Maternal effects and evolution

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Maternal effects and evolution
Kate LessellsNetherlands Institute of Ecology
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1) Maternal effects
What is a maternal effect?
Maternal effects are broadly defined as
phenotypic variation in offspring that is a
consequence of the mothers phenotype rather than
the genetic constitution of the offspring (Roff
1998)
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1) Maternal effects
What is a maternal effect?
Maternal effects are broadly defined as
phenotypic variation in offspring that is a
consequence of the mothers phenotype rather than
the genetic constitution of the offspring (Roff
1998)
Examples
Coenagrion puella mothers with higher parasite
loads produce larger larvae(Rolff 1999)
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1) Maternal effects
What is a maternal effect?
Maternal effects are broadly defined as
phenotypic variation in offspring that is a
consequence of the mothers phenotype rather than
the genetic constitution of the offspring (Roff
1998)
Examples
Onthophagus taurus mothers mated to large-horned
males provide more resources to their
young(Kotiaho et al. 2003)
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1) Maternal effects
What is a maternal effect?
Maternal effects are broadly defined as
phenotypic variation in offspring that is a
consequence of the mothers phenotype rather than
the genetic constitution of the offspring (Roff
1998)
Examples
Nest orientation by chestnut-collared longspurs
affects chick growth(Lloyd Martin 2004)
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1) Maternal effects
NSF/NSERC/ESF workshop Maternal effects NSF
network Integrating ecology and endocrinology in
avian reproduction
Maternal effects in birds involving hormones
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1) Maternal effects
Maternal effects in birds involving hormones
Maternal effects involve the mother doing
something to the offspring i.e. some maternal
behaviour
1) Hormones control the maternal behaviour
e.g. hormones control provisioning rates
Evolutionary interest Hormones might affect the
outcome of evolution if they cause (rather than
just modulating) trade-offs
2) Hormones are the maternal behaviour e.g.
maternal yolk hormones
Evolutionary interest Understanding the action
of the hormones in the light of evolutionary
conflicts of interest
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1) Maternal effects
Maternal genes
Maternal environment
Maternal phenotype
Offspring phenotype
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1) Maternal effects
Maternal genes
Maternal environment
Maternal phenotype
StateInformation
Behaviour
Offspring phenotype
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1) Maternal effects
Maternal genes
Maternal environment
Maternal phenotype
Effects of maternal environment- long-term
e.g. size- short-term e.g. condition
StateInformation
Behaviour
Offspring phenotype
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1) Maternal effects
Maternal genes
Maternal environment
Maternal phenotype
The maternal environment can also act as a cue,
predicting the environment of the offspring
StateInformation
Behaviour
Offspring phenotype
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1) Maternal effects
Maternal genes
Maternal environment
Maternal phenotype
Female does something that has an effect on the
offsprings phenotype
StateInformation
Behaviour
Offspring phenotype
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1) Maternal effects
Maternal genes
Maternal environment
Decision-making process
Maternal phenotype
- subject to selection, so expect the variation
in offspring phenotype that the maternal effect
brings about to be adaptive
StateInformation
Behaviour
Adaptive transgenerational phenotypic
plasticity(Mousseau Fox 1998)
Offspring phenotype
- enables parents to translate their experience
into adaptive variation in their offspring
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2) Adaptive transgenerational phenotypic
plasticity
Adaptive transgenerational phenotypic plasticity
e.g. Rana arvalis mother modifies jelly of her
eggs in relation to pH to maximise embryo
survival(Räsänen et al. 2003)
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2) Adaptive transgenerational phenotypic
plasticity
Adaptive transgenerational phenotypic plasticity
Maternal behaviour - and hence
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2) Adaptive transgenerational phenotypic
plasticity
Adaptive transgenerational phenotypic plasticity
Transgenerational reaction norm
Maternal behaviour - and hence
Offspring phenotype
Maternal environment
How to we determine what the optimal behaviour
would be in each environment? classical
behavioural ecology approach consider the costs
and benefits
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2) Adaptive transgenerational phenotypic
plasticity
What maternal behaviour and hence offspring
phenotype maximises mothers fitness?
Mothers fitness fitness through current
offspring current fitness - Wc fitness
through future offspring future fitness - Wf
Each of these components of fitness can be
further split into Benefit through
current/future offspring Bc/Bf Cost
through current/future offspring Cc/Cf
Mothers fitness Wc Wf
(Bc Cc) (Bf Cf)
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2) Adaptive transgenerational phenotypic
plasticity
Mothers fitness Wc Wf
(Bc Cc) (Bf Cf)
Parental care
No future costs or benefits
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2) Adaptive transgenerational phenotypic
plasticity
Mothers fitness Wc Wf
(Bc Cc) (Bf Cf)
Current fitness
Mothers fitness
Future fitness
More generally
? Need to take into account all costs and
benefits to current and future fitness to
understand adaptive maternal effects- so must
measure these (experimentally)- need to know if
effects on mother are divorced from effects on
offspring (yolk hormones)
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2) Adaptive transgenerational phenotypic
plasticity
By repeating the analysis of costs and benefits
in each possible environment, we can predict
optimal maternal behaviour in each environment-
build up the optimal transgenerational reaction
norm
Maternal behaviour - and hence
Offspring phenotype
Maternal environment
So is that it?
