natural selection • variation within speciesguralnl/gural/454outcomes of evolution.pdf · natural...
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Outcomes of evolution
• Natural Selection• Variation within
species
Quaking Aspen: genet and ramets,10,000 yrs old
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Variation and natural Selection
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Natural Selection
• Requires variation• Heritability• Environmental
change• Adaptive traits• Differential
reproduction
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Heritability: Brassica campestris
• Resemblance among relatives due to shared genes
• If offspring matched parents exactly then the correlation would be 1.0
• No relationship would be 0.0
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Heritability
• VP= phenotypic variance
• VG= genetic variance • VE= environmental
variance • VP= VG + VE
• H2= VG/VP
• Total genetic contribution to phenotypic variability
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Narrow-sense Heritability• Potential response
to selection• Additive variance=
each allele adds equally to the phenotype
• Dominance variance = A is dominant to a so AA and Aa have the same phenotype
• VG= VA + VD
• h2 = VA/ VE + VA + VD
• High h2 prediction of impact of selection in altering a population.
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Adaptation
• Any heritable behavioral, morphological or physiological trait
• that maintains or increases the fitness
• of an organism• under a given set of environmental
conditions.
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Plasticity
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Relative Fitness
• The contribution an organism makes to future generations and the population gene pool.
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Types of selection
Directional Stabilizing
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Three Patterns
• Specialists: perform best in different environments
• Phenotypically plastic: match the most fit trait value for each set of environmental conditions
• Generalists: converge on a single phenotype intermediate and can survive in all environments
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Variation
• Mutation: ultimate source of genetic variation
• Migration: seed and pollen dispersal
• Increase variation
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Variation: Genetic drift
Population size important
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Migration works to keep nearby clusters the same: pink next to pink whileDistant populations can easily be different.
Small populations will lose variation due to drift
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Variation within species
• Clines• Ecotypes • Acclimation
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Clines• Heavy Metal
tolerance• Gradient over short or
long distance• Trade-off grow well in
contaminated soil, poor growth in normal soil
• Reduce cross pollination
Mine tailing individuals flower earlierPlants near boundary self pollinate
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Ecotypes
• Ecotypes: populations of a species from different habitats/locations that possess genetically based differences in appearance or function
Height variation
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Achillea lanulosa
• three gardens • 4 ecotypes • Results in common
gardens • Mather population
(1400 m) grown in different gardens
• Inherited variation
Timberline, Mather & Stanford
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Differences• Morphology (growth
form, leaves)• Phenology (timing of
flowering, dormancy)• Mather: thinner
boundary layer, close to air temperature
• Timberline: compact, thicker boundary layer, warmer
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Ecophysiological variation
• Sorrel (Oxyria digyna)• Alpine and arctic • Enzyme data • Acclimation
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Photosynthetic response
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Enzyme data
• Enzyme response to incubation at 50oC• Environmental preconditions
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Summary
• Heritable variation• Selection• Trade-offs• Co-evolution species interactions