1. Chapter 22
The Origin of Species

2. What You Need to Know: The biological concept of a species.
Speciation may occur when two populations become reproductively isolated from each other.
There are prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations.
How allopatric and sympatric speciation are similar and different.
How a change in chromosome number can lead to sympatric speciation.
Why speciation rates are often rapid in situations where adaptive radiation occurs or during times of ecological stress.
The connection between speciation in a isolated population and a change in gene frequency, a change in the environment, natural selection, and/or genetic drift.
How punctuated equilibrium and gradualism describe two different tempos of speciation.

3. Speciation = origin of species
Microevolution: changes in allele frequencies within a single gene pool
Macroevolution: evolutionary change above the species level
cumulative effects of speciation over long periods of time

4. HHMI Video Clip: Reproductive Isolation and Speciation
Running Time: 2:38 min

5. Biological Species Concept
Species = population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
Reproductively compatible
Reproductive isolation = barriers that prevent members of 2 species from producing viable, fertile hybrids

6. Types of Reproductive Barriers
Prezygotic Barriers:
Prevent mating or hinder fertilization
Types:
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Postzygotic Barriers:
Prevent hybrid zygote from developing into fertile adult
Types:
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown

7. Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN

8. Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN

9. Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN

10. Types of Reproductive Barriers
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN

11. Other definitions of species:
Morphological – by body shape, size, and other structural features
Ecological – niche/role in community
Phylogenetic – share a common ancestor, form one branch on tree of life

12. Two main modes of speciation

13. Two main modes of speciation:
Allopatric Speciation
“other” “homeland”
Geographically isolated populations
Caused by geologic events or processes
Evolves by natural selection & genetic drift
Eg. Squirrels on N/S rims of Grand Canyon
Sympatric Speciation
“together” “homeland”
Overlapping populations within same geographic area
Gene flow between subpopulations blocked by:
polyploidy
habitat differentiation
sexual selection
Eg. polyploidy in 80% of plants (oats, cotton, potatoes, wheat)

14. Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon

15. Sympatric Speciation by Polyploidy
Autopolyploid: extra sets of chromosomes
Failure of cell division (2n  4n)
Eg. Strawberries are 4n, 6n, 8n, 10n (decaploid)!

16. Allopolyploid: 2 species produce a hybrid
Species A (2n=6) + Species B (2n=4)  Hybrid (2n=10)

17. Hybrid Zone
Occurs when species with incomplete reproductive barriers come into contact with one another

18. Hybrid Zones
Possible outcomes: reinforcement, fusion, stability

20. Fusion: The breakdown of reproductive barriers

21. Grizzly
Polar
“Grolar” or “Pizzly”

22. Time Course of Speciation
Gradualism
Common ancestor
Slow, constant change
Punctuated Equilibium
Eldridge & Gould
Long periods of stasis punctuated by sudden change seen in fossil record

24. HHMI Short Film: Lizards in an Evolutionary Tree
Topic: Adaptive Radiation
Running Time: 17:50 min