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Speciation and macroevolution Chapter
Objectives:
- Review meiosis
-Species
-Repro. Isolating mechanisms
- Speciation
-Is evolution always slow
-Extinction
Review
Meiosis: division of cells that results
in daughter cells with one-half of
the genetic information that the
original cell had.
4
4
8
4
Diploid 2n
Pa
Haploid
n
4
Haploid n
Ma
Haploid
n
Species (Biological Species Concept)
A group of organisms with similar structural
and functional characteristics that in nature
breed only with each other and have a close
common ancestry
- a common gene pool (isolated from others)
- restricted by reproductive barriers
Junior = Zygote =
diploid organism=
2n
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Species and reproductive isolation
Problems with concept:
1. What about asexual organisms?
2. What about when two species interbreed
and produce an offspring?
• lion + tiger = “liger” (sterile)
• female horse + male donkey = mule
Reproductive isolating mechanisms
- genetic integrity is maintained
Prezygotic barriers interfere with mating!
They are prezygotic!!
1. Temporal isolation
2. Behavioral (sexual) isolation
3. Mechanical isolation
4. Habitat isolation & Geographic isolation
1.
Temporal Isolation
2. Behavioral Isolation
3. Mechanical Isolation
4. Habitat isolation & Geographic isolation
•Closey related species that occur in different
habitats
•Geographically separated
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Species and reproductive isolation
Hybrid Sterility
Postzygotic barriers prevent successful reproduction
when mating does occur:
1. Hybrid inviability: (embryonic hybrid dies)
2. Hybrid sterility: (hybrid is sterile - no gametes)
Female
horse
Mule
(Sterile)
Male
donkey
3. Hybrid breakdown = F2 Hybrid has defect: F1hybrid
Okay but offspring doesn’t reproduce well
4 Gamete Isolation: gamete doesn’t fertilize egg at all
The key to speciation is reproductive isolation.
Speciation:
The evolution of a new species.
1. Allopatric speciation
(Allo = different) patri = fatherland
2. Sympatric speciation
(Sym = “together”)
Sypatric Speciation:
- Long physical
isolation
- Different selective
• Allopolyploidy: (Plants) Multiple sets of
chromosomes from > 2 spp.
pressures
• Changing ecology (fruit maggot flies in
Hudson River valley)
Kaibab squirrel??
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Polyploidy
Hybrid
Species A
2n = 6
Species B
2n = 4
P generation
n= 3
n= 2
Gametes
They eat, mate,
and lay eggs on
different hosts
Hybrid AB
F1 generation
No doubling of
chromosome number
Doubling of
chromosome number
2n = 10
Chromosomes either
cannot pair or go
through erratic meiosis
Pairing now
possible
during meiosis
n= 5
Hawthorne maggot fly range (parasitic on native hawthorne)
No gametes or sterile
gametes-no sexual
reproduction possible
Viable gametes-sexual
reproduction possible
(self-fertilization)
Apple maggot fly and Hawthorn maggot fly range
(parasitic on domestic apples)
Slide 3
Hybrid Zones
Is evolutionary change fast or slow?
• Areas of overlap where interbreeding
might occur?
•
– i.e., Reproductive barrriers break down
Slide 5
Darwin’s view predicts slow gradual
change?
• Does the fossil record support this?
- Mule deer & white-tailed deer
- Red-shafted flicker & yellow shafted
flicker
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Macroevolution: Large scale phenotypic changes
- radical changes that create new species
Driving forces behind macroevolutionary changes?
1. Evolutionary novelties?
2. Adaptive radiation?
2. Mass extinction?
1. Evolutionary novelties
Recall: Evolution works on existing things (its
conservative)
Pre-adaptations: variations on a pre-existing structure
- originally filled one role – changed in a way to
become adaptive for a different role
- feathers? Scales (protection/insulation) to
insulation/flight
How might such a novelty occur?
- mutation in a gene?
- e.g. Developmental gene – that regulates
development of an organism
Consider Allometric growth
- different parts of body grow at different rates
- slight change in gene (mutation) cause different
growth rates of different body parts
fiddler crab – sun fish – t-rex?
How would such a novelty occur?
- mutation in a gene?
- e.g. Developmental gene – that regulates
development of an organism
Mutation of a developmental gene
- Axolotl salamander:
mutation prevented maturation
• Remember evolution is conservative
Paedomorphosis
Fig. 20-14b, p. 440
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2. Adaptive radiation
•
The evolution of many related species
from an ancestral species
a
b
c
d e
z
- adaptive zones (ecological niches)
3. Extinction!!!!!!!!!!!!!
Is the process of extinction evolution?
Background vs. Mass extinction
6th Great Extinction!
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