Resource Acquisition
NUTRIENT CONCENTRATION IN MATERNAL CIRCULATION
After each meal, maternal insulin prompts the uptake of glucose by maternal
cells. The longer the glucose remains in the maternal circulation the greater the
transfer of maternal resources.
During pregnancy, the placenta antagonizes the action of maternal insulin by
secreting human placental lactogen (hPL) into the mother’s system. hPL
generates resistance to insulin in the maternal cells, thereby elevating the level
of glucose in the maternal circulation.
This manipulation may be ultimately the cause of gestational diabetes, which
occurs late in pregnancy, but generally resolves quickly following delivery.
Paternally expressed PLAGL and maternally expressed LOT1, HYMA1 imprinted
genes have been linked to gestational diabetes.
PI genes are expected to favor greater resistance to insuline than it MI homolog.
Post-Natal Behaviour
After birth, mammals continue to rely heavily on maternal resources (breast milk
and supplemental food), although they are no longer transmitted by means of the
placenta. The conflict between the PI and MI alleles shifts primarily into the
behavioral arena. Genes expressed in the brain will be under selection to
maximize their inclusive fitness, just as they were during pregnancy.
Post-Natal Behaviour
PRADER-WILLI AND ANGELMAN SYNDROMES
Complete Deletion
Ch 15
Ch 15q11-13
Ch 15q11-13
Complete
Ch 15
Wild
Type
Angelman
Syndrome
Prader-Willi
Syndrome
Lethal
Deletion
Ch 15q11-13
• AS is associated with enhanced activity,
prolonged but poorly coordinated suckling
and bouts of laughter among others
• Before weaning, PWS is associated with
reduced activity, poor suckling, weak cry
and sleepiness. After weaning, the child
develops an insatiable appetite and
becomes obese.
Post-Natal Behaviour
PRADER-WILLI AND ANGELMAN SYNDROMES
The Kinship Theory would predict that:
• The increase in the duration of suckling found
in AS results from the loss of MI alleles that
have been selected to reduce the demand for
maternal resources.
• PWS is associated with poor food uptake prior
to weaning and ravenous food uptake after.
o The pre-weaning phenotype may result
from the loss of PI alleles that been
selected to increase the demand of
maternal resources
o The post-weaning phenotype may result
from an increment in the relative
contribution of paternal resources after
weaning
Complete Deletion
Ch 15
Ch 15q11-13
Expression
of RE only
Complete
Ch 15
Angelman
Syndrome
Expression
Deletion
of RI Only
Ch 15q11-13
Prader-Willi
Syndrome
Post-Natal Behaviour
MATERNAL CARE
Peg1 and Peg3, show paternal-specific expression in the brain of adult mice. These
genes appear to affect the quality of care that mothers provide to their offspring, as
knockouts of these genes result in defects in maternal behaviors of nest building,
pup retrieval and placentophagy.
Although the phenotype involves the provisioning of maternal resources to
offspring, the conflict in this case is between the mother’s two alleles, rather than
those of the offspring. The source of this conflict is not obvious, however, since
each of the mother’s alleles has an equal chance of being passed to each of her
offspring. However, if there is some inbreeding in the population, the offspring
could inherit an allele from the father that is identical to one of the mother’s
alleles.
Under several plausible patterns of inbreeding, the allele inherited from the father
is more likely to be identical to the mother’s paternally derived allele than to her
maternally derived allele. For example, if the mother mates with her own father
(i.e., the father and maternal grandfather are the same individual), the mother’s
paternally derived allele will be more closely related to her own offspring than her
maternally derived allele will.