part of as 90717 relates to us 6317. what is evolution ? evolution is change over time - change...
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Part of AS 90717
Relates to US 6317
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What is EVOLUTION ?
Evolution is change over time -
Change means heritable change in a population
Time means over generations
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Example: Evolution of polar bears
Polar bears feed only on the Arctic Ocean ice, available since less than 5 million years ago.
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Seals swim under the Arctic ice, but have to keep breathing holes open.
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Q: So where did polar bears come from?
A: they share a common ancestor with brown bears.
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TIME
EvolutionarychangeSpecies A
Brown bear
Species B
Polar bear
1. Mutation (white fur)2. Hunting advantage (seals can’t see white bears so well)3. Better breeding success (more white cubs)4. Increased % white bears in population over time5. Reproductive isolation (polar/brown bear hybrids infertile)
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anagenesis = change within a population;
cladogenesis = branching to produce 2 new species.
Two patterns of speciation:
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Biological species concept: a species is “a population or group of populations whose members have the potential to interbreed with one another to produce viable fertile offspring, but which cannot produce viable fertile offspring with members of another species.”
i.e. this species concept is based on interfertility rather than physical similarity.
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By this definition, separate species must be reproductively isolated.
Geographical isolation by itself ≠ reproductive isolation – it is not a feature of the organisms themselves.
http://www.creativegraphics.ws/main/Information/funbets/Gallery/ExtraPhotos.html www.geocities.com/ zedonknzorse/
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Habitat isolation
Behavioural isolation
Temporal isolation
Pre-zygotic isolating mechanisms operate before fertilisation:
Mechanical isolation
Gametic isolation
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Post-zygotic isolating mechanisms operate after fertilisation:
Hybrid breakdown
Reduced hybrid viability Reduced hybrid fertility
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Two modes of speciation
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Has speciation occurred during geographic isolation?
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Species A
TIME
Species B
Species C
Sequential Evolution
Species A is replaced by B, then by C
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Appearance of sequential evolution in the ancestry of horses(only one species survives).
1990s
Extinct horses Modern horses
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Species A
TIME
Species B Species C
Divergent Evolution
Species A is replaced by two or more coexisting species.
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Ancestral parrotfrom Australia
TIMEDivergent Evolution
80 mya
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Ancestral parrotfrom Australia
TIMEDivergent Evolution
Kaka
tree
80 mya
60 mya
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Ancestral parrotfrom Australia
TIMEDivergent Evolution
Kaka Kakapo
groundtree
80 mya
60 mya
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Ancestral parrotfrom Australia
TIMEDivergent Evolution
Kaka Kakapo
groundtree
80 mya
60 mya
3 mya
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Ancestral parrotfrom Australia
TIMEDivergent Evolution
Kaka Kakapo
groundtree
Kea
alpine
80 mya
60 mya
3 mya
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Ancestral parrotfrom Australia
TIME
Kaka-North Island
Kaka –South Island
Divergent Evolution
Kaka Kakapo
groundtree
Kea
alpine
80 mya
0.4 mya
60 mya
3 mya
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Fleming 1979
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Species A
TIMERadiation
Species C Species DSpecies ESpecies B
Many descendant species in different places
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Adaptiveradiationof NZwrens
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Two models for the tempo of speciation
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From: Arensburger et al. (2004), J. Biogeogr. 31: 1769-1783
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Species A
TIMEConvergent Evolution
Species X
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Species A
TIME
Species B
Convergent Evolution
Species X
Species ZSpecies C Species Y
Unrelated species look similar if they live in similar environments
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Sabre-tooth tigers
Marsupial Placental
Simpson 1980:70
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Convergence in unrelated, streamlined swimmers
Shark - fish Dolphins - mammals
Common features: both adapted to move in water Dorsal, pectoral fins, hydrodynamic shape
Differences: tail flukes reflect different ancestrySharks always aquatic, dolphins descended from land animals
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Why does evolution keep going?
Why do we not get perfection??
Because:The world is always changing, producing new challenges and opportunities.
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Continental drift
Fig 15.3A
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