Sources of Genetic Variation Factors increasing variation Mutation Migration Factors decreasing variation Natural selection Genetic drift in small populations (<1000)

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

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

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

Stanford Common Garden

Mather Common Garden

Timberline Common Garden

Interpretation of Results: Pure Plastic Response Source PlantClonesCommon Gardens Location #1 Location #2 ? Location #1 Location #2 ?

Interpretation of Results: Pure Genetic Response Source PlantClonesCommon Gardens Location #1 Location #2 Location #1 Location #2 ? ?

Experimental Outcome: Growth of Mather Achiella Clones Plastic responseGenetic response

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

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

Montane Plant

Experimental Outcome: Growth of Potentilla Clones

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 ♀  Pistal positions differ Three flower types (morphs) ♂  Anther 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 Prediction is met, indicating a change in population due to natural selection No change line (y=x)

Selection At a Global Scale

Convergent Evolution Example #1: Desert plants Euphorbiaceae: AfricaCactaceae: N. America Example #2: Alpine plants Campanulaceae: AfricaAsteraceae: S. America

Life Histories and Tradeoffs

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

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

Life Histories and Tradeoffs

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 General order in which resources are used 123

General Scheme of Resource Allocation through time Time Available resource

Resource Allocation for a Typical Annual Plant Time

Resource Allocation over a typical year for a Stress Tolerating Plant Time

Tradeoffs and Limiting Resources vs