1. The Origin of Species
Chapter 16
Botany 4

2. Outline I. Introduction II. What is a species?
Anagenesis vs. cladogenesis
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. Anagenesis is change within a lineage; cladogenesis is the divergence of one lineage into two.

5. 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.

6. Reproductive Isolation and Isolating Mechanisms

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

8. ex:mule

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

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

11. Modes of Speciation

12. There are two general modes of speciation:
Allopatric - speciation takes place in populations with geographically separate ranges
Sympatric - speciation takes place in geographically overlapping populations

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

15. 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.

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

17. 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 ….

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

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

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

21. 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.