1. CHAPTER 14 The Origin of Species
Modules 14.1 – 14.2

3. Evolution Underground
Evolution has generally been thought of as a very gradual process
However, examples of rapid evolution have been observed

4. One example of rapid evolution occurred among mosquitoes who migrated into the London underground
In less than 150 years, Culex pipiens evolved into a new mosquito species, Culex molestus
The origin of new species is called speciation

5. The isolated mosquitoes adapted to their new underground environment
They altered their prey, mating habits (bred year round vs. winter hibernating above ground species), and breeding patterns
When two different mosquitoes brought together in lab, no offspring = different species.
Environmental barriers that isolate populations are just one of many mechanisms in the evolution of species

6. CONCEPTS OF SPECIES 14.1 What is a species?
Linnaeus used physical appearance to identify species when he developed the binomial system of naming organisms (Genus species = Homo sapiens)
This system established the basis for taxonomy, the naming and classifying of species.

7. But appearance alone does not always define a species
Example: eastern and western meadowlarks
They appear pretty much identical
Figure 14.1A

8. Similarities between some species and variation within a species can make defining species difficult
Humans exhibit extreme physical diversity, but we interbreed
Mosquitoes no extreme physical diversity, but no interbreeding
Figure 14.1B

9. The biological species concept defines a species as
a population or group of populations whose members can interbreed and produce fertile offspring
i.e. humans, although exhibiting considerable diversity of form

10. A ring species may illustrate the process of speciation1
OREGON
POPULATION
Sierra Nevada 2
Yellow- blotched
Yellow- eyed
INLAND POPULATIONS
COASTAL POPULATIONS
Gap in ring
Large- blotched
Monterey 3
Figure 14.1C

11. Ring species
Distribution forms a ring as it extends its range around a geographic barrier.

12. The biological species concept is not applicable to fossils or asexual organisms. So similarity of appearance, bio chemical features and fossil record are used to distinguish species.
Most organisms are classified based on observable phenotypes
The morphological species concept
The genealogical species concept defines a species as a cluster of organisms representing a specific evolutionary lineage
Uses DNA and RNA sequence data
The ecological species concept defines a species by its ecological role

14. 14.2 Reproductive barriers keep species separate
Prezygotic and postzygotic reproductive barriers prevent individuals of different species from interbreeding
Table 14.2

15. Courtship ritual in blue-footed boobies is an example of one kind of prezygotic barrier, behavioral isolation
Many plant species have flower structures that are adapted to specific pollinators
This is an example of mechanical isolation, another prezygotic barrier
Figure 14.2A, B

16. Hybrid sterility is one type of postzygotic barrier
A horse and a donkey may produce a hybrid offspring, a mule
Mules are sterile
Figure 14.2C

17. 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

18. Changes occur by microevolutionary processes
Mutation, genetic drift and natural selection
Geographic isolation
Mountain formation, deep canyons, removal of land bridges or continental drift
Barrier effectiveness depends on effective dispersal in organisms that might speciate and size of the population
Small populations more likely than large populations to develop into new species
Large animals can cross some barriers a small animal might not

19. 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

20. 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

21. Darwin finches – distinguished by morphology and habitat
Islands need to be close together or to mainland to allow for occasional dispersion but maintain mostly isolation
Darwin finches – distinguished by morphology and habitat
Cactus eaters
Seed eaters
Insect eaters
Farther island with only 1 species, compared to islands close together with multiple

22. 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

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

24. Polyploidy Extra set of chromosomes
Plants from tetraploid zygote can reproduce by self-fertilizaton but cannot produce fertile offspring by mating with diploid ancestors, due to resulting triploid offspring
Most polyploid species are result of hybridization of two species with the resulting offspring being sterile. However, the hybrid may reproduce asexually.

25. 14.6 Connection: Polyploid plants clothe and feed us
Many plants are polyploid, including oats, potatoes, bananas, peanuts, barley, plums, apples, wheat and cotton
They are the products of hybridization
The modern bread wheat is an example
Figure 14.6A

26. 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

27. 14.7 Reproductive barriers may evolve as populations diverge
This has been documented by
laboratory studies (fruit flies)
Flies more likely to breed with flies raised on same medium
Demonstrates development of reproductive barrier w/in two populations of 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

28. examples in natural populations (pupfish in Death Valley)
Each spring has unique species
Figure 14.7B

29. 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

30. 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

31. Ultimately both models have some merit, and some species evolved with a combination of these models.

32. 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