Adaptation to environmental gradients: A simulation and some observations on Littorina saxatilis - PowerPoint PPT Presentation

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Adaptation to environmental gradients: A simulation and some observations on Littorina saxatilis

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Empirical progress with the periwinkle, Littorina saxatilis ... Cirsium eriophorum. Gentianella campestris. Pinguicula vulgaris. Trollius europaeus. 5 ... – PowerPoint PPT presentation

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Title: Adaptation to environmental gradients: A simulation and some observations on Littorina saxatilis


1
Adaptation to environmental gradientsA
simulation and some observations on Littorina
saxatilis
  • Roger ButlinAnimal and Plant SciencesThe
    University of Sheffield

2
Adaptation to environmental gradients
  • Two outstanding questions
  • What limits spread?
  • Can local adaptation lead to speciation?

3
Outline
  • An individual-based simulation
  • Masakado Kawata, Tohoku University
  • Jon Bridle, Institute of Zoology
  • Empirical progress with the periwinkle, Littorina
    saxatilis
  • John Grahame and Henry Wood, University of Leeds
  • First a bit about the nature of margins

4
Some range margins in Britain
Cirsium eriophorum
Gentianella campestris
Pinguicula vulgaris
Trollius europaeus
5
Patchiness is on a range of scalesCD Thomas and
coworkers
Plebejus argus
6
Central to marginal gene flow
Asymmetric gene flow
Tolerance limit
7
Kirkpatrick and Barton 1997
From Case Taper 2000
8
Kirkpatrick and Barton 1997
Rate of change of environment
Bbs/(r(2Vs)0.5)
Genetic potential for adaptation AG/(2Vsr)
9
Barton 2001
  • Genetic variance imposes costs in centre of range
    and benefits at margins
  • If variance is allowed to evolve, adaptation to
    arbitrarily steep gradients is possible
  • Therefore, something is missing

10
An individual-based modelderived from Kawata 2002
Habitat8000x1000
Environmentalgradient
Spatial parameters dispersal distance,
interaction distance, mating distance
stabilizing selection
Fitness W 2 r (1 - N/K) - (Ux-z)2/2Vs
phenotype of female
intrinsic rate of increase
optimum at x
equilibrium density
competitors
11
Typical outcomes
Spread dispersal 200 mating 150
No spread dispersal 700 mating 150
Extinct
12
Expected clines etc
Total dispersal 100 Mating distance 150 Carrying
capacity 25
Width and variance closer to expectation, and
effect of LD increases,as clines overlapmore
with higherdispersal.
13
Variance at centre and margin
Phenotype
Variance
Density
14
Effect of carrying capacity
15
Population density
cc25
cc12
cc5
16
Mating area effect
17
Allee effect at margins
18
Contribution of Allee effect
19
Biased gene flow at high mating distance
Mating distance600
Enhances migrational load in marginal populations
20
Ve and mutation
  • Adding environmental variance
  • No effect on central density (depends on G not
    h2, Kirkpatrick and Barton 1997)
  • Critical dispersal value for spread
    increases(depends on h2 and intensity of
    selection (Vp/Vs), KB97)
  • Increasing mutation rate
  • Little effect on critical dispersal
    value(because effect on G small compared to
    dispersal)
  • Does increase upper critical mating
    distance(because of biased gene flow after
    selection?)

21
Simulation summary
  • Finite population size does influence ability to
    adapt to an environmental gradient
  • Mating/gamete dispersal as well as offspring
    dispersal need to be considered
  • Narrow parameter space for limited range
  • Not critical because of steepening gradients at
    boundaries?
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