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3/5/19
1
Speciation
• What is a species? • Reproductive isolating mechanisms
– Pre-mating – Post-mating
• How do species arise? – Allopatric speciation is most common – Sympatric speciation can happen
occasionally – Polyploid speciation (mostly plants)
March 6,2019
What is a species?
Eastern Meadowlark Western Meadowlark
Reproductive Isolating Mechanisms
Prezygotic barriers Habitat
Isolation Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Individuals of
different species
MATING ATTEMPT FERTILIZATION
(a) (c) (e) (f)
(b)
(g)
(d)
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
FERTILIZATION VIABLE, FERTILE
OFFSPRING
Postzygotic barriers
(k)
(h) (i)
(j)
(l)
Pre- or post- zygotic? What kind of reproductive isolation?
Temporal Isolation: timing of reproduction differs
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Behavioral Isolation Mechanical isolation
http://homepages.indiana.edu/web/page/normal/20691.html
pygidium
paramere
Mechanical Isolation
Damselfly genitalia
Allopatric Speciation
Allopatric Speciation A. formosus
Atlantic Ocean
A. nuttingi
Isthmus of Panama
Pacific Ocean
A. panamensis A. millsae
Frog speciation in response to habitat isolation Kok et al 2017 J. Biogeography
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Hawaiian Honeycreepers and Island age
https://www.theguardian.com/science/punctuated-equilibrium/2011/nov/02/hawaiian-honeycreepers-tangled-evolutionary-tree
Allopatric Speciation on Islands Laboratory experiments can produce (partial) reproductive isolation after a few generations
EXPERIMENT
RESULTS
Initial population of fruit flies
Some flies raised on starch medium
Mating experiments after 40 generations
Some flies raised on maltose medium
Female
Starch Maltose
Mal
e M
alto
se
Star
ch
Number of matings in experimental group
22 9
8 20
Female Starch
population 1
Mal
e St
arch
po
pula
tion
2
Number of matings in control group
18 15
12 15
Starch population 2
Star
ch
popu
latio
n 1
Preference for mating with the same type of fly
Sympatric Speciation Speciation without a geographic barrier
Video: https://www.youtube.com/watch?v=AqZQriiDIKM
Lake Malawi cichlids
Sympatric Speciation
Video: https://www.youtube.com/watch?v=AqZQriiDIKM
Lake Malawi cichlids
Sympatric Speciation
Some flies shifted to apples after they were introduced to North America. Speciation in progress?
Polyploid speciation can happen in plants
2N=12 2N=12
4N=24
Tragopogon miscellus
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Diploid cell from species A 2n = 6
Diploid cell from species B 2n = 4
Gamete n = 3
Gamete n = 2
Hybrid Sterile because chromosmoes can’t pair correctly in meiosis
Cell division error doubles the chromosome number.
Hybrid is now fertile
Polyploid speciation can happen in plants
Cabbage, broccoli, kale
Turnip, Chinese cabbage
Black mustard