Review on genetic vs. plastic adaptation to climate change
Possible structure (potentially as list of questions)
Introduction
- What can theory contribute to the study of adaptation to climate change?
- Identify important parameters
- Make rough predictions about quantitative change
- Suggest measures and scalings
- What theory cannot do
- Predict the ratio of genetic vs. plastic responses
- Make exact quantitative predictions
- Scope of this paper
- Phenotypic evolution of quantitative change
- Simple selective scenarios
- Focus on rates
Methods
- How should evolutionary change be measured?
- Darwins, haldanes, haldane numerators
- mean- vs. variance standardization (Herford et al. 2004)
- extrapolation to per-generation rates (Gingerich)
- How to model phenotypic evolution?
- Quantitative genetics (adaptation from standing genetic variation)
- population genetics (adaptation by single large mutations)
- adaptive walks (new mutations only)
- optimality, game theory (not needed for simple scenarios considered here; relevant for evolution of plasticity)
- adaptive dynamics (for evolution of plasticity, eco-evolutionary feedbacks)
- Which scenarios of environmental change have been considered?
- sudden change,
- moving optimum,
- stochastic fluctuations
- increased variability
- range shifts????
What is the genetic basis of adaptation?
- Standing variation vs. new mutations
- Small or large mutation
- How does the genetic basis affect adaptation?
(Difficult to discuss details here; maybe just use as announcement, or combine with modeling approaches)
Basic models
- Sudden change, quantitative genetic
- Sudden change, major locus
- linearly moving optimum, quantitative genetic
- linearly moving optimum, major locus
Univariate models
- Rate of adaptation
- From new mutations: fixation probability (Haldane, Kimura, Gomulkiewicz and Kirkpatrick, Orr and Uncless, Uecker and Hermisson)
- From standing variation (quantitative genetic models): Lande's equation
- Additive genetic variance (under mutation-selection balance and during evolution); when will additive variance be exhausted?
- Selection gradients
- Evolutionary rescue
- from standing variation or new mutations
- in models with sudden change
- in models with moving optimum
- critical rates of environmental change
- phenotype vs. fitness
Multivariate models
- How to model multivariate evolution?
- Multivariate Lande's/breeders' equation
- Fisher's geometric model
- Pleiotropic side effects
- How many traits? (Organismal complexity)
- What are the effects of multivariate mutation and selection?
- G-matrix, M-matrix
- Evolution of G-matrix
- Genetic line of least resistance
- multivariate constraints
- evolution of mean fitness
- Evolvability
Plasticity
- How to model plasticity?
- How plastic are organisms?
- How does plasticity interact with genetic evolution?
- Does plasticity evolve during adaptation?
- How does plasticity contribute to evolutionary rescue?
Open questions
- Evolutionary change in a community context
- Effects of plasticity (trait-mediated indirect effects etc.)
- Eco-evolutionary dynamics
- Ecological constraints on adaptation (niche conservatism)
List of questions
Introduction
- What can theory contribute to the study of adaptation to climate change?
- How to measure (rates of) adaptation?
- What is evolutionary rescue?
- Which modeling approaches have been used?
Genetic adaptation: univariate case
- Basic scenarios: sudden change and moving optimum, adaptation from quantitative variation or a single major mutation
- How fast can genetic adaptation be?
- What is the genetic basis of adaptation, and how does genetic variation evolve?
- Adaptation in time and space
Genetic adaptation: multivariate case
- What are the effects of multivariate selection and genetic correlations?
- How does the G-matrix evolve?
- What determines evolvability?
Plasticity
- How can plasticity be modeled?
- How and when does plasticity evolve?
- Does plasticity facilitate genetic adaptation?
Responses at the community level
Questions for empiricists
In all cases, the answer may be quantitative, or may contain a list of factors that influence the result.
- Overall questions:
- How fast can adaptation happen?
- Plastic or genetic adaptation?
- Evolutionary rescue?
- How much due to plasticity? (no general answers)
- Adaptation from standing variation or new mutations?
- Small or large mutations?
- How much standing genetic variation?
- What happens to genetic variance during adaptation?
- What constrains adaptation?
- What determined evolvability?
- Maximal rate of genetic adaptation?
- Evolutionary rescue due to genetic adaptation?
- How much plasticity?
- Will plasticity evolve?
- Can plasticity enhance genetic adaptation?
- Evolutionary rescue with plasticity?
- What happens at the community level?
Questions in Barrett and Hendry (2012)
How important is genetic (as opposed to plastic) change?
- We might ask: What is possible with genetic change only?
Will plasticity evolve?
- Most likely yes:-)
- Approaches: Lande 2009, earlier models from 1990s, Draghi and Whitlock
- Baldwin effect etc.
Is evolution fast enough
- How fast without plasticity?
- Factors determining speed:
- Genetic variance (large literature here)
- Selection gradient
- Multivariate constraints
- Evolvability, complexity etc.
- Evolutionary rescue
- critical rates: explain
- Explain Lynch and Lande (1993)
- Key factors: selection gradient vs. mean fitness
- Strong selection is a good thing with a moving optimum
- additional factors: demographic and environmental stochasticity
Standing variation vs. new mutations?
- Different theoretical approaches/traditions
- Quantitative genetics vs. adaptive walks
- Some results from quantitative genetics (Hill…)
- Open questions
How many genes and what effect
- Lots of recent interest in models of adaptive walks (from new mutations only)
- Kopp and Hermisson 2009b: at least in univariate case, adaptive walk predictions are good approximations to quantitative genetic model
Constraints: limited genetic variation
- models on maintenance of genetic variation
Constraints: Trait correlations
- multivariate constraints
- Fisher's model etc.
Constraints: Ultimate constraints
- trade-offs?
What can one say abouts phenotypic rates of adaptation from sgv?
Univariate case
- Starting point: Lande's equation: selection gradient and additive variance
- Lot's of literature on additive variance
- Selection gradient vs. mean fitness: depends on fitness function
- double exponential fitness function: selection gradient constant
- Problem: How to deal with phenotypic variance and sampling error? For an observed change to be significant, the difference in haldanes must be <latex>(\bar x - \bar y)/\sigma_p > 1.96\sqrt(2/n)</latex>; for n = 100, this is 0.087.
- check out Lande 1976, Hendry and Kinnison 1999, Gingerich 2009 for this
- essentially dividing the Lande equation by sigma_p leads to standardized selection gradients, discussed and critized in Herford et al. 2004
Multivariate case
- Multivariate Lande's equation
- critized by Morrisey et al. 2010
- Multivariate constraints: Walsh and Blows 2009
Narrative
What happens when a populations experiences environmental change, and which theoretical problems do we encounter along the way?
- Before the change: maintenance of genetic variation (mutation-selection balance, fluctuating selection …)
- Different kinds of environmental change
- Adaptation from standing genetic variation
- Adaptation from new mutations (unlikely)
- Evolutionary rescue?
- Plasticity
- Which factors favor adaptation: genetic variation, plasticity, evolvability, modularity, lack of complexity