Adaptation and Natural Selection

1. Ecological Genetics:
Adaptation
and
Natural Selection
Prepared by: Jaycris C. Agnes

2. “Survival of the
Fittest.”

3. Ecology is the
science of
adaptation.

4. Genetic variation is
the ingredient for
Natural Selection.

5. Mutation: inheritable changes in a gene or a chromosome
Gene mutation: (point mutation)
Chromosome mutation
 deletion, duplication, inversion, translocation
Genetic Recombination
Sexual reproduction
two individuals produce haploid gametes (egg or sperm) – that
combine to form a diploid cell or zygote.
Reassortment of genes provided by two parents in the offspring
Increases dramatically the variation within a population by
creating new combinations of existing genes.
Asexual reproduction: less variation (only mutation)
Sources of Genetic Variation
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6. Nature Selection as a Force of
Evolution
 What is Darwin’s Natural Selection?
The differential success (survival and
reproduction) of individuals within the
population that results from their
interaction with their environment.
“Survival of fitness, elimination of
‘inferior’ individual”
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7.  There is variation in populations. Variation is heritable.
 In every generation some organisms are more successful
at surviving and reproducing than others. Survival and
reproduction are not random, but are related to variation
among individuals. Organisms with best characteristics
are ‘naturally selected.’
If 2 conditions are met then the population will change from
one generation to the next. Evolution will occur.
Two Conditions in
Natural Selection
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9. Evolution by Natural Selection
The major factors affecting the organisms’ survival in
the system is Fitness.
Darwinian fitness: ability of an organism to survive
and reproduce in its environment.
Adaptation is a characteristic or trait of an
organism that increases its fitness relative to
individuals that do not possess it. It is an inherited
characteristic that increases the ability of an organism
to survive and reproduce.7-20-2014 Prepared By: Jaycris C. Agnes 9

10. Peter and Rosemary Grant
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11. Geospiza fortis
Medium Ground Finch
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12. Variation in Beak Size
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13. Before and After
Natural Selection
In 1978, there was a
severe drought, small
seeds declined more than
large seeds.
Small beak birds have
difficult to find seeds, and
suffered heavy mortality,
especially females.
Conclusion:
Beak size
evolve
through
Natural
Selection.7-20-2014 Prepared By: Jaycris C. Agnes 13

14. Types of Natural
Selection

15. Directional Selection
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16. Directional Selection
Examples:
A long time ago…
Small horses died: very disadvantageous
Medium horses died: disadvantageous
Large horses prospered: advantageous
A long time ago…
Short neck giraffes died: could not reach
leaves on tree
Medium neck giraffes died: could not
reach leaves on tree
Long neck giraffes prospered: leaves
were reachable
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17. Very light-colored or
very dark-colored
oysters might be
more frequently
preyed upon by
shore birds, simply
because they are
more obvious on the
oyster bar; as a
result, the
intermediate hues
become more
common.
Stabilizing Selection
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18. Stabilizing Selection
Examples:
Short flowers die: No sunlight
Medium flowers live: Perfect conditions
Tall Flowers die: Wind damage
Lightweight babies have higher mortality rate: weaker
Average weight babies survive more often: healthy
Heavyweight babies have higher mortality rate: when being born7-20-2014 Prepared By: Jaycris C. Agnes 18

19. This might happen in
shallow water among rocks.
Light-colored oysters are
more cryptic (less easy for a
predator to see) because
they match the rock color.
Dark-colored oysters blend
into the shadows cast by the
rocks. In this case,
intermediate-colored oysters
would be most heavily
preyed upon by the crabs,
and very light and very dark
oysters would survive to
reproduce.
Disruptive Selection
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20. Disruptive Selection
Examples:
In an environment with black and white rocks…
White rabbit lives: Camouflaged
Grey rabbit dies: Seen by predator
Black rabbit lives: Camouflaged
In an environment with deep and shallow flowers…
Short beak hummingbird lives: can get pollen from flower
Medium beak hummingbird dies: cannot get pollen from flower
Long beak hummingbird lives: can get pollen from flower
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21. Five Causes of Evolution
• Mutations
• Gene flow - Emigration and immigration of
individuals (Flow of alleles)
• Genetic Drift – Changes in the gene pool of a
small population due to chance
• Nonrandom mating: (AA mates AA, Aa)
• Natural Selection
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22. Evolution is a change in
Gene Frequency
Evolution is a change of gene frequencies
within a population (or species) over time
Individuals do not evolve, populations evolve.
Focus on gene pool, collective.
But why do we see populations are still the
‘same’ over many generations?
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23. The Hardy-Weinberg Principle
The Hardy-Weinberg Principle:
Gene frequencies will remain the same in successive
generations of a sexually reproducing population if the
following five conditions hold:
– Random mating
– There is no mutation
– The population is very large
– There is no selection
– There is no migrations (isolated from other populations)
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24. The Hardy-Weinberg Principle
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25. The variation in environmental conditions
often give rise to a corresponding variation
in morphological, physiological and
behavioral characteristics.
The process in which one species gives rise
to multiple species that exploit different
features of the environment, such as food or
habitats, is called Adaptive Radiation.
Genetic Differentiation &
Adaptive Radiation
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26. Fox
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27. Bear
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28. Moth
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29. Finch
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30. Yarrow Plant
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31. END.
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