1. Origin of Species
Galapagos Tortoise

2. Origin of Species patterns of speciation
Anagenesis
A single population is transformed enough to be designated a new species
Cladogenesis
Branching evolution. A new species arises from a small population that “Buds” from a parent species.
Most species probably evolved this way. The branching evolution is the basis of biological diversity

3. Two patterns of speciation

4. Origin of Species Species definitions
Biological species = a population whose members have the potential to interbreed with one another and produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of another species. (Reproductive Isolation)
The biological species concept cannot be applied to asexually reproducing organisms
Morphospecies = species defined by their anatomical features

5. The biological species concept is based on interfertility rather than physical similarity
Eastern Meadowlark
Western Meadowlark

6. Reproductive barriers
Any factor that impedes two species from producing fertile hybrids
Prevents interbreeding between closely related species
Prezygotic barriers (impedes mating or hinders ova fertilization)
Postzygotic barriers (after fertilization)

7. Origin of Species Prezygotic barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation

8. Habitat Isolation

9. Temporal Isolation
Late-winter mating season
Summer mating season

10. Blue-footed boobies … Courtship ritual as a behavioral barrier between species.

11. Mechanical Isolation Gametic Isolation
“You can’t fit a square peg in a round hole”
Gametic Isolation
“gamete recognition”

12. Origin of Species Postzygotic barriers
Reduced hybrid viability (vigor)
Reduced hybrid fertility
Hybrid breakdown

13. Origin of Species Introgression
The transplantation of alleles between species.
Alleles occasionally “seep” through all reproductive barriers and pass between gene pools of closely related species. May occur when a fertile hybrid mates successfully with one of the parent species.

14. Hercules the liger
Liger
Female Ligers are fertile and can reproduce. If a Female liger mated with a male tiger the offspring would have some lion genes. If that offspring could then mate with a tiger the lion genes would continue on within the Tiger Gene Pool, an example of introgression.

15. A summary of reproductive barriers between closely related species

16. Origin of Species Modes of speciation
Allopatric speciation
A population forms a new species while geographically isolated from its parent population
Sympatric speciation
Species formation occurs in geographically overlapping populations

17. Two modes of speciation

18. Origin of Species Allopatric speciation
occurs when the initial block to gene flow is a geographical barrier that physically isolates the population.
The genetically isolated group can then follow its own evolutionary course as changes in allele frequencies occur and are undiluted by gene flow from other populations

19. Has speciation occurred during geographic isolation?

20. Allopatric speciation of squirrels in the Grand Canyon
White-tailed antelope squirrel (north rim)
Harris’s antelope squirrel (south rim)

21. Speciation in Galapagos Finches

22. Speciation in Cichlids

23. Origin of Species Allopatric speciation
Adaptive Radiation = emergence of numerous species from a common ancestor introduced into an environment.
Example: Darwin’s finches on the Galapagos island chain

24. Adaptive Radiation of Galapagos Finches

25. A model for adaptive radiation on island chains

26. Adaptive Radiation in Cichlids (Specialization in feeding)

27. Origin of Species Sympatric speciation
Formation of a new species within the geographical range of the parent population (no geographical isolation)
Can occur quickly (in one generation) if a genetic change results in a reproductive barrier between mutants and the parent population

28. Origin of Species Sympatric speciation
Iris
Polyploid speciation
Many plant species have originated from improper cell division that resulted in polypoidy
Autopolyploidy – an organism that has more than two chromosome sets, all derived from the same species
Allopolyploidy – a polyploid hybrid resulting from contributions by two different species. More common than autopolyploidy. Hybrids are usually sterile but may be very vigorous and propagate asexually.
Daylily

29. Sympatric speciation by autopolyploidy in plants

30. One mechanism for allopolyploid speciation in plants

31. Punctuated Equilibrium vs. Gradualism
Punctuated equilibrium model suggests evolution occurring in spurts of relatively rapid change instead of gradual divergence

32. Two models for the tempo of speciation