1. Option D:
Evolution
D2: Species and
Speciation

2. D 2.1 Define allele frequency and gene pool.
gene pool – sum of all the genes of all the individuals in a population including all the alleles for all the genes present in the population
allele frequency – the percentage of a specific allele of a given gene locus in the population

3. D 2.2 State that evolution involves a change in allele frequency in a population’s gene pool over a number of generations.
evolution of populations is best understood in terms of allele frequencies
if the allele frequencies remain constant from generation to generation, then the population is not undergoing any evolutionary change and is in genetic equilibrium
evolution can be defined as changes in gene frequencies that occur in a gene pool over time (change in the genetic makeup of populations over time)

4. Biological species concept
D 2.3 Discuss the definition of the term species.
Biological species concept
defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
reproductively compatible
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark

5. Species are created by a series of evolutionary processes
D 2.4 Describe three examples of barriers between gene pools.
Species are created by a series of evolutionary processes
populations become isolated
geographically isolated
reproductively isolated
isolated populations evolve independently

6. PRE-reproduction barriers
D 2.4 Describe three examples of barriers between gene pools.
PRE-reproduction barriers
- obstacle to mating or to fertilization if mating occurs
geographic isolation
ecological isolation
temporal isolation
behavioral isolation
mechanical isolation
gametic isolation

7. Species occur in different areas
D 2.4 Describe three examples of barriers between gene pools.
Geographic isolation
Species occur in different areas
physical barrier
allopatric speciation
“other country”
Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

8. D 2.4 Describe three examples of barriers between gene pools.
Ecological isolation
Species occur in same region, but occupy different habitats so rarely encounter each other
reproductively isolated
2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial
lions & tigers could hybridize, but they live in different habitats:
lions in grasslands
tigers in rainforest

9. D 2.4 Describe three examples of barriers between gene pools.
Temporal isolation
Species that breed during different times of day, different seasons, or different years cannot mix gametes
reproductive isolation
sympatric speciation
“same country”
Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

10. D 2.4 Describe three examples of barriers between gene pools.
Behavioral isolation
Unique behavioral patterns & rituals isolate species
identifies members of species
attract mates of same species 
courtship rituals, mating calls
reproductive isolation
The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown.
The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky.
Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about.
Blue footed boobies mate only after a courtship display unique to their species

11. Recognizing your own species
courtship songs of sympatric species of lacewings
courtship display of Gray-Crowned Cranes, Kenya
firefly courtship displays

12. Plants Mechanical isolation
D 2.4 Describe three examples of barriers between gene pools.
Mechanical isolation
Morphological differences can prevent successful mating
reproductive isolation
Plants
Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.
Mimulus ( /ˈmɪmjuːləs/)[1] is a diverse plant genus, the monkey-flowers and musk-flowers. Mimulus are called monkey-flowers because some species have flowers shaped like a monkey's face,[3] others have painted faces resembling a monkey. The generic name, Latin mimus meaning "mimic actor", from the Greek mimos meaning "imitator" also references this. Some species produce copious amounts of aromatic compounds, giving them a musky odor (hence "musk-flowers").

13. Animals Mechanical isolation
D 2.4 Describe three examples of barriers between gene pools.
Mechanical isolation
Animals
For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer
lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals!
The selection is intense because it directly affects offspring production -- it is affecting sex itself
I can’t even imagine!

14. D 2.4 Describe three examples of barriers between gene pools.
Gametic isolation
Sperm of one species may not be able to fertilize eggs of another species
biochemical barrier so sperm cannot penetrate egg
receptor recognition: lock & key between egg & sperm
chemical incompatibility
sperm cannot survive in female reproductive tract
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

15. POST-reproduction barriers
D 2.4 Describe three examples of barriers between gene pools.
POST-reproduction barriers
Prevent hybrid offspring from developing into a viable, fertile adult
reduced hybrid viability
reduced hybrid fertility
hybrid breakdown
zebroid
liger

16. Reduced hybrid viability
D 2.4 Describe three examples of barriers between gene pools.
Reduced hybrid viability
Genes of different parent species may interact & impair the hybrid’s development
Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

17. Reduced hybrid fertility
D 2.4 Describe three examples of barriers between gene pools.
Reduced hybrid fertility
Even if hybrids are vigorous, they may be sterile
chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes
Mules are vigorous, but sterile
What’s wrong with having 63 chromosomes?
Odd number! Cannot pair up in meiosis.
Horses have 64 chromosomes
(32 pairs)
Donkeys have 62 chromosomes
(31 pairs)
Mules have 63 chromosomes!

