Lecture 23 - Evo-Devo

Question 1

Name Some Features that Developed in Animals Over Time:

Answer 1

• Gene expression
• Cell position
• Growth

Question 2

Define Homology:

Answer 2

Similarity of the structure, physiology, or development of different species of organisms based upon their descent from a common evolutionary ancestor.

Question 3

What are Some Limits to Natural Selection?

Answer 3

• Fitness trade-offs
• Limiting factors (food, water and shelter availability)
• Small population size or low recombination rate
• Constantly changing environments prevent perfect adaptations.

Question 4

Where Does Variation Come From?

Answer 4

Changes in development.

Question 5

How can Finely-Tuned Development be Changed without Disruption?

Answer 5

Modularity - development based on discrete and interacting modules (e.g. - dissociation; limbs and eyes grow independently)

Question 6

How Many Body Plans of Animals are There?

Answer 6

~35.

Question 7

Name Some Physical Constraints of Organisms:

Answer 7

Laws of diffusion, hydraulics and physical support (e.g. - no rotating wheels with blood supply nor no giant insects).

Question 8

Name Some Pleiotropic Constraints of Organisms:

Answer 8

Pleiotropy: A gene plays different roles in different cells.

• Hox genes linked to stem cell proliferation
• Changing number of vertebrae increases risk of cancer
• Only exceptions are sloths and manatees.

Question 9

Name Some Morphogenetic Constraints of Organisms:

Answer 9

• Organisms depart from normal development in limited number of ways (e.g. - cannot have short middle finger)
• Reaction-diffusion mechanism
• Morphogenetic construction rules (e.g. - logarithmic spiral)

Question 10

How is Size Controlled in Repeated Structures?

Answer 10

• Via inhibitory cascade

- For example, teeth, fingers, vertebrae, body segments.

Question 11

How is Shape Controlled During Growth?

Answer 11

• Via power cascade

- For example, teeth, horns, claws.

Question 12

How are Molar Proportions Changed During Development?

Answer 12

Molars are initiated one at a time during development through the process of inhibition and activation to change their molar proportions.

Question 13

How Many Fossil Hominins Exist?

Answer 13

15 species.

Question 14

What is the Difference Between Function vs Development?

Answer 14

• Function explains change in size and proportions (e.g. - decreased bite force).
• Function cannot account for inhibitory cascade patterning at different sizes.
• Function leads to general result, but development explains how it was achieved.

Question 15

How is the Serial Structure in Vertebrates Identified?

Answer 15

• Through the 1/3 rule.

- Followed by limb segments, vertebrae and fingers.

Question 16

Explain the Development of Trilobites:

Answer 16

• Segments of pygidium and thorax follow inhibitory cascade in adults of trilobites.
• Segments follow inhibitory cascade during development as well.
• Pygidium segments are linear for 51 out of 53 species.
• Thorax segments are linear for 69 out of 99 species.

Question 17

Explain the Ontogeny of Trilobites:

Answer 17

1. Thoracic segments are linear early in development and remain linear
2. Thoracic segments can change pattern later in development.

Question 18

Do Modern Arthropods Have Similar Patterns to Their Ancestors?

Answer 18

Yes. Inhibitory cascade pattern occurs in early development however there is some deviation in adults.

Question 19

How Does Tooth Growth Occur?

Answer 19

• Tooth develops from tip to base, and expands laterally.

- Can measure rate of lateral expansion as length increases.

Question 20

Give Examples of Mammals:

Answer 20

Carnivores, deer, elephants, primates (including humans), whales, bats, pigs and marsupials.

Question 21

Name All Vertebrates:

Answer 21

Bony fish, sharks, reptiles, birds, dinosaurs.

Question 22

What is the Formula for Tooth Growth in a Power Cascade?

Answer 22

Tooth Growth:
log(Radius) = Slope * log(Distance) + Intercept

Power Function:
Radius = Intercept * Distance^Slope

Question 23

What are Some Shape Variables of Teeth and Their Corresponding Aspect Ratios?

Answer 23

Slope : Pointiness:

• Slope = 1; Pointy
• Slope = 0.5; Blunt

Aspect Ratio : Length

• Aspect Ratio = 1; Short
• Aspect Ratio = 2; Long

Question 24

How Would You Estimate an Elephants Age?

Answer 24

Through measuring their radius (or circumference) of their tusk.
- Longest tusk recorded: 3.5 metres.

Question 25

What are Some Ways to Predict Tusk Length?

Answer 25

The main way is to extrapolate linear patterns (via graphs) to juvenile tooth radius’. There are two forms of tusks: high or low slopes.

Question 26

Compare Horns vs Antlers:

Answer 26

Horns:

• Grow from tip to base
• Same direction as teeth

Antlers:

• Grow from base to tip
• Reverse growth direction still shows power cascade pattern

Question 27

Compare Juvenile vs Mature Thorns:

Answer 27

Juvenile:

• Pointed shape
• Follows power cascade

Mature Thorn:

• Concave shape
• Stretching of base causes deviation from power cascade

Question 28

What are the “Rules” to Evo-Devo?

Answer 28

• Discovery of new rules of development shows some limits placed on natural selection.
• May be considered “bias” rather than “constraint”
• Developmental rules often represent “default” patterns that can be altered.

Question 29

Evolutionary Developmental Biology Examines:

Answer 29

• How development affects evolution
• How evolution affects development
• How adaptation can be limited by developmental processes.

Question 30

Name a Morphological Construction Rule:

Answer 30

Power cascade.