Post on 17-Jan-2016
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Chapter 24: The Origin of Species
1. What is a species?- A population whose members can interbreed in nature and
produce viable, fertile offspring- aka….reproductive isolation
2. What kinds of barriers keep different species isolated so they cannot mate?- Figure 24.4- Pre–zygotic barriers – before mating &/or zygote is formed- Post–zygotic barriers – after zygote is formed
Figure 24.4 Reproductive Barriers
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Individualsof differentspecies
Matingattempt
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION
(b)
(a)(c)
(d)
(e)
(f)
(g)
Viablefertile
offspring
Reducehybrid
viability
Reducehybridfertility
Hybridbreakdown
Fertilization
Gameticisolation
GAMETIC ISOLATION REDUCED HYBRID VIABILITY
REDUCED HYBRID FERTILITY HYBRID BREAKDOWN
(h) (i)
(j)
(k)
(l)
(m)
Chapter 24: The Origin of Species
1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?
- Allopatric speciation - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island
- Sympatric speciation- intrinsic factors such as chromosomal changes (plants) or
non-random mating alter gene flow
Figure 24.5 Two main modes of speciation
(a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population.
(b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation.
Chapter 24: The Origin of Species
1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?
- Allopatric speciation – - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island- Adaptive radiation
- evolution of many diversely adapted species from a common ancestor
- Seen on islands- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow
Figure 24.12 Adaptive radiation
Dubautia laxa
Dubautia waialealae
KAUA'I5.1
millionyears O'AHU
3.7millionyears
LANAI
MOLOKA'I
1.3 million years
MAUI
HAWAI'I0.4
millionyears
Argyroxiphium sandwicense
Dubautia scabraDubautia linearis
N
Chapter 24: The Origin of Species
1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?
- Allopatric speciation – - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island- Adaptive radiation
- evolution of many diversely adapted species from a common ancestor
- Seen on islands- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow
- ex. oats, cotton, tobacco, potatoes, wheat- Autopolyploidy
- An individual has more than 2 chromosome sets derived from a single species from an error in meiosis
Figure 24.8 Sympatric speciation by autopolyploidy in plants
2n = 64n = 12
2n
4n
Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.
Gametes produced by flowers on this branch will be diploid.
Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.
Chapter 24: The Origin of Species
1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?
- Allopatric speciation – - when a geographic barrier isolates a population blocks gene flow- ex. mountain range emerging, new river dividing a field, island- Adaptive radiation
- evolution of many diversely adapted species from a common ancestor
- Seen on islands- Sympatric speciation
- intrinsic factors such as chromosomal changes (plants) or non-random mating alter gene flow
- Autopolyploidy - An individual has more than 2 chromosome sets derived from
a single species from an error in meiosis- Allopolyploidy
- 2 different species produce the polyploid hybrid
Figure 24.9 One mechanism for allopolyploid speciation in plants
Meiotic error;chromosomenumber notreduced from2n to n
Unreduced gametewith 4 chromosomes
Hybrid with7 chromosomes
Unreduced gametewith 7 chromosomes Viable fertile hybrid
(allopolyploid)
Normal gameten = 3
Normal gameten = 3
Species A 2n = 4
Species B 2n = 6
2n = 10
Chapter 24: The Origin of Species
1. What is a species?2. What kinds of barriers keep different species isolated so they cannot mate?3. How are new species created?4. What is the difference between gradualism & punctuated equlibrium?
Figure 24.13 Two models for the tempo of speciation
Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations.
Time
(a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.
(b)