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

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

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

Genotype by Environment Interactions Response by a single genotype

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

Genotype by Environment Interactions VE

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

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

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

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

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

Evidence of Selection in Natural Plant Populations

Selection Among Populations

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

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

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

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

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

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

Stanford Common Garden

Mather Common Garden

Timberline Common Garden

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

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

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

Potentilla glandulosa A Second Example Potentilla glandulosa Copyright © 1997-2001 by Jane Strong and Tom Chester http://tchester.org/sgm/conditions/blooms/idyellow.html

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

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

Experimental Outcome: Growth of Potentilla Clones

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

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

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)

An Interpretation Individuals or Ecotypes

Selection Within a Population

Purple loosestrife (Lythrum salicaria): an aggressive invasive species

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

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

Selection At a Global Scale

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

Life Histories and Tradeoffs

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

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

Impact of Limiting Resources

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