18. D 2.4 Describe three examples of barriers between gene pools.
Hybrid breakdown
Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile
In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.
On path to separate species.

19. changes in chromosome number may cause instantaneous speciation
D 2.5 Explain how polyploidy can contribute to speciation.
changes in chromosome number may cause instantaneous speciation
polyploidy – common speciation mechanism in plants – possession of more than two sets of chromosomes
may occur when a fertilized egg duplicates its chromosomes but does not divide into two daughter cells – all subsequent divisions may be normal and all cells are now tetraploid

20. D 2.5 Explain how polyploidy can contribute to speciation.
caused by nondisjunction – chromosomes do not separate completely/equally
most tetraploid plants are healthy and vigorous and can go through meiosis
gametes produced can only fuse with other gametes from tetraploid plants –
cannot fuse with
gametes from original
parents
occurs in plants because
plants can self-fertilize
or reproduce asexually

21. D 2.5 Explain how polyploidy can contribute to speciation.
Autopolyploids (auto= self) are polyploids with multiple chromosome sets derived from a single species
Autopolyploids form following fusion of 2n gametes

22. D 2.5 Explain how polyploidy can contribute to speciation.
Autopolyploidy can be induced in plants using colchicine, a chemical extracted from the autumn crocus.
Autopolyploids with odd ploidys eg. triploid or
pentaploid have trouble reproducing sexually
That does not stop them from being good crops if they can be propagated asexually
Polyploidy can be induced with colchicine, an alkaloid of the meadow saffron (Colchicum autumnale) that inhibits mitosis. It hampers the development of the nuclear spindle. A mitosis that takes place after treatment with colchicin is called a C-mitosis. Since autoploids contain more than two homologous chromosomes, meiosis results in the formation of univalents and multivalent, unlike in diploids where bivalents are usually formed (Acquaah, 2007). For instance during meiosis, autotetraploids may form bivalents, quadrivalents and univalents (Fig 5.6). The ratio of these gametes following meiosis determines the fertility of a polyploid individual. Univalents and trivalents result in non-functional sterile gametes and are the most common in triploids, making them sterile.

23. + = D 2.5 Explain how polyploidy can contribute to speciation.
Allopolyploids (allo= different) come about when a sterile F1 hybrid doubles all of its chromosomes and becomes fertile.
For example, Triticale is the hybrid of wheat (Triticum turgidum) and rye (Secale cereale). It combines sought-after characteristics of the parents, but the initial hybrids were sterile until doubling of the number of chromosomes occurred
For example, Triticale is the hybrid of wheat (Triticum turgidum) and rye (Secale cereale). It combines sought-after characteristics of the parents, but the initial hybrids were sterile until doubling of the number of chromosomes occurred + =
Triticale (× Triticosecale), (/trɪtɪˈkeɪliː/) is a hybrid of wheat (Triticum) and rye (Secale) first bred in laboratories during the late 19th century. The grain was originally bred in Scotland and Sweden. Commercially available triticale is almost always a second generation hybrid, i.e., a cross between two kinds of primary (first cross) triticales. As a rule, triticale combines the high yield potential and good grain quality of wheat with the disease and environmental tolerance (including soil conditions) ofrye. Only recently has it been developed into a commercially viable crop. Depending on the cultivar, triticale can more or less resemble either of its parents. It is grown mostly for forage or fodder, although some triticale-based foods can be purchased at health food stores or are to be found in some breakfast cereals.
When crossing wheat and rye, wheat is used as the female parent and rye as the male parent (pollen donor). The resulting hybrid is sterile, and must be treated with colchicine to induce polyploidy and thus the ability to reproduce itself.
Wheat Rye Triticale

