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Darwin

• 1835 _____________visited the Galapagos Islands and became convinced various populations evolved from ancestral form.

• 1838 After reading an essay by __________________, he theorized some individuals would have a competitive advantage conferred by favorable characteristics.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Darwin’s Theory of Natural Selection

• • – Some are heritable.

•

•

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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• Augustinian Monk– Studied garden pea (Pisum sativum).– Discovered characteristics pass from parent to

offspring in form of discrete packets called genes.• Exist in alternate forms - alleles.• Some prevent expression of others.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Big Picture…

• Phenotypic variation among individuals in a population results from the combined effects of …

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Big Picture…

• The Hardy-Weinberg equilibrium model helps identify …

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Big Picture…

• ________________ is differential survival and reproduction among phenotypes.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Big Picture…

• The extent to which phenotypic variation is due to genetic variation determines ….

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Big Picture…

• Random processes, such as genetic drift, can…

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Variation Within Populations

• Variation in Plant Populations– Many plant species differ dramatically in form

from one elevation to another.• Clausen et al. found evidence of adaptation by

ecotypes to local environmental conditions in Potentilla glandulosa.–

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Variation Within Populations

• Variation in Plant Populations– Phenotypic differences (growth and flower

production) within clones grown at the 3 elevations are the result of environmental differences•

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Variation in Animal Populations

• Genetic Variation in Alpine Fish– Movement of cold adapted aquatic species into

the headwaters of glacial valleys that lace the Alps created clusters of geographically isolated populations.• Douglas and Brunner used microsatellite DNA to

conclude Coregonus populations are …

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Hardy Weinberg

• Hardy Weinberg principle states that in a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Calculating Gene Frequencies

• SS (81%) SA (18%) AA (1%)– Frequency of S allele ?• =

–

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Conditions Necessary for Hardy Weinberg

• • • • • …Between All Genotypes– Likely, at least one of these will not be met and

allele frequencies will change.• Potential for evolutionary change in natural populations

is very great.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Natural Selection

• Some individuals in a population, because of their phenotypic characteristics, will have higher survival and produce more offspring.– ________________ is the measure of an

individual’s contribution of offspring, or genes, to future generations.

– Natural selection can…

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Stabilizing Selection• __________________ acts to impede changes

in a population by acting against extreme phenotypes and favoring average phenotypes.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Directional Selection• ____________________ leads to changes in

phenotypes by favoring an extreme phenotype over other phenotypes in the population.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Disruptive Selection• ________________ creates bimodal distributions

by favoring two or more extreme phenotypes over the average phenotype in a population.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Evolution by Natural Selection

• Natural selection, which changes genotypic and phenotypic frequencies in populations, can result in adaptation to the environment.– Depends on ________________ of trait.

h2 = VG / VP

• VG : Genetic variance

• VP: Phenotypic variance

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Adaptive Change in Colonizing Lizards

• Losos et al.– Genus Anolis• Great diversity includes large amount of variation in

size and body proportions.– Length of hind limbs appears to reflect …

» Diameter of perching surfaces.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Rapid Adaptation by Soapberry Bugs

• Carroll and Boyd– Soapberry Bug (Jadera haematoloma) feeds on

seeds from family Sapindaceae.• Slender beaks to pierce fruit walls.

– Distance from outside fruit wall to seeds varies widely - …

» Found close relationship between …

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Change Due To Chance

• Working in teams complete the simulation on Population Genetics…

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Change Due To Chance

• Random processes such as _____________ can change gene frequencies in populations, especially in small populations.

• Major concern of ____________________ is reducing habitat availability to the point where genetic drift will reduce genetic diversity within natural populations.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Evidence of Genetic Drift in Chihuahua Spruce

• Picea chihuahuana now restricted to peaks of Sierra Madre Occidental in N. Mexico.– Ledig et al. examined populations to determine if

the species has lost genetic diversity as a consequence of reduced population size.• Found significant …

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Genetic Variation In Island Populations

• In general, genetic variation is _________ in isolated and generally smaller, island populations.– Reduced genetic variation indicates a lower

potential for a population to evolve.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Genetic Diversity and Butterfly Extinctions

• Frankham and Ralls point out ___________ may be a contributor to higher extinction rates in small populations.– Reduced fecundity, depressed juvenile survival,

shortened life-span.

• Saccheri et al. conducted genetic studies on populations of Glanville fritillary butterflies (Melitacea cinxia).– Populations with highest levels of inbreeding had…

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Evolution and Agriculture

• “_____________________” is used to describe selective breeding of domesticated organisms to produce or maintain desirable traits.

• “_____________________” is the introduction or deletion of genes in domesticated organisms.– These organisms are termed “genetically modified

organisms” or GMOs.

BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection

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Unintended Evolutionary Consequences

• The use of chemicals in agriculture can have evolutionary consequences– Plant and animal pests may evolve resistance to

the chemicals used to control them• Resistance among pests have been shown to be quick

and widespread– Vila-Aiub et al. showed how Johnsongrass quickly evolved

resistance to herbicides in Argentina

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BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection