1. Evolution and its processes
Chapter 11

2. Evidence of Evolution
Evolution of a population is observable in the field and in the laboratory
Guppies
Adult male guppies exhibit genetically determined spots
Juvenile and female guppies lack spots
Male and female guppies from genetically diverse populations were collected from different mountain streams and placed together in an isolated environment containing no predators

3. Evidence of Evolution
Evolution of a population is observable in the field and in the laboratory
Guppies
The population was maintained for several generations
Separated into two groups: one with a predator and one without a predator
Each group was maintained through several generations
Throughout the experiment, the mean number of spots per adult male guppies was determined

4. What happens to the mean number of spots during the first 6 months?
What do the bars going through each point represent?
What happens to the genetic variation during the first 6 months?
What is a possible explanation for the changes?

5. What happens to the mean number of spots in the group with the predator?
What happens to the mean number of spots in the group without the predator?
What is a possible explanation for the differences?

6. Species and Speciation
A species is a distinct group
Morphologically different from other groups
Do not interbreed with other groups
Reproductively isolated

7. Species and Speciation
Speciation is the formation of new species
A population is divided into subpopulations
Subpopulations are reproductively isolated
Natural selection, genetic drift, and mutations can occur differently in each subpopulation
Evolution takes a different course in each subpopulation
After a long period of time this may result in two different species

8. Species and Speciation
Reproductive Isolation
The end of gene flow between populations
Always a part of speciation

9. Species and Speciation
Reproductive Isolation Mechanisms
Temporal isolation
Individuals reproduce at different times
Cicadas: different reproductive cycles (13 verses 17 year)

10. Species and Speciation
Reproductive Isolation Mechanisms
Mechanical isolation
Physical incompatibilities prevent interbreeding
Black sage and white sage: specialized for different pollinators
Black sage flowers are small and delicate. It is pollinated mainly by honeybees and other small insects
White sage pollen coated anthers are too far away from the petals to be brushed by smaller insects. Larger bees and hawkmoths are the pollinators.

11. Species and Speciation
Reproductive Isolation Mechanisms
Ecological isolation
Adapted to different microenvironments in the same region
Two species of manzanita: One is drought-adapted, the other is not

12. Species and Speciation
Reproductive Isolation Mechanisms
Behavioral Isolation
Bird courtship displays

13. Species and Speciation
Reproductive Isolation Mechanisms
If mating occurs…
Gamete incompatibility
Molecular signals are species specific
Hybrid inviability
Chromosome and gene differences
Hybrid sterility
Horse X donkey = sterile mule

14. Species and Speciation
Speciation can occur in three different ways
Each requires some mechanism to ensure reproductive isolation

15. Species and Speciation
Allopatric Speciation (with geographic isolation)
Subpopulations become geographically isolated, thus reproductively isolated

16. Figure 17. 20 Allopatric speciation in snapping shrimp
Figure Allopatric speciation in snapping shrimp. The Isthmus of Panama (above) cut off gene flow among populations of these aquatic shrimp when it formed 4 million years ago. Today, individuals from opposite sides of the isthmus are so similar that they might interbreed, but they are behaviorally isolated: Instead of mating when they are brought together, they snap their claws at one another aggressively. The photos on the right show two of the many closely related species that live on opposite sides of the isthmus.
Fig , p. 272

17. Species and Speciation
Sympatric Speciation (without geographic isolation)
Within the same population some individuals are reproductively isolated
Plants
Change in chromosome number
Here we see two species of anemone flower and their chromosomes. Changes in number of chromosomes, as has occurred in this genus, can cause speciation.

18. Species and Speciation
Sympatric Speciation (without geographic isolation)
Within the same population some individuals are reproductively isolated
Indigobirds are brood parasites
Young learn the song of the host species
More likely to mate with birds that learned the same song
Ciclids
Females choose mate based on colors she perceives

19. Species and Speciation
Parapatric Speciation (without geographic isolation)
Small local populations are more likely to breed within their immediate population than with another local population (new niche formed)
Sea urchins in a tidepool
Velvet walking worms
Although continuously distributed, different flowering times have begun to reduce gene flow between metal-tolerant plants and metal-intolerant plants.

22. Summary Observations of nature changed our thinking
Change over time /natural selection/evolution
Hardy-Weinberg Equation
Populations evolve
Mechanisms
Genetic drift, gene flow, mutation, natural selection
Species and Speciation

23. Early Evolutionary Concepts
Count de Buffon ( )
Described all known plants and animals (44 volumes)
Observed structural variations in particular organs of related animals
Believed in a special creation and considered change as being degenerate
Apes = degenerate humans
Provided no theories on how change/degeneration might take place

24. Change over Time Charles Lyell
Gradual geological processes sculpted Earth’s current landscape over great spans of time
Challenged the prevailing belief of the age of Earth
Thomas Malthus
Economist that correlated increases in the size of human populations with episodes of famine, disease, and war
Humans reproduce beyond the capacity of their environment
Must compete for limited resources or develop technology to increase productivity