1. Chapter 24 BCOR 012 February 8 and 10, 2010
The Origin of Species
Chapter 24
BCOR 012
February 8 and 10, 2010

2. Outline for February 08, 2010: I. Introduction II. What is a species?
The biological species concept
Reproductive isolating mechanisms
Alternative species concepts
III. Modes of speciation
Allopatric
Sympatric
the tempo of change

3. What is a species?

4. The Biological Species Concept
The biological species concept defines a species as a population or a series of populations whose members have the potential to interbreed and which are reproductively isolated from other such populations.

5. Reproductive Isolation and Isolating Mechanisms

6. ex. fireflies
Biologists distinguish between prezygotic and postzygotic isolating mechanisms.

7. ex:mule

8. Limitations of the BSC:
Not applicable to asexually reproducing organisms
Useless with respect to the fossil record

9. Alternative species concepts:
Ecological species concept - defines a species in terms of its ecological niche
Morphological species concept - emphasis is on unique structural features
Phylogenetic species concept - emphasis is on ancestor-descendent relationships
Pluralistic species concept - acknowledges that, where species concepts are concerned, one size may not fit all!

10. Modes of Speciation

11. There are two general modes of speciation:
Allopatric (other homeland)- speciation takes place in populations with geographically separate ranges
Sympatric (same homeland) - speciation takes place in geographically overlapping populations

12. Allopatric speciation of antelope squirrels in the Grand Canyon
Ammospermophilus harrisi
Ammospermophilus leucurus S N
Allopatric speciation of antelope squirrels in the Grand Canyon

14. In allopatric speciation, a new species originates while geographically isolated from its ancestor. As the new species evolves by genetic drift and natural selection, reproductive isolation from the ancestral
species may evolve as a by-product of genetic change.

15. Sympatric speciation - a mode in
which a new species arises in the
geographic midst of its progenitor
species.

16. In plants, sympatric species may arise by polyploidy
a condition that results in extra sets of chromosomes
in the derivative species.
An example from the European holly ferns ….

17. European holly
ferns
(Polystichum)
P. setiferum
P. lonchitis
P. aculeatum

18. The origin of European Polystichum aculeatum
P. aculeatum
(4X)
primary diploid
hybrid
P. setiferum
P. lonchitis
(2X)
(2X)

19. The origin of European Polystichum aculeatum
P. aculeatum
primary diploid
hybrid
P. setiferum
P. lonchitis
P. setiferum n=41

20. Sympatric speciation in animals -
East African Cichlids
(sick-lids)

21. Pundamilia pundamilia
Pundamilia nyererei
a) Normal light
b) Monochromatic orange light
Non-random mating, in which females select mates having a preferred appearance, is the main reproductive barrier keeping these two species separate in nature. This is an example of sympatric speciation in response to sexual selection.

22. Sympatric speciation requires the emergence of some sort of reproductive barrier that isolates the gene pool of a population subset without geographic separation from the parent population.

23. Hybrid Zones

27. The Tempo of Evolution

28. Punctuated equilibrium: instead of a slow, continuous movement, evolution tends to be characterized by long periods of virtual standstill ("equilibrium"), "punctuated" by episodes of very fast development of new forms.

29. A fabulous lesson on punctuated equilibrium ...

30. Anagenesis is change within a lineage; cladogenesis is the divergence of one lineage into two.