Evolution: Lecture 2

Question 1

Examples of natural selection?

Answer 1

• Drug resistance in pathogenic microorganisms (cause disease)
• Pesticide resistance
• Host-switching in insects (feed on plants and go from one to another)

Question 2

Are these the only systems where we observe natural selection?

Answer 2

No, we can see many other systems that have natural selection in them.

• These are just more convenient systems to study for biologists.

Question 3

Why are they more convenient?

Answer 3

They are more convenient due to:

• Strong selective pressure (more resistant populations)
• Short generation times as they are easier for longevity (one biologist can carry out the entire study).

Question 4

What is selective pressure?

Answer 4

A selective pressure is any reason for organisms with certain characters to have either a survival benefit or disadvantage.

Question 5

Example of selective pressure?

Answer 5

People with darker skin have an advantage in the sun when compared to people with lighter skin.

Question 6

What is warfarin and when was it done?

Answer 6

Warfarin is a rat poison (pesticide) that has been used since the 1950’s, being laced into rat baits.

Question 7

What does Warfarin do?

Answer 7

Warfarin interferes with synthesis of
blood-clotting agents which causes bleeding which causes death.

• A few days after exposure, there are no blood clotting factors left.

Question 8

Effect of Warfarin?

Answer 8

A small cut or spontaneous bleed will cause the rat to bleed out and die.

Question 9

What is Warfarin actually doing?

Answer 9

It is interfering with and enzyme that regenerates inactive K vitamins, which are used to produce blood clotting agents.

• Vitamin K is used up then regenerated in the process of making blood clotting agents but they cannot work without the enzyme which is impacted by warfarin.

Question 10

What is associated with warfarin resistance?

Answer 10

Mutation(s) in a gene that encodes VKORC1 are associated with warfarin resistance.

Question 11

What does this mutation in VKORC1 actually do?

Answer 11

The mutation makes an amino acid change that blocks the effect of warfarin, therefore only a higher dose will do damage to the rat.

• This is associated with increased warfarin resistance.
• There is a lower chance of a resistant rat consuming a high enough dose to become sick.

Question 12

How does resistance increase?

Answer 12

Resistance increases rapidly in populations after poisoning programs were introduced.

• Poison works well at first but quickly resistance will increase.

Question 13

Why does resistance increase so fast?

Answer 13

A much larger proportion can become tolerant because resistant rats can have more children (more fitness = more offspring).

Question 14

What do we see from the graph showing poison resistance?

Answer 14

When the poison was introduced, the percentage of resistant rats climbed extremely quickly. After it was taken away, however, the percentage of resistant rats decreased once again.

Question 15

Why did resistance go down after the poison was taken away?

Answer 15

It went down because it is less advantageous be resistant when there is no poison present in the environment.

Question 16

Health of resistant rats vs. susceptible rats?

Answer 16

When there is no poison present, resistant rats are less healthy than the susceptible rats, who are extremely healthier.

Question 17

How many effects are there to the mutation?

Answer 17

The mutation has two effects:

1. relatively resistant to warfarin
2. poor user of vitamin K

Question 18

What features of natural selection does this example demonstrate?

Answer 18

1. Editing rather than creative mechanism. The variation must simply be acted on not created
   – Needs variation to act on
2. Contingent on time and place
   (adaptation to the particular environment). The gene variants that confer warfarin resistance happen to be disadvantageous when poison is not being used. This is why the percentage goes down after the poison is taken away.

Question 19

What are soapberry bugs?

Answer 19

They are bugs with beaks that they insert into the fruit to extract food. Their typical fruit is from the balloon vine tree, accounting for their long beaks. Yet, in some areas, a tree with a flatter fruit (rain trees) became more common, leading to evolutionary change of smaller beaks in the bugs in that environment.

Question 20

What was the change?

Answer 20

Populations living where the rain tree is have shorter beaks as they are able to get more nutrition on average. This means they are more fit and have a greater number of offspring. They are favoured in this environment. NATURAL SELECTION.

Question 21

Evidence for Tree of Life and Descent with Modification?

Answer 21

• Homology
• Biogeography
• Fossil Record
• These serve the purpose of introducing observations about the world or things in it that have an immediate and ready explanation under the TOL for the pattern of evolution and don’t fit very well under other models/explanations.

Question 22

What is Homology?

Answer 22

“Similarity resulting from common ancestry”

• Observing features you see in two similar species: the explanation for seeing it is because they’re inherited from a common ancestor.
• Different versions of the same thing or character historically

Question 23

How does homology make sense?

Answer 23

It makes sense under the Tree of Life. Having widespread homology supports a tree of life idea.

Question 24

What does it mean?

Answer 24

2 similar species who have similar or shared traits may have inherited them from a common ancestor?

Question 25

Examples of homology?

