Title: Adaptation to environmental gradients: A simulation and some observations on Littorina saxatilis
1Adaptation to environmental gradientsA
simulation and some observations on Littorina
saxatilis
- Roger ButlinAnimal and Plant SciencesThe
University of Sheffield
2Adaptation to environmental gradients
- Two outstanding questions
- What limits spread?
- Can local adaptation lead to speciation?
3Outline
- 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
4Some range margins in Britain
Cirsium eriophorum
Gentianella campestris
Pinguicula vulgaris
Trollius europaeus
5Patchiness is on a range of scalesCD Thomas and
coworkers
Plebejus argus
6Central to marginal gene flow
Asymmetric gene flow
Tolerance limit
7Kirkpatrick and Barton 1997
From Case Taper 2000
8Kirkpatrick and Barton 1997
Rate of change of environment
Bbs/(r(2Vs)0.5)
Genetic potential for adaptation AG/(2Vsr)
9Barton 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
10An 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
11Typical outcomes
Spread dispersal 200 mating 150
No spread dispersal 700 mating 150
Extinct
12Expected 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.
13Variance at centre and margin
Phenotype
Variance
Density
14Effect of carrying capacity
15Population density
cc25
cc12
cc5
16Mating area effect
17Allee effect at margins
18Contribution of Allee effect
19Biased gene flow at high mating distance
Mating distance600
Enhances migrational load in marginal populations
20Ve 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?)
21Simulation 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?