Download Mechanics of evolution

MECHANISMS OF
EVOLUTION
Review
Have living things become more or less complex over time?
2)
The most common fossils/impressions are found in ____________ rocks. What are these?
3)
Earth is __________ years old.
4)
Explain the Origin of Life in four steps.
5)
Define the following: amino acid, polypeptide, nucleotide, microsphere, fatty acid,
heterotroph, autotroph.
6)
What is the heterotroph hypothesis?
7)
What did the Stanly Miller experiment infer?
8)
Define abiogenesis.
9)
How did autotrophs come to exist?
10)
What is the main reason why the fossil record doesn’t extend past 530 million years?
11)
Differentiate between Lamarck and Darwin in terms of their theories of Evolution. How were
they similar?
12) Define ‘natural selection’
13) Define ‘survival of the fittest’
14) Summarize natural selection in 6 points.
1)
Review (2)
15) What is a homologous structure? Give an example of this.
16) What is a vestigial organ? Give an example.
17) How is embryology evidence of evolution?
18) How are biochemistry and genetics evidence of evolution?
19) Outline how Peppered Moths are good examples of evolution.
20) True or False? Evolution happens quickly. Explain your response.
21) True or False? Mutation occur because of the changes in the environment.
22) What is a species? What is speciation?
23) How can geographic isolation lead to speciation?
24) How can reproductive isolation lead to speciation?
25) What is adaptive Radiation? Example?
26) Define convergent evolution.
27) Traits arising through convergent evolution are termed ________________ , whereas traits
which have a common origin are called ______________________________.
28) What is ‘stabilizing selection’?
Random Change
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Key factors of evolution
 When
a population is small, chance fluctuations can
cause changes in allele frequencies (Why?)
 When mating opportunities are nonrandom, individuals
that are preferred as mates will pass on their alleles in
greater numbers than less preferred mates (Why?)
 When genetic mutations occur, new alleles may be
created or one allele may be changed into another,
thereby changing the frequencies of both new and
original alleles.
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When individuals migrate, thy remove alleles from
one population and add them to another.
When natural selection occurs, individuals with
certain alleles have greater reproductive success
than others do, thereby increasing the relative
frequency of their alleles in the next generation.
REAL POPULATIONS ARE AFFECTED BY ANY OF THE
FORMER SITUATIONS, RESULTING IN CHANGES TO
ALLELE FREQUENCIES.
Genetic Drift
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Small pop – chance plays a significant role in
altering allele frequencies.
Genetic drift: change in the genetic makeup of a
population resulting from chance.
(DEMO)
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In small population, allele frequency fluctuates wildly from
generation to generation.
In larger populations, allele frequency remains relatively
stable.
Think: genetic drift demo.
Bottleneck Effect
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When a severe event
results in a drastic
reduction in numbers.
Very small sample of
alleles survives to
establish a new
population.
Founder Effect
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Genetic drift that results when a small number of
individuals separate from their original population
and create a new population.
Ex// a few seeds carried by a bird or wind to distant volcanic
island.
 Common in self-pollinating plants: entire populations from
one seed!

Example of Founder Effect:
 Members
of Amish community in Pennsylvania are all
descendants of about 30 people who emigrated from
Switzerland in 1720.
 One of the founders had a rare recessive allele that
causes unusually short limbs.
 Frequency of allele in community is about 7%, whereas
frequency in most populations is 0.1%.

Example of Founder Effect:
 Juvenile
large ground finches, Daphne Major, visited
the Galopagos Islands every year.
 One year, 2 females and 3 males remained to breed.
 Produced 17 young  founders of new population.
 Inheritable traits were measured: founding population
had a different genetic composition from that of the
original large population.
Alleles by chance...
Gene Flow
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The movement of alleles from one population to another
through the movement of individuals or gametes.
When organisms migrate, alter the allele frequencies of
original population as well as the new population.
Genetic info shared between 2 populations.
Reduces differences between populations.
Ex// Prairie Dogs
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Live in dense colonies of a few dozen members.
Prevent other prairie dogs from joining colony.
However, in late summer, allow mature male pups from other
colonies to enter.
Affects both gene pools.
Patterns of Selection

