Download Interacting phenotypes and conservation genetics

Evolution of interacting phenotypes
Interacting phenotypes occur whenever „[...] interactions
among individuals help determine the phenotype“ (Moore
et al. 1997)
Interacting phenotypes: theory
Social environment
Focal individual
ψ
IGE
IEE
Ψ: interaction coefficient
IGE: indirect genetic effect
IEE: indirect environmental effect
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Interacting phenotypes: theory
Derivation of variance components
a) Traditional phenotype
Random (stochastic)
environmental deviation
zi = ai + ei
„Take the covariance“ for trait i
zi = ai + ei
Cov(ai,zi)=cov(breeding value, phenotype)
cov(ai , zi )=
cov(ai , ai + ei ) = ai + ai ei
2
0
e
Additive
genetic
variance
Genotype X
environment
covariance
Interacting phenotypes: theory
Derivation of variance components
a) Traditional phenotype
VP ,i = Gii + cov(a, e)
Positive genotype x environment covariance
(breeding value and environmental value for the trait point in same direction)
→
More than the additive genetic component in the phenotypic variance
is exposed to selection. Heritability estimates inflated
Negative genotype x environment covariance
→
Less than the additive genetic component in the phenotypic variance
is exposed to selection. Heritability estimates deflated
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Interacting phenotypes: theory
Derivation of variance components
a) Interacting phenotype (exemplified by maternal effect)
Non-random maternal
environmental deviation
zi = ai + ei
generation
„Adaptations involving maternal effects are different from „normal“ traits in that the genes underlying their
expression are contained within the maternal generation while the phenotypic variation on which natrual
selection may act is expressed by the offspring“ (Mousseau and Fox, 1998)
t-1
eo(t)=mzp(t-1)
P
r
t
O
ao,t
m: maternal effect coefficient
zo (t ) = ao (t ) + eo ( t ) → eo ( t ) = mz p ( t −1)
z p ( t −1) = a p ( t −1) + e p ( t −1)
zo ( t ) = ao ( t ) + m(a p ( t −1) + e p (t −1) ) =
e
0
= ao + rma p + me p
Interacting phenotypes: theory
Derivation of variance components
a) Interacting phenotype (exemplified by maternal effect)
„Take the covariance“ for trait i
Cov(ai,zi)=cov(breeding value, phenotype)
Let‘s assume no genotype X environment covariance
cov(ao + rma p , ao + ma p ) =
= ao + (1 + r )ao ma p + rm 2 a p
2
2
= Goo + (1 + r )mGop + rm 2G pp
Direct Genetic Effect (DGE)
Variance
Direct-indirect
covariance
Indirect Genetic Effect (IGE)
Variance
Kirkpatrick and Lande 1989; Cheverud and Moore (1994)
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Interacting phenotypes: theory
Effects of maternal effects on expressed genetic variance and
evolutionary change
1. Increased (or decreased) expressed total genetic variance
(depending on sign of m)
2. After selection, the environment provided by the parent still
reflects the selection in previous generation → environmental
effect on phenotype of offspring of current generation (timelag)
[
]
Δzo = Goo + (1 + r )mGop + rm 2G pp β o
m is the „maternal effect coefficient“ determining the sign and strength of effect of a maternal
phenotype on the offspring phenotype (independent of genetically inherited influences). In general
interacting phenotype theory, ψ is the „interaction coefficient“ determining the strength of effects of the
social environment of phenotypic expression of a focal individual.
Evolutionary consequence of maternal effects
(directional selection on offspring body size with a positive effect of
maternal environment on growth)
β=0.2
β=0.0
Maternal effect
Traditional trait
(R=h2S)
Kirkpatrick and Lande, 1989
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Interacting phenotypes: experiments
Adaptive maternal effect
Gryllus pennsylvanicus
Hogna helluo
Storm & Lima, 2010
If induced by the environment, maternal effects constitute a form of transgenerational phenotypic plasticity.
