1. 15.2 Species and Speciation Overview
Evolution
Results of evolution
New species (speciation)
Causes of evolution
Barriers between same species (gene pools)
Geographical isolation -> leads to allopatric speciation
Temporal isolation -> leads to sympatric speciation
Behavioral isolation -> leads to sympatric speciation
Hybridization -> leads to sympatric speciation
Types of Evolution
Adaptive radiation
Convergent evolution
Divergent evolution
Pace of Evolution
Gradualism
Punctuated equilibrium

2. Gene pool – all of the genetic information present in the reproducing members of a population at a given time
A large gene pool exists in a population which shows high variation
A small gene pool exists in a population which shows little variation (ex: inbreeding)

3. Allele frequency – measure of the proportion of a specific variation (allele) of a gene in a population; this can be stated as a proportion or a percent
Remember, Hardy-Weinberg discussed this in terms of p and q where:
p = frequency of the dominant allele
q = frequency of the recessive allele
and together p + q = 1
If there are no changes in allele frequency over time, then no evolution
If there is big change in allele frequency over time, evolution has occurred

4. Review of what can change allele frequencies (and therefore the gene pool) within a population:
Mutations
Immigration and emigration
Nonrandom mating (ex: inbreeding/selective breeding)
Some alleles are more advantageous than other alleles
The population is small and therefore the allele frequencies are easier to manipulate

5. Species – the basic unit for classifying an organism
A species is made up of organisms which:
Have the ability to interbreed and produce fertile offspring
Share the same ecological niche
Have the same karyotypes
Have a common phylogeny (share common ancestor(s))
Share a unique collection of structural and functional characteristics

6. Barriers between Gene Pools
Barriers may exist where populations of members of the same species can be stopped from reproducing together; such barriers can be geographical, temporal, behavioral, or related to infertility caused by hybridization
This slide is an overview of what is to come, no need to write it down!

8. Allopatric Speciation
When a new species forms from an existing species due to a geographic barrier

9. 1. Geographical Isolation
Type of Allopatric Speciation!
Occurs when physical barriers such as land or water formations prevent mating
Ex: tree snails in Hawaii, 1 population lives on trees on one side of a volcano, the other population lives on trees on the other side of the volcano

10. Sympatric Speciation
When a new species is formed from an existing species while living in the same geographic area
This is much rarer than allopatric speciation

11. Type of Sympatric Speciation
1. Temporal Isolation
Type of Sympatric Speciation
Occurs when two populations mate or flower at different times of the year
Ex: the female parts of one flower’s population reach maturity before the pollen of another flower’s population gets released
Ex: one population of mammals is still hibernating while another population is ready to mate

12. Type of Sympatric Speciation
2. Behavioral Isolation
Type of Sympatric Speciation
Occurs when one population’s lifestyle and habits are not compatible with those of another population
Ex: many birds rely on courtship displays to attract mates; if one population has a version of the courtship display which is significantly different from another population, they may not consider each other to be seductive enough to mate with

13. 3. Hybrids
Hybrids are typically infertile and therefore cannot pass on their karyotype
This goes for plants and animals
female horse + male donkey = mule
male horse + female donkey = hinny
female tiger + male lion = liger
male tiger + female lion = tigon

14. How polyploidy leads to speciation:
Speciation is when a population evolves significantly enough so that the production of offspring with the original population becomes impossible
Haploid – sex cells are monoploidy (n)
Diploid – somatic cells are diploidy (2n)
Polyploidy = more than 2 sets of chromosomes; 3n, 4n, 5n, ect.
Ploidy changes among angiosperms are common including banana tree, tobacco plant, apple trees
Also seen in animal kingdom with salamanders, frogs, and leeches

15. Studies have shown after polyploidy formation rapid changes in gene structure and expression can occur; if one population evolves enough to have significant change, then a new species can be formed
NOTE: two similarly polyploidy organisms can interbreed ex: 8n sugar cane with another 8n sugar cane

16. Adaptive Radiation
It is when many similar but distinct species evolve relatively rapidly from a single species or from a small number of species
These organisms will
share homologous
structures with various
functions
Occurs due to variation,
natural selection, and
the exploitation of
various niches

17. Lemurs of Madagascar
Lemurs were able to survive (no other primates present) and adaptive radiation allowed them to fill all the islands niches
On ground
In trees
In desert
In rainforest

18. Divergent Evolution
Divergent evolution is where organisms have a common ancestor, but have become more different as time goes by
Example:
The pentadactyl limb – the homologous structure in many vertebrates including the human arm, the fin of a whale, and the wing of a bird

19. Convergent Evolution
Convergent evolution is where distantly related organisms evolve similar traits as they adapt to similar environments; they become more alike
Example:
Marsupials and placental organisms evolved separately on different continents, but both types evolved into all the niche of the area

20. In both types of evolution, it is the process of natural selection that allowed the organisms to adapt to their environments in the ways that they did

21. The Pace of Evolution
Gradualism – the idea that evolution occurs over small, continuous, and slow changes
First proposed in late 1700’s and was adopted by Darwin
Supporters argue:
fossil record shows a succession of small changes that is steady and ongoing
must be gradual since we don’t witness it

23. Discuss ideas on the pace of evolution:
Punctuated equilibrium – the idea that evolution occurs relatively quickly and is followed by long periods of little or no change
Theory developed 1900’s
Supporters state
speciation happens quickly, often in response to environmental changes
fossils of animals like sharks and cockroaches show little change thru time

25. Problems with Either Arguments
Only evidence we can use is fossil evidence; can’t use characteristics such as pigmentation, behavior, mating calls/songs
Just b/c a fossil looks like a modern day organism, doesn’t mean they are related

26. Describe one example of transient polymorphism
Polymorphisms – different versions of a species
This Virginia Springbeauty flower shows polymorphism with its flower color

27. Transient polymorphism – where two or more forms of a species exist in the same population; it results in one form dominating the other form; can be result of mutation
Ex: peppered moth
Peppered form
Melanic form

28. The phenomenon of factory pollution changing the population of peppered moths is called Industrial melanism. Shows how natural selection works in nature and no one trait is always good or bad Transient because the results can change over time

29. For sickle cell (homozygous recessive):
Balanced polymorphism – when the two different forms in a species are not changing, but are stabilized by natural selection
Ex: sickle cell
For sickle cell (homozygous recessive):
AA = normal red blood cells, susceptible to malaria
AS = normal and sickle blood cells, some resistance to malaria
SS = sickle-shaped blood cells, highly resistant to malaria
Due to the benefit of the sickle cell allele against malaria, the presence of the sickle allele is relatively stable and shows balanced polymorphism; one side shows pressure towards the allele, the other side shows pressure against the allele