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Speciation
Darwin’s finches
What is a species?
The _________-species concept:
Members of a given species produce _____ offspring
Members of different species can not
Limitations of the concept:
- Can’t test species that reproduce _________
- Can’t test _______
- Ignores ______ -level uniqueness
_________________ considers unique pops.
How does one species change into others?
One method: __________ speciation
‘Different ____________’
1) Population becomes divided into _______
Subpopulation 1
Subpopulation 2
Range of
original population
Dispersal = ability to _____
Dispersal
barrier
Examples of geographic isolation:
a. __________break up
E.g., Gondwanaland and the ratite birds
(135 m.y.a.)
b. ______ dig canyons
E.g., Grand Canyon
and antelope squirrels
c. Spring-fed lakes ________
E.g., Death Valley and pupfish
d. “_______” get isolated on islands
E.g., ________ finches
Birds arrive on one island
Eventually ______ to others
Habitats ____ between islands
Different islands/habitats provide different _____
2) _________ isolation
_________ gets cut off or reduced
Movement ________ areas is difficult or impossible
Most mating occurs ______ areas, not across areas
3) Differential mortality
_______ factors become different between areas
- climate
- predators
- diseases
4) Genetic Drift
__________ become different between areas
- Certain traits get selected for or against _________
- Certain alleles get eliminated from ________
- New alleles arise through ________ on one side
5) ___________ barriers develop
Final stage of __________
Prohibits successful _______ across subpopulations
E.g., behavioral reproductive barriers
Courtship of one type doesn’t appeal to other types
Courtship of Black Grouse
Courtship of Blue Grouse
________ reproductive barriers:
E.g., ____ bones of gopher species:
claspers of insects:
female
male
After reproductive barriers evolve, if populations come in
contact again, they will remain _______ species
Speciation is complete
clasper
________ radiation: many species evolve at once
E.g., when new ________ become available
Glacial retreat, volcanic islands
Various new species adapt to different ________
E.g., Darwin’s finches:
grounddwellers
treedwellers
founder
insecteaters
Second method of speciation: sympatric speciation
“Same ____________”
Produces new species rapidly
Occurs without __________ isolation
New species evolve in the same location
Based on ________ isolation, not geographic
Occurs under 2 different circumstances:
1. Ecological isolation (slower of the 2)
a. Habitats in an area become more ______
E.g., trees invade shrubland
b. Segments of population ____ to different habitats
E.g., different foods, shelter
An example of ________ selection
c. Genetic makeup of segments _______
Survival is most likely in your own habitat type
d. Reproductive barriers eventually ________
original population
genetic divergence
ecological diversification
reproductive isolation
2. Polyploidy
Wild alfalfa
(2n=16)
Cultivated alfalfa
(2n=32)
Common in ______ and cloning animals
50% of ____ plants
Meiosis 1 fails
Chromosome number doesn’t get ______
Gametes become ______
Offspring are ______ (tetraploid)
Can’t breed with _______ diploid type
Reproduce by self-_________ or cloning
Is a new, polyploid, species
Instantly!
How fast does allopatric speciation occur?
Not well understood, yet
Takes too long to observe in multicellular organisms
Species with short ________ times speciate faster
Change is usually ________
Large, sudden, changes are usually maladaptive
In fossil record, significant change takes >______yrs
Punctuated equilibrium
# of species
Periodic surges of evolutionary change
Periods of “stasis” interrupted by rapid change
extinction < speciation
stasis
extinction = speciation
stasis
extinction = speciation
extinction > speciation
extinction > speciation
Time
Occasionally, geological events wipe out ____ species
Global cooling, sea-level change, asteroid strike
_________ meteor, 6 mi diameter, 65 m.y.a.
Caused extinction of ________
_______ species then “radiated” into available ______
Then a period of stasis - gradual change - returned
The next “_____ extinction” is now underway