1. CHAPTER 14 The Origin of Species
Modules 14.3 – 14.9

2. 14.3 Geographic isolation can lead to speciation
MECHANISMS OF SPECIATION
14.3 Geographic isolation can lead to speciation
When a population is cut off from its parent stock, species evolution may occur
An isolated population may become genetically unique as its gene pool is changed by natural selection, genetic drift, or mutation
This is called allopatric speciation
Figure 14.3

3. 14.4 Islands are living laboratories of speciation
On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches
Figure 14.4A

4. Adaptive radiation on an island chain1
Species A from mainland 2 B A B 3 B B 4 C C C C D C D 5
Figure 14.4B

5. Unreduced diploid gametes
14.5 New species can also arise within the same geographic area as the parent species
In sympatric speciation, a new species may arise without geographic isolation
A failure in meiosis can produce diploid gametes
Self-fertilization can then produce a tetraploid zygote
Parent species
Zygote
Meiotic error
Self- fertilization
Offspring may be viable and self-fertile
2n = 6 Diploid
4n = 12 Tetraploid
Unreduced diploid gametes
Figure 14.5A

6. Sympatric speciation by polyploidy was first discovered by Dutch botanist Hugo de Vries in the early 1900s
Figure 14.5B

7. 14.6 Connection: Polyploid plants clothe and feed us
Many plants are polyploid
They are the products of hybridization
The modern bread wheat is an example
Figure 14.6A

8. The evolution of wheat AA BB Wild Triticum (14 chromo- somes)
Triticum monococcum (14 chromosomes) AB
Sterile hybrid (14 chromosomes)
Meiotic error and self-fertilization
AABB DD
T. turgidum EMMER WHEAT (28 chromosomes)
T. tauschii (wild) (14 chromosomes)
ABD
Sterile hybrid
Meiotic error and self-fertilization
AA BB DD
T. aestivum BREAD WHEAT (42 chromosomes)
Figure 14.6B

9. 14.7 Reproductive barriers may evolve as populations diverge
This has been documented by
laboratory studies (fruit flies)
Initial sample of fruit flies
Starch medium
Maltose medium
Results of mating experiments
Female populations
Female
Starch
Maltose
Same
Different
Starch
Same 22 9 18 15
Male populations
Male
Maltose 8 20 12 15
Different
Mating frequencies in experimental group
Mating frequencies in control group
Figure 14.7A

10. examples in natural populations (pupfish in Death Valley)
Figure 14.7B

11. 14.8 The tempo of speciation can appear steady or jumpy
According to the gradualist model of the origin of species
new species evolve by the gradual accumulation of changes brought about by natural selection
However, few gradual transitions are found in the fossil record
Figure 14.8A

12. The punctuated equilibrium model suggests that speciation occurs in spurts
Rapid change occurs when an isolated population diverges from the ancestral stock
Virtually no change occurs for the rest of the species’ existence
Figure 14.8B

13. 14.9 Talking About Science: Peter and Rosemary Grant study the evolution of Darwin’s finches
The occasional hybridization of finch species adds to the genetic variation of parent populations
This may have been important in the adaptive radiation of finch species
Figure 14.9