24. Species are created by a series of evolutionary processes
D 2.6 Compare allopatric and sympatric speciation.
Species are created by a series of evolutionary processes
populations become isolated
geographically isolated
reproductively isolated
isolated populations evolve independently
Isolation
allopatric
geographic separation
sympatric
still live in same area

25. Adaptive Radiation D 2.7 Outline the process of adaptive radiation.
 When a species gives rise to many new species in a relatively
short period of time
 Typically occurs when populations
of a single species invade
a variety of new habitats and
evolve in response to the
differing environmental selection
pressures

26. D 2.7 Outline the process of adaptive radiation.
Think Darwin’s finches (AGAIN!)
They originated from a population of an ancestral species that flew or were blown to the Galapagos islands from mainland South America.
They colonized the islands and (while geographically isolated) evolved via natural selection to have beaks that suited the types of food available on their islands.
Their beaks are homologous structures in that they have evolved from a common structure to have different functions.
Insect eaters
Bud eater
Seed eaters
Cactus
eater
Warbler
finch
Tree finches
Ground finches

27. Seed eaters Flower eaters Insect eaters Adaptive radiation
D 2.7 Outline the process of adaptive radiation.
Seed eaters
Flower eaters
Insect eaters
Rapid speciation: new species filling new niches, because they inherited successful adaptations.
Adaptive radiation

28. Darwin’s finches Differences in beaks
D 2.7 Outline the process of adaptive radiation.
Darwin’s finches
Differences in beaks
associated with eating different foods
survival & reproduction of beneficial adaptations to foods available on islands
Warbler finch
Woodpecker finch
Small insectivorous
tree finch
Large
insectivorous
Vegetarian
Cactus finch
Sharp-beaked finch
Small ground
finch
Medium ground finch
Large ground finch
Insect eaters
Bud eater
Seed eaters
Cactus
eater
Warbler
Tree finches
Ground finches

29. Darwin’s finches Darwin’s conclusions
D 2.7 Outline the process of adaptive radiation.
Darwin’s finches
Darwin’s conclusions
small populations of original South American finches landed on islands
variation in beaks enabled individuals to gather food successfully in the different environments
over many generations, the populations of finches changed anatomically & behaviorally
accumulation of advantageous traits in population
emergence of different species

30. Convergent evolution describes evolution towards similar traits in
D 2.8 Compare convergent and divergent evolution.
Convergent evolution describes
evolution towards similar traits in
unrelated species.
Other (random!) examples include:
Penguins in the southern hemisphere and Auks in the northern hemisphere both use wings as flippers
Echolocation in bats, toothed whales and shrews to capture prey.
Flight/gliding in birds, pterosaurs, bats, insects and flying fish!
Little Auk
Little Penguin

31. D 2.8 Compare convergent and divergent evolution.
Features that come about by convergent evolution are known as analogous structures

32. Divergent evolution describes evolution towards different traits
D 2.8 Compare convergent and divergent evolution.
Divergent evolution describes
evolution towards different traits
in closely related species.
Divergent Evolution is another way of saying adaptive radiation (D.2.7). As natural selection acts on two or more species that have arisen from a common ancestor, they become phenotypically different.

33. D 2.8 Compare convergent and divergent evolution.
It gives rise to homologous structures, features that now look different or have a different purpose for each species that has evolved

34. Gradualism Gradual divergence over long spans of time
D 2.9 Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.
Gradualism
Gradual divergence over long spans of time
assume that big changes occur as the accumulation of many small ones

35. Punctuated Equilibrium
D 2.9 Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.
Punctuated Equilibrium
Rate of speciation is not constant
rapid bursts of change
long periods of little or no change
species undergo rapid change when they 1st bud from parent population
Time

36. The periods of stasis may be explained by stabilizing selection.
D 2.9 Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.
Revisiting the tree for punctuated equilibrium it should be noted that the “sudden” speciation events are only sudden in terms of geological time. They would still take many generations and possibly thousands of years.
The periods of stasis may be explained by stabilizing selection.
The punctuation could be explained by
directional selection or disruptive selection.