If the phenotypic effect on the induced maternal effect in the offspring enhances offspring fitness, it is an
adaptive maternal effect. The effect of female cricket (Gryllus pennsylvanicus) exposure to odours of a
predator (wolf spider; Hognal helluo) on offspring antipredator behaviour and survival under threat of
predation is a recent example. However, the maternal effect itself can be heritable, generating IGE‘s
Interacting phenotypes: experiments
Adaptive maternal effect
Passer domestiduc
(Haussperling)
In many bird species, females deposit
androgens into the eggs. Studies on
different species showed that the quantity
of transferred hormones is partly induced
by social and environmental factors
during egg production (e.g., coloniality,
food availability)
Partecke & Schwabl, 2008
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Interacting phenotypes: experiments
Adaptive maternal effect
Ficedula albicollis
(Halsbandschnäpper)
But it has recently also been shown that
the amount of androgens females deposit
in the eggs has a heritable components.
Thus, the offspring phenotype affected by
the maternal androgens are partly
determined by IGE‘s.
Tschirren et al., 2010
Conservation Genetics
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Conservation Genetics
Central Questions
1. What is the unit of group to be conserved (what is an ESU
(an „evolutionarily significant unit“)? The population, subspecies, or species? When are two groups genetically
distinct enough to warant protection of each?
2. How do genetic factors, especially random genetic drift,
inbreeding depression, and mutation, directly affect current
population viability and extinction risk?
3. How much genetic variation is available in endangered and
threatened species for adaptation to future environmental
change?
4. What are the targets of selection humans (as agents of
selection) affect most? How strong is selection exerted by
humans? An what are the prospects that the target of
selection can adapt to the human-induced selection?
Conservation Genetics
Defining ESU‘s
Although controversial, the following criteria are central to
defining ESU‘s:
1. Current geographic separation
2. Neutral genetic differentiation among ESU‘s caused by
past restriction of gene flow
3. Locally adapted phenotypic traits caused by differences
in selection
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Conservation Genetics
Extinction Risk
Local Adaptation
Judgement of Extinction risk versus local
adaptation of ESU‘s is critical to regulate human
intervention. There are genetic and ecological
factors affecting both extinction risk and the scope
for local adaptation.
From previous chapters we know that adaptation is
more likely in large populations with large additive
genetic variance. Small populations tend to harbour
less genetic variance due to inbreeding and drift.
Genetic factors affecting extinction risk
Inbreeding and small effective population size
Inbreeding
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Genetic factors affecting extinction risk
Inbreeding and small effective population size
Effective population size
N=12, Ne=12: 16 Populations
constructed from unrelated
individuals
N=12, Ne=3: 16 Populations
constructed from three fullsibling families
Conservation Genetics
Va, Ne, Na, S
Va, Ne, Na, S
Va, Ne, Na, S
Va, Ne, Na, S
Va, Ne, Na, S
Gene flow
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Genetic factors affecting extinction risk
Inbreeding and small effective population size
Genetic rescue in
adders (Vipera berus)
To protect isolated populations on the
verge of extinction, gene-flow may be
artificially managed by introducing
individuals from large populations with
substantial genetic variation. However, if
populations differ not only due to drift, but
due to local adaptation, such introduction
may be counterproductive leading to
outbreeding depression. If local
adaptation is important, introduction
represents gene-flow of less fit genotypes
for the local ecological conditions.
Resistance to Pesticides and Antibiotics
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Conservation genetics
Concluding remarks
• Humans alter evolutionary dynamics of many species by
affecting gene flow, acting as selective agent and by subdividing populations
• Conservation biology has the difficult task of maximizing the
„longevity“ of ESU‘s given these impacts
• For feasibility, past research mostly relied on neutral genetic
markers in an attempt to estimate extinction risk, heritability,
population differentiation (Fst) and gene-flow. But the
correlations with the corresponding direct estimates are weak
(not surprisingly)
• Evolutionary change depends on an interaction between
strength of selection and the amount of additive variance in a
population. The stronger the selection from human activity, the
larger the variance required to allow a population to adapt.
Often, there is little knowledge of heritable variation in
populations at risk of extinction
General conclusions
• Most phenotypes are continuous, and have a multigenetic basis
• Mendelian inheritance translates quite easily to continuous
variation
• Two covariances are in the center of the theory of phenotypic
evolution: the covariance of phenotype and genotype
(inheritance), and the covariance of fitness and phenotype
(selection)
• Both covariances need to be studied experimentally to
understand the evolution of a system
• The covariances can have a complex biological basis, including
direct genetic, plastic, environmental and indirect genetic
effects
• Because in conservation biology, we try to „manage“
evolutionary processes, quantitative genetics is required when
attempting to predict likelihood of adaptation versus extinction
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