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3) Evolutionary conflicts of interest
Evolutionary conflicts of interest
Family members tend to be related but apart
from identical twins and asexual clones are
never completely related
As a result there are evolutionary conflicts of
interest what is best evolutionarily for one
individual is not best evolutionarily for another
individual
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3) Evolutionary conflicts of interest
Evolutionary conflicts of interest
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3) Evolutionary conflicts of interest
So how are such conflicts of interest resolved?
Ever-increasing exaggeration of need by offspring
prevented by costs (energetic, predation) -
Parent feeds its optimal amount- But fitness is
reduced by costs of begging
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3) Evolutionary conflicts of interest
? Rules will/may evolve Parental rule how
much to feed in relation to begging Chick
rule how much to beg in relation to hunger
? Selection between rules is reciprocal
Lying by chicks selects parents to downplay
response Downplaying by parents selects
chicks to lie - Downplaying maybe selective
if parents can predict when they will be
lied to
When signalling occurs between two individuals
with an evolutionary conflict of interest, we
should ask the questions- why should the
receiver pay any attention to the signal?- can
the signaller get away with lying?
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3) Evolutionary conflicts of interest
Maternal yolk hormones and evolutionary conflicts
of interest
Do evolutionary conflicts of interest make some
of our explanations for yolk hormones difficult
or untenable? Are yolk hormones a resource or a
signal?
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3) Evolutionary conflicts of interest
Could yolk hormones be a resource?- by
resource mean that yolk hormones are limiting
- have a direct positive effect on offspring
fitness - are costly to mother to produce
Unlike begging, no means for chicks to demand
more- mother could impose her own optimal
distribution between eggs- could be an
evolutionarily stable solution if yolk T is a
resource
? But how do they act as a resource? Why are they
limiting?
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3) Evolutionary conflicts of interest
Could yolk hormones be a signal?- by signal
mean that yolk hormones carry information -
chicks can choose how they react to that
information - not (necessarily) costly to
mother to produce
If there are no costs or benefits to future
fitness, the mothers optimum is the same as the
chicks optimum- i.e. there is no
parent-offspring conflict - could be an
evolutionarily stable solution if yolk T is a
signal
BUT
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3) Evolutionary conflicts of interest
But 1) If parent is signalling availability of
food to feed young- Chicks will increase food
demand in response to yolk T- Thus there will be
a cost to future fitness, and hence
parent-offspring conflict - Parent can avoid the
costs of conflict by adjusting its response to
begging, rather than signalling to chick to
adjust its begging in response to hunger
- Parent should only signal current food
availability if chick benefits from knowing in
advance how much it will be fed e.g. to adjust
its target growth trajectory- For similar
reasons, parents may signal expected feeding
conditions for offspring once independent may
also give away feeding conditions for
provisioning parent if the two sets of feeding
conditions are similar
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3) Evolutionary conflicts of interest
But 2) If there is more than one chick- So
long as costs and benefits of response act
individually on each chick, the offsprings and
mothers optima are the same signalling is
evolutionarily stable- e.g. benefit of response
is aggression reducing individual risk of
kleptoparastism, and cost of response is
immunosupression
- But it will rarely be true that costs and
benefits act individually- e.g.1 benefit of
response is aggression used to defend a brood
territory against kleptoparasitism by other
chicks - will then be parent-offspring
conflict over aggressiveness of chicks- e.g.2
parent might be signalling position in the laying
sequence - will be parent-offspring conflict
over how competitive each chick should be
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3) Evolutionary conflicts of interest
But 2) If there is more than one chick
If there is parent-offspring conflict (as in the
examples), the chicks will modify their behaviour
in response to the signal in a way that maximises
their own fitness, not the mothers- expect the
mother to lie and the chicks to downplay
the signal- likely to be resolved in a way
analagous to begging - there will be
unavoidable costs associated with the signal
(either to mother or offspring) - the
chicks will win, i.e. have their, not the
mothers optimal behaviour
? If yolk hormones are a signalling system, they
are likely to carry unavoidable costs? Usage of
information signalled should be consistent with
the chicks not the parents optimum- Rather
paradoxically, the individual who has the
information initially (the chicks know their
hunger and signal it by begging the mother knows
the environmental conditions/laying order and
signals it by yolk hormones) is not the one who
achieves its optimum!
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3) Evolutionary conflicts of interest
Could yolk hormones be a way for females to win
in sexual conflict?- in essence, females might
get the chicks to lie to the father about how
hungry they are- e.g. in several species mothers
put more androgen in eggs when mated to one
year-old males
- but father is expected to downplay this lying,
in the same way that the mother would if the
chicks lied to her as a result of
parent-offspring conflict- similarly, fathers
are expected to selectively downplay if they can
predict when the mother would selectively make
the chicks lie (as they would if the mother uses
a paternal characteristic, such as age, to decide
when to make the chicks lie)- therefore seems
unlikely that females might manage to manipulate
the male in this way
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4) Conclusions
Conclusions ? Maternal effects can be
interpreted as adaptive transgenerational
phenotypic plasticity that maximises the mothers
fitness ? However, care must be taken when there
are evolutionary conflicts of interest, because
the transgenerational reaction norm that
maximises the mothers fitness will not maximise
the chicks or fathers fitness- if the mother
is providing a resource, she may be able to
impose her own optimum- if she is signalling
information, it may well be the chicks that can
impose their optimum