37. D 2.9 Discuss ideas on the pace of evolution, including gradualism and punctuated equilibrium.
The downward facing arrows indicate selection pressure against individuals with that morphology
All images CC Andrew Colvin
Before
After
Stabilizing
Directional
Disruptive

38. Transient Polymorphism
D 2.10 Describe one example of transient polymorphism.
Polymorphism is the existence of two or more different forms of a species (Poly = “many”; morphism = “shapes”)
Transient Polymorphism
temporary change in allele frequency
ex: peppered moth melanism
Prior to 1840 peppered moths in Britain were light grey with dark spots to blend in with the grey lichen that grew on the trees in their habitat

39. D 2.10 Describe one example of transient polymorphism.
The first dark variant was reported in 1848 and by 1895 most of them were black.
The term industrial melanism was coined.
Soot and acid rain from the burning of coal changed the colour or the trees that the moths rested on.
Directional selection did the rest.

40. D 2.10 Describe one example of transient polymorphism.
Before long the majority were dark.
This situation reversed after 1956 when Britain instituted the clean air act. Less coal was burnt and most trees returned to their original colour.
Now in polluted areas most moths are dark and in rural areas most moths are light.
They are not distinct species because they still interbreed.
The theory that natural selection due to predation was the cause of these changes has been confirmed experimentally by
Dr HBD Kettlewell

41. Balanced Polymorphism
D 2.11 Describe sickle cell anemia as an example of balanced polymorphism.
Balanced Polymorphism
•Two alleles are maintained in stable equilibrium
•Heterozygote has selective advantage
Sickle cell anaemia occurs when a single-base mutation in the gene that codes for haemoglobin causes the amino acid valine to be produced in a particular spot rather than glutamic acid.

42. D 2.11 Describe sickle cell anemia as an example of balanced polymorphism.
Valine is non-polar, unlike glutamic acid, and this causes the mutant variety of haemoglobin (haemoglobin S) to crystallise at low concentrations of oxygen.
This in turn pulls the red blood cell into a sickle shape. It is less able to carry oxygen and can get stuck in small capillaries, causing blockages, pain and damage.
Homozygous individuals (HbS HbS) are
subject to a debilitating condition and have
a shortened life expectancy

43. D 2.11 Describe sickle cell anemia as an example of balanced polymorphism.
On the brighter side, while individuals who are heterozygous (HbA HbS) will have some mutant haemoglobin. They can lead normal lives. As a benefit, they are resistant to malaria as the plasmodium parasite that causes it is not able to use sickle cells to reproduce.
Individuals that are homozygous normal (HbA HbA) have no sickle cells and no resistance to malaria.
Distribution of the sickle cell trait
Historical distribution of malaria

44. Heterozygous: Sickle cell trait 50% chance Homozygous: Sickle Anaemia
‘Normal’ S A
HbA HbA
Haemoglobin: Normal
RBCs: Normal
O2 Capacity: Normal
Malaria resistance: None
HbA HbS
Haemoglobin:
50% normal, 50% mutant
RBCs: Usually normal, sickle when [O2] low
O2 Capacity: Mild anaemia
Malaria resistance: Moderate
HbS HbS
Haemoglobin: mutant
RBCs: Sickle
O2 Capacity: Severe anaemia
Malaria Resistance: High

45. D 2.11 Describe sickle cell anemia as an example of balanced polymorphism.
People who are homozygous for sickle cell are severely anemic and have less chance of surviving to reproduce.
Likewise individuals homozygous for normal hemoglobin are likely to contract malaria and are less likely to survive.
Heterozygous individuals have what is termed heterozygote advantage. They are the most likely to survive and reproduce.
Therefore both alleles are maintained in the population