1. Speciation

2. Speciation
The formation of a new species from pre-existing species.

3. What is a species?
A population of physically similar organisms that can interbreed and produce fertile offspring
fertile= able to produce more offspring
Are these spiders the same species?
Happy Face Spiders – although different are the same species

4. Same Species? Horse + Donkey = Mule=
Horse Donkey = Mule
Mules are sterile – unable to reproduce
Conclusion: Horses and Donkeys are different species
Chromosomes are similar enough to produce offspring but too different to produce a fertile offspring

5. Limits to Species Definition
Impossible to test reproductive compatibility of extinct organisms
Some organisms reproduce asexually- they don’t interbreed
bacteria-reproduce asexually by binary fission
bacteria produced by binary fission are genetically identical to one another

6. How do species form? Speciation requires isolation
2 parts of a population that interbreed are prevented from interbreeding

7. Two Types of Isolation Geographic –
A physical barrier separates formerly interbreeding members of a population
Example- Desert Pupfish
13 species of small fish in Southwest US.

8. Geographic Isolation Continued
Area was once covered in a large lake during the last ice age
-ice age ended – lake dried up
-small populations of pupfish were isolated in small spring fed lakes-
- lakes selected different phenotypes – led to new species

9. Reproductive Isolation
Behavioral or physical differences that prevent members of a population from interbreeding

10. Reproductive Isolation
Wood Frogs and Leopard frogs very closely related, but different mating calls and mating times prevent interbreeding

11. Reproductive Isolation continued
Eastern and Western Meadow Larks-nearly identical,only hybridize at the edge of their range

12. Genetic drift

16. How do we track speciation?