Answer 25

- "Standard" anatomical homologies - Vestigal structures - Molecular homologies

Question 26

Examples of "standard" anatomical homologies?

Answer 26

Many mammals have a similar form (arm, fin, wing, leg in different animals) despite having different functions. - They are homologs of the same common ancestor. - Similar features stem from having the same common ancestor

Question 27

What are vestigial structures?

Answer 27

They are structures with little or no function, derived from more complex structures. - They come from a recent common ancestor who would have had the functional version.

Question 28

Example of vestigial structure?

Answer 28

Remnant hind-limb bones in whales and some snakes.

Question 29

Functional structure in non-functional forms means?

Answer 29

Vestigial structures: a different version of the same homologs. Function was lost along the way from ancestor but a small nonfunctional form is transferred.

Question 30

Molecular Homologies?

Answer 30

Homologies at the biochemical level

Question 31

Example of molecular homologies?

Answer 31

The universal genetic code is shared by the vast majority of animals & plants & protists & Bacteria & Archaea - We ALL have the same code

Question 32

What are pseudogenes?

Answer 32

They are molecular vestigial features: One organism contains a code for an amino acid that is 95% similar to the functional version, but it does not encode for the right protein. Another similar species has the functional protein.

Question 33

What can we determine with pseudogenes?

Answer 33

If we went back to the ancestors between those two organisms, it probably had a common ancestor with the functional protein.

Question 34

Homologies and the Tree of Life?

Answer 34

Often, nested distributions amongst organisms, following classification based on other similarities fits a tree of life model. - In other words, we expect to see a tree of life that fits our nested distribution of homologies.

Question 35

What do we see when we look at many homologies at once?

Answer 35

When we look at many different homologies, we see a dominant pattern. That is not to say that it is absolute, but that it is the more common pattern.

Question 36

Analogous structures?

Answer 36

Species with similar functions, but no common underlying structure (similarity is not from common ancestry) - We can see this on the tree of life as well

Question 37

What causes analogous structures?

Answer 37

The outcome of Convergent Evolution is having analogous structures.

Question 38

What do we see from analogous structures?

Answer 38

We might think that they have a common ancestor, but: - this is unlikely, as the underlying structure is not similar - therefore, there is no common ancestor between them

Question 39

What would the analogous structures look like on the tree of life?

Answer 39

A case where the tree of life had two branches that evolved very similarly, but do not come from the same branch on the tree. These two species would be analogous, but not actually closely related.

Question 40

Example of analogous structures (wings)?

Answer 40

- A moth and a hawk. Both have wings and are capable of flight, yet they have different types of wings. This means that they are not closely related.

Question 41

Example of analogous structures (flying squirrels)?

Answer 41

The North American flying squirrel and the Australian sugar glider both have a similar composition for their flight mechanism, yet they are very dissimilar in many other ways. - They are both much more similar to other organisms in their respective areas. - Therefore they are not very closely related, and more likely convergent evolution occurred in different branches of the tree.

Question 42

What is biogeography?

Answer 42

The geographic distribution of organisms - Some taxa (groups of similar species) are restricted to certain locations where they are endemic - Explanation: Descent from a common ancestor that lived in that location

Question 43

Example of biogeography?

Answer 43

Macropodiformes: There are many different species of kangaroos in Australia and New Guinea. They are distributed over the area and not found elsewhere.

Question 44

Another example?

Answer 44

There are many different, very similar plants in Hawai'i that occur naturally. They are all related and seen on all the different islands.

Question 45

The fossil record?

Answer 45

Descent with modification predicts ‘transitional forms' and the order of appearances by the fossil record.

Question 46

Advantage of the fossil record?

Answer 46

It allows us to look more directly at the past.

Question 47

What are transitional forms?

Answer 47

Forms with different aspects of different, older forms.

Question 48

Examples of transitional forms?

Answer 48

Good examples: - Groups with major adaptations associated with an ‘unusual lifestyle’ For instance: – Whales (fully aquatic mammals) – Birds (powered flight)

Question 49

Transitional forms in evolutionary progression?

Answer 49

We should see relatives of species B with species A's features if they are related. This organism will be a transitional form.

Question 50

Whale transitional forms?

Answer 50

Older whales were more similar to land animals, progressing more as they began adapting to the fully aquatic lifestyle.

Question 51

Whale's adaptations to being permanently aquatic?

Answer 51

Adaptations to being permanently aquatic: * Lack hind-limbs * Forelimbs lack distinct fingers * Dorsal fin, caudal flukes * Nostrils on top of head,..... etc.

Question 52

Order of appearance?

Answer 52

When fossil record is good, ‘descendant’ groups should appear later in time than the earliest of their proposed ancestral groups.

Question 53

Example of the order of appearance?

Answer 53

Whale example: - First aquatic whale-like forms: ~50 million years ago - First (eutherian) land mammals: ~80 million years ago