1. Partitioning Phenotypic Variability:
A Second View of Heritability (h2)
VP = VG + Ve
VP – Phenotypic variation
VG – Genetic variation
Ve – Unexplained variation

2. Partitioning Phenotypic Variability:
A Second View of Heritability (h2)
h2 = VG / VP

3. Partitioning Phenotypic Variability:
A More Complete View
Vp = VG + VE + VGxE + Cov(G,E) + Ve
VE – Variation due to environmental factors: plastic response
VGxE – Variation due to an interaction between genotype and the environment that influences phenotype

4. Genotype by Environment Interactions
Response by a single
genotype

5. Genotype by Environment Interactions
Vg in high light
Vg in low light

6. Genotype by Environment InteractionsVE

7. Genotype by Environment Interactions
VGxE – Degree to which lines are not parallel

8. Partitioning Phenotypic Variability:
A More Complete View
Vp = VG + VE + VGxE + Cov(G,E) + Ve
Cov(G,E) – non-random association between genetic makeup and local environmental conditions

9. Sources of Genetic Variation
Factors increasing variation
Mutation
10-8 to mutations per base pair per generation
10-5 to 10-7 mutations per gene per generation
One individual out of 10 per generation

10. Sources of Genetic Variation
Factors increasing variation
Mutation
Migration
Population #1
Population #2
Pollen
Seeds

11. Sources of Genetic Variation
Factors decreasing variation
Natural selection
Genetic drift in small populations (<1000)
Loss of a allele
Small population
Large population
p = frequency (allele A)
q = frequency (allele a)
p + q = 1
Loss of A allele

12. Evidence of Selection in Natural Plant Populations

13. Selection Among Populations

14. The Common Garden Experiments of Clauson, Keck and Heiesy (1948)

15. Differences in phenotype across a gradient: Yarrow (Achiella spp) as an example

16. What is the source of variation?
Different species – genetic variation?
Same species – phenotypic plasticity?

17. Common Garden Experiment
Step #1: Obtain Plants from Source Populations
Stanford – 100’
Timberline – 10,000’
Mather – 4600’

18. Clones (e.g., piece of root)
Common Garden Experiment
Step #2: Produce Clones
Source Plant
Clones (e.g., piece of root)
Location #1
Location #2

19. Clones (e.g., piece of root)
Common Garden Experiment
Step #3: Plant clones in common gardens
Source Plant
Clones (e.g., piece of root)
Common Gardens
Location #1
Location #1
Location #2
Location #2

20. Stanford Common Garden

21. Mather Common Garden

22. Timberline Common Garden

23. Interpretation of Results: Pure Plastic Response
Source Plant
Clones
Common Gardens ?
Location #1
Location #1 ?
Location #2
Location #2

24. Interpretation of Results: Pure Genetic Response
Source Plant
Clones
Common Gardens ?
Location #1
Location #1 ?
Location #2
Location #2

25. Experimental Outcome: Growth of Mather Achiella Clones
Genetic response
Plastic response

26. Potentilla glandulosa
A Second Example
Potentilla glandulosa
Copyright © by Jane Strong and Tom Chester

27. Lowland Plant Lowland Ecotype
©Brother Alfred Brousseau, St. Mary's College

28. Montane Plant Potentilla glandulosa ssp ashlandica
©Brother Alfred Brousseau, St. Mary's College

29. Experimental Outcome: Growth of Potentilla Clones

30. What is the relationship between these organisms?
Interpretation Part I
Not a pure plastic response
Not a pure genetic response
What is the relationship between these organisms?
Separate experiments show that crosses between different source populations produce viable offspring

31. Interpretation Part II
These are not different species
What then are they?

32. Ecotypes the middle ground
Genetically distinct organisms
Phenotypically distinct in terms of
Morphology
Physiology
Phenology
Occur in distinct habitats
Differences can be traced to ecological differences in home habitat
Plants are potentially interfertile (i.e., same biologicial species)

33. An Interpretation
Individuals or Ecotypes

34. Selection Within a Population

35. Purple loosestrife (Lythrum salicaria): an aggressive invasive species

36. Purple Loosestrife and Tristyly
Three flower types (morphs)
♀  Pistal positions differ
♂ Stigma positions differ
Pollination patterns
No self pollination
Each morph can pollinate the other two morphs
Less frequent morphs have higher fitness

37. Impact of Frequency-Dependent Selection on
Invading Populations of Purple Loosestrife
Study system with 24 newly invaded
sites censused over a 5 year period
Low evenness during year zero
Evenness predicted to increase due to frequency dependent selection among morphs
No change line
(y=x)
Prediction is met, indicating a change in population due to natural selection

38. Selection At a Global Scale

39. Convergent Evolution Example #1: Desert plants
Euphorbiaceae: Africa
Cactaceae: N. America
Example #2: Alpine plants
Campanulaceae: Africa
Asteraceae: S. America

40. Life Histories and Tradeoffs

41. Key Stages in the Life-History of a Plant
Seed Maturation
Growth
Dispersal
Flowering
seed phase
Dormancy
Pollination
Germination

42. The Ideal Plant Grow large rapidly Live forever
Reproduce early and often

43. Impact of
Limiting Resources

44. General Scheme of Resource Allocation
Reproduction
Pollen
Nectar
Ovules
Seeds
Growth
Leaves
Stems
Roots
Rhizomes
Maintenance
Structural support
Storage
Defenses
Basal metabolism 3 2 1
General order in which resources are used