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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