mechanisms of evolution. review 1) have living things become more or less complex over time? 2) the...
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MECHANISMS OF EVOLUTION
Review
1) 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.
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
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.
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
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)
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
When a severe event results in a drastic reduction in numbers.
Very small sample of alleles survives to establish a new population.
Founder Effect
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
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
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 increaseSuccess of hummingbirds increase success of flowers etc.
Directional Selection
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
Salmon: large population and short generation time. Many offspring produced. Amount of genetic variation from both recombination and
mutation increased. Gill-net fishing in Upper Johnston Strait from 1950-1974 Average weight of salmon decreased by about 1/3. Smaller salmon more likely to escape and contribute to
next generation.
Disruptive Selection
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 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)
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?
In some species, females choose mates based on physical traits: Bright colouration Behavioural traits (courtship displays) 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. Attract, and sometimes forcibly detain, the females.
Compromise between different selective pressures Traits beneficial for mating but otherwise
detrimental Runaway Selection:
feature has become extremely exaggerated due to preferential mating.
Penguin Puzzlement
Non-animal Sexual Diversity
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
Read the Case Study article provided and answer the questions.
The Evolution of Complex Features 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 Sudden production by chance of a fully functional eye?
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 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?
Organism would be strongly favoured.
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, can avoid light.
This population more successful.
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
Mutualism: relationship between 2 organisms in which both organisms benefit.
alfalfa plant and nitrogen-fixing bacteria Flowering plants (250,000 species) and
bees.
Gymnosperms: ex// grass (non-flowering). Produce large quantities of pollen chances of of wind-borne
pollen reaching egg is slim. Non-sticky pollen.
Angiosperms: flowering plants. 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
When a new species is formed Species: individuals which can
interbreed.
Modes of Speciation
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.
Sympatric Speciation: split into separate gene pools and continue to share a similar geographic location. One mode is reproductive isolation.
Mimicry: An Evolutionary Phenomenon!
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
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)
“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.
Ex// several palatable butterflies mimic different species from the highly noxious species in genus Battus.
Ex// the false cobra is a mildly venomous but harmless snake which mimics the characteristic ‘hood’ of an indian cobra’s threat display.
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.
Youtube video!
http://www.youtube.com/watch?v=H8oQBYw6xxc
Mullerian Mimicry
Two or more species have very similar warning or aposematic signals and both share genuine anti-predation 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?)
Ex// unpalatable Euploea species look very similar.
Both are poisonous.
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.
Ex// aposematic feature: warning colouration. Advertising signal Usually bright, striking colouration.
Mertensian Mimicry
Rare Unusual case where deadly prey mimic a
less dangerous species.
(How would this be beneficial to the mimic?)
Seatwork/Homework
Review this lecture. Organize the topics in your own notes.