Description of species and speciation

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
Zoo @ 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:
http://www.youtube.com/watch?v=4
MPfTzXEZdY
• 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):
• http://www.lewis-clark.org/content/content-article.asp?ArticleID=401

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. 2008. Biology, 8th ed. Pearson Benjamin Cummings.