1. Species and Speciation
BIOL 1407

2. Biological Species Concept
A group of organisms that can interbreed and produce viable, fertile offspring
Photo Credit of Galápagos Marine Iguanas: Putneymark, 2008, Wikimedia Commons

3. Biological Species Concept
Assumes
Common characteristics
Genetically compatible
Interbreed under natural conditions
Sexual Reproduction
Photo Credit of Iguana iguana: Ianare, 2007, Wikimedia Commons

4. Drawbacks of Biological Species Concept
Cannot be used with exclusively asexual organisms
Prokaryotes
Amoeba & some other protists
Some animals, plants & fungi
Photo Credit of Amoeba proteus: Angel, BIOL 1407 student, fall 2008

5. Drawbacks: Isolated Populations
How do you test for interbreeding under natural conditions?
Can a deer in Florida interbreed with one in Wisconsin?
Photo Credit of Key Deer: Scott Bauer, 2006, USDA
Photo Credit of Deer Running: Paul Frank, 2006, USFWS

6. Drawbacks Can a Great Dane interbreed with a Chihuahua?
Photo Credit: David Shankbone, 2006, Wikimedia Commons

7. Drawbacks Some species look and behave differently
Can interbreed and have viable, fertile offspring
Example: coyotes, wolves, dogs
Picture Credits: Courtesy of Smithsonian National nationalzoo.si.edu (coyote and wolf); Pam Wolfe (dog)

8. Drawbacks: Horizontal Gene Transfer
Vertical gene transfer
Parents  offspring
Horizontal gene transfer
Individual  individual
Not parent-offspring
Diagram Credit: Gregorius Pilosus, 2009, Wikimedia Commons

9. Horizontal Gene Transfer
Can occur between organisms:
Different species
Different kingdoms
Different domains
Diagram Credit: Barth F. Smets, Ph.D., with permission, 2005, Wikimedia Commons

10. Horizontal Gene Transfer in Bacteria
(1) Transformation

11. Horizontal Gene Transfer in Bacteria
(2) Transduction

12. Horizontal Gene Transfer in Bacteria
(3) Conjugation

13. Horizontal Gene Transfer
E. coli 0157:H7 has picked up Shiga toxin gene from Shigella
Up to 25% genetic difference among E. coli strains
Photo Credit of E. coli 0157:H7: E. H. White, Centers for Disease Control, 1995, Wikimedia Commons

14. Horizontal Gene Transfer
Normally, 25% genetic diversity  different species
Human and chimp genomes differ by only 1.2%
Photo Credit: Thomas Lersch, 2005, Wikimedia Commons

15. Drawbacks: Fossil Species
Cannot tell if fossil organisms were capable of interbreeding
Photo Credit of Harlan’s Ground Sloth: Doyle Cross, 2006, UT Memorial Museum

16. Fossils
Normally can’t compare genes of different fossil species

17. Morphological Species Concept
Group of individuals that share common characteristics
Used for:
Fossils
Exclusively asexual
Traditional method for sexual organisms
Photo Credit of Orchid: Bernd Haynold, 2004, Wikimedia Commons

18. Biological Species Concept: Reproductive Isolation
Barriers between species
Prevent viable fertile offspring
Photo Credit (Lesser Bird of Paradise): Roderick Eime, 2005; (Greater Bird of Paradise): Andrea Lawardi, 2008, Wikimedia Commons

19. Reproductive Isolating Mechanisms
Prezygotic mechanisms
Before fertilization
Postzygotic mechanisms
After fertilization

20. Prezygotic Mechanisms
Prevents:
Prevent mating from occurring
Prevents gametes from forming a zygote
Photo Credit for Sperm fertilizing an ovum: Wikimedia Commons, 2008

21. Prezygotic Mechanisms: Temporal Isolation
Isolated by time
May breed:
Different times of day
Different seasons
Different years
Photo Credit: Alan Zomerfeld, 2006, Wikimedia Commons

22. Temporal Isolation
Late Winter
Late Summer

23. Prezygotic Mechanisms: Habitat Isolation
Same geographic area
Different habitats

24. Prezygotic Mechanisms: Behavioral Isolation
Different courtship rituals
Blue-Footed Booby Video:
Photo Credit: Richard001, 2007, Wikimedia Commons

25. Behavioral Isolation Eastern and Western Meadowlarks
Isolated by Songs
Listen to both species (Links to songs are below the picture):

26. Prezygotic Mechanisms: Mechanical Isolation
Structural differences prevent mating
Example:
Genital openings (arrows) not aligned  No Mating

27. Prezygotic Mechanisms: Gametic Isolation
Sperm cannot fertilize eggs
Very important in aquatic species (broadcast spawners)
Example: Sea Urchins

28. Postzygotic Mechanisms
Prevents hybrid zygotes from developing into viable, fertile adults
Photo Credit of Zeedonk: Ondrejk, 2004, Wikimedia Commons

29. Postzygotic Mechanism: Reduced Hybrid Viability
If Sheep and goats mate  Hybrid zygotes
Die before birth.
Photo Credit: Missouri NRCS Photo Gallery

30. Postzygotic Mechanism: Reduced Hybrid Fertility
Male donkey x Female horse Mule
Mules:
Healthy (viable)
Sterile.

31. Postzygotic Mechanism: Hybrid Breakdown
First generation hybrids are viable and fertile.
Offspring of hybrids are feeble or sterile.

32. Speciation Process of species formation Two main mechanisms:
Allopatric speciation
Sympatric speciation

33. Allopatric Speciation
Geographic separation
 Genetic exchange
Populations become genetically different
Reproductive isolation

34. Sympatric Speciation Populations not geographically separated
Can be due to rapid genetic changes:
Alter morphology
Alter behavior
Alter habitat preferences

35. Example: Sympatric Speciation
Euhadra snails
Mutation in one gene  Shell spirals in opposite direction
Instant mechanical isolation
 Two species

36. Adaptive Radiation A common ancestor  Many new species
Relatively rapid
Common in island chains
Isolated
Numerous habitats & resources
Map Credit: M. Minderhoud, 2006, Wikimedia Commons

37. Galápagos Finches
Ancestral finch from South America  Several finch species
Different diets
Different beak shapes
Different beak sizes

38. Galápagos Finches

39. Hawaiian Silverswords
Tarweed arrived from North America ~ 5 mya
Common ancestor  Silverswords
Map Credit: M. Minderhoud, 2006, Wikimedia Commons

40. Hawaiian Silverswords

41. The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al Biology, 8th ed. Pearson Benjamin Cummings.