Stabilizing Selection
 Most
species show little change over periods lasting
thousands of years.
 Occurs when the most common phenotypes within a
population are most favoured by the environment.
 Most common form of selection.
 Ex//
Hummingbird: draws nectar from flowers with a long
bill and tongue. Bill and tongue length are well adapted for
the size of flowers they feed on in their local environment.
Why wouldn’t ALL hummingbirds have long bills/tongues?
Longer bill requires more nutrients and energy to grow and carry around.
Shorter bill reduces a bird’s ability to reach food.
Ideal bill length also increases pollination  increase flower population  increase
Success of hummingbirds  increase success of flowers  etc.
Directional Selection
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Occurs when environment favours individuals with
more extreme variations of a trait.
Ex// if hummingbird migrates to area with longer
flowers, longer-billed hummingbird favoured.
Directional Selection and Human
Activity
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Salmon: large population and short generation time. Many offspring
produced.

Amount of genetic variation from both recombination and mutation increased.
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Gill-net fishing in Upper Johnston Strait from 1950-1974
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Average weight of salmon decreased by about 1/3.
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Smaller salmon more likely to escape and contribute to next generation.
Disruptive Selection
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Favours individuals with variations at opposite extremes of a trait.
Ex// 2 flowers with different-sized flowers available as food source for
one hummingbird population.
Neither is well suited to a hummingbird with average bill length.
Distinctive groups may eventually become isolated breeding populations
with separate gene pools  speciation?
Example of Disruptive Selection
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Black-bellied seedcracker finch.
Depend on seeds of two different types of sedge
 soft and hard.
Small bills for soft seeds, larger bills for hard seeds.
Sexual Selection
Favours the selection of any train that influences the
mating success of the individual.
 Sexual dimorphism: striking differences in physical
appearance of males and females.
 Behavioural Differences between sexes.
 Most common forms of sexual selection result from
female mate choice and from male-versus-male
competition.
(http://www.youtube.com/watch?v=D92AUXhYZ0M)
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Evolution of Sexual Selection?
http://www.youtube.com/watch?v=VihkIrkLoC0
This video is from 1932. The narrator describes the mould as a
plant. How is this wrong?!
In the enchanting 'The Mystery of Marriage' comparisons
are drawn between the courtship and marriage rituals of
animals and plants with that of humans.
Are there similarities between other organisms and humans?
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In some species, females choose mates based on physical traits:
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Bright colouration
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Behavioural traits (courtship displays)
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Size of physical features
In other species, males equipped with physical features that assist them in
establishing control of and defending their territory against other males.
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Attract, and sometimes forcibly detain, the females.
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Compromise between different selective pressures
 Traits
beneficial for mating but otherwise detrimental
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Runaway Selection: feature
has become extremely
exaggerated due to
preferential mating.
Penguin Puzzlement
Non-animal Sexual Diversity
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Most plants do not select mates
 Need
to attract various agents – insects, birds, bats – to
assist in pollination.
 Flowers and scents.
Bright colours of plants help pollinators find them.
The Evolution of Antibiotic Resistance in
Bacteria
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Read the Case Study article provided and answer
the questions.
The Evolution of Complex Features
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Consider how an organism with a complex eye could
have evolved from an ancestor with no eyes at all.
How might mutation and selective pressures have
initiated the evolution of an eye?
Two scenarios
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Sudden production by chance of a fully functional eye?
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Many thousands of beneficial mutations to occur at once.
Likelihood is remote.
Gradual production due to series of accumulated beneficial
mutations. Each stage must have benefited the organism.
Theory of the Evolution of the Eye
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Worm-like ancestor experienced mutation that
resulted in the development of light-sensitive skin
cells.
Light would have triggered chemical change  for
example, stopped moving in the light.
 Reduce
organisms change of attracting attention of
predators?
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Organism would be strongly favoured.
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After a million or so years, another mutation occurs
 Pitted
skin surface
 Having light-sensitive cells in a pit could have provided
major benefit allowing worm to distinguish the direction
of a light source.
 Therefore,
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can avoid light.
This population more successful.
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Any mutation causing pit to be exaggerated would
enhance directional sensitivity.
A mutation resulting in the narrowing of the
entrance to the pit could have been beneficial
resulting in an eye capable of forming a crude
image.
Crude lens may have been formed from transparent
productive coating.
Evolution of Mutualism
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Mutualism: relationship between 2 organisms in
which both organisms benefit.
alfalfa plant and nitrogen-fixing bacteria
Flowering plants (250,000 species) and bees.
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Gymnosperms: ex// grass (non-flowering).
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Produce large quantities of pollen  chances of of wind-borne pollen
reaching egg is slim.
Non-sticky pollen.
Angiosperms: flowering plants.
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Most likely evolved from gymnosperms.
Mutation caused pollen to become slightly sticky  reduction in pollen
dispersed by wind.
Advantage: adhering to legs and backs of insects who eat pollen as
food  next plant possibly pollinated.
Followed by evolution of attractive features: colourful leaves or petals,
fragrance, and nectar.
Specialized: orchid blossom resembles body of a queen bee to attract
male agent of pollination.
Speciation
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When a new species is formed
Species: individuals which can interbreed.
Modes of Speciation
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Allopatric Speciation: also known as geographical
isolation.
 When
two populations become geographically
separated from one another.
 Large
river or canyon
 Mountain ranges
 Human activity: dams, canals, or major highways.
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Sympatric Speciation: split into separate gene pools
and continue to share a similar geographic location.
 One
mode is reproductive isolation.
Mimicry: An Evolutionary Phenomenon!
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In my opinion, one of the neatest products of
evolution.
Mimicry: similarity of one species to another which
protects one or both.
 Appearance,
behaviour, sound, scent, and even
location.
 Occurs when a group of organisms, mimics, evolve to
share a common perceived characteristic with another
group, the models.
Defensive Mimicry
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Organisms are able to avoid an encounter that
would be harmful to them by deceiving an enemy
into treating them as something else.
Two major forms:
 Batesian
mimicry: where a harmless mimic poses as
harmful.
 Mullerian mimicry: two harmful species share similar
percieved characteristics.
Batesian Mimicry
 Several species
of hoverflies
mimic the stinging
species of wasp.
Batesian Mimicry (2)
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“a sheep in wolf’s clothing.”
Mimics less likely to be ‘found out’ when in low
proportion to their model.
 Example:
the ash borer, a moth, resembles the common
wasp but is not capable of stinging.
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Ex// several palatable butterflies mimic different
species from the highly noxious species in genus
Battus.
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Ex// the false cobra is a mildly venomous but
harmless snake which mimics the characteristic
‘hood’ of an indian cobra’s threat display.
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Ex// octopuses of the genus Thaumoctopus are able
to intentionally alter their body shape and colour so
that they resemble dangerous sea snakes or lionfish.
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Youtube video!
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http://www.youtube.com/watch?v=H8oQBYw6xxc
Mullerian Mimicry
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Two or more species have very similar warning or
aposematic signals and both share genuine antipredation attributes (ex// being unpalatable).
 Both
the mimic and model benefit from the interaction.
 The more individuals with the same feature, the more
likely predators will learn to avoid them.
(Human: Gang Signals?)
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Ex// unpalatable Euploea species look very similar.
Both are poisonous.
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Ex// many different tiger moths make ultrasonic
clicking calls to warn bats that they are
unpalatable. A bat may learn to avoid any
signalling moth.
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Ex// aposematic feature: warning colouration.
 Advertising
signal
 Usually bright, striking colouration.
Mertensian Mimicry
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Rare
Unusual case where deadly prey mimic a less
dangerous species.
(How would this be beneficial to the mimic?)
Seatwork/Homework
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Review this lecture.
Organize the topics in your own notes.