L7 - Evolution and Early Diversification

Question 1

Assessing descent… how do we compare phenotypic traits?

Answer 1

• Observation and measurement suffice
• Evaluate degrees of similarity and account for patterns of change in time to reconstruct relationships and lines of descent
• Fossil sequences test inferred patterns of change

Question 2

Problems with these techniques?

Answer 2

• Environmental influence on phenotypes
• Ontogenetic (development of an organism usually from the time of fertilization of the egg to adult) changes
• Identifying “derived traits”
• Insufficient data from living and fossil organisms to unambiguously trace changes in time
• Lack of universal traits

Question 3

What are the chances of finding a fossil?

Answer 3

• Chance of dying in one piece
• Chance of being fossilized
• Chance of remaining undisturbed
• Chance of being exposed
• Chance of being found
• Chance of being recognized

Question 4

Advantages of comparisons involving molecular traits?

Answer 4

• Nucleotide sequences provide a direct record of all information stored in the genome
• Issues like plasticity or environmental influences that affect phenotypic trait, don’t affect the genetic record
• If all of life came ultimately from one ancestor: potential for universal traits

Question 5

Difficulties of comparisons involving molecular traits?

Answer 5

• Difficulties in the use of sophisticated technology
• Inferring patterns of change in time not intuitive
• Back mutation at a site in the sequence is possible and COMPLICATES ANALYSIS
• Assuming constant molecular clock: if you’re trying to relate the number of differences to an amount of time that has passed, you are making assumptions that may not be true

Question 6

How do we reconstruct phylogeny (lines of descent)?

Answer 6

1. Acquire nucleotide sequence data
   - Different portions of the genome relate to periods of time
2. Align the mostly like pairings of those sequences sequences from different organisms
   - Allow for mismatches due to point mutations, insertions, and deletions
3. Reconstruct most likely lines of descent
   - Assess the minimal number of steps required to change from one sequence to another and use this as a measure of relatedness across all the organisms in the analysis

Question 7

Characteristics of Early Marine Plankton (single-cell)?

Answer 7

A diverse community of photosynthetic eukaryotes in marine waters.
- Why are there so many different physical structures of plankton? Which one is optimal?
- Interplay between abiotic-biotic and biotic-biotic
- Stochasticity: Depends on random chance
- Depends on your evolutionary history

Question 8

What are “Acritarchs”?

Answer 8

• A group of eukaryote fossils probably including algae, ciliates, dinoflagellates, radiolarians, foraminiferans
• Many acritarchs had tests (shells)
  
  • An example of increasing structural complexity
  • Also made for a better source of fossil material

Question 9

Why did diversity increase?

Answer 9

• Changing environmental conditions
• Changing biotic conditions
• Interactions between these changes resulting in higher diversity

Question 10

Processes involved in the increase of Eukaryote diversity?

Answer 10

• Increase in size of genome: more proteins, and enzymes coded for, more opportunities for mutations to arise
• Sexual reproduction: meiosis increases possible variation/mixing
• Increase in structural complexity: locomotion (transport), protection
• Ecological changes: great oxidation event, energy sources, physical/biological landscape, photosynthesis in shallow water.

Question 11

How do we get from a diverse community of unicellular eukaryotes to multicellular organisms? Why?

Answer 11

• Random chance?
• Colonial hypothesis
  
  • Dividing cells do not separate after division
  • Mutation in cell membranes or walls?
• Greater surface area for photosynthesis?

Question 12

How do colonial photosynthetic protists work?

Answer 12

• Protist: any eukaryotic organism that is not an animal, plant, or fungus
• Colonial protists and algae illustrate the intermediate stage of complexity
• Specialization of cells: colonial life allows evolution of separate functions for individual cells
  
  • Feeding, reproduction, locomotion…
  • Different metabolic pathways turned on and off

Question 13

What are Ediacaran Fossils?

Answer 13

• Cryptic soft-bodied organisms (570 MYA) found in Australia in 1946
• Late Precambrian era

Question 14

How to evaluate Ediacaran diversity?

Answer 14

• Variety of forms: “Vendian animals”
  
  • leaflike fronds, round pads, worms
• Some resemble jellyfish, sponges
• Most are unique and unlike known animals

Question 15

What does the Ediacran seascape look like ~ 570 MYA?

Answer 15

• Small shelly fossils in ocean sediments
• Soft parts not preserved - hard to tell if the soft Ediacarans were much less present at the time or if their fossils are just much less preserved
• No idea what organism constructed the shells
  
  • What are the costs/advantages of shells and hard body parts?
    
    • Energy costs with producing more different and unique traits
    • More specific conditions required to produce said traits (climate, resources (Ca needed for shells), location)
    • New opportunities for locomotion and protection

Question 16

What is the Burgess Shale Assemblage

Answer 16

• A fossil (mid-Cambrian) marine community ~ 515 Ma
  
  • Yoho National Park, BC found in 1909
• Fossils include ancestors of many modern groups (Arthropods, worms, jelly fish)
• Also many mystery organisms…
  
  • Failed lines of evolution: offspring were not well adapted or simply victims of chance

Question 17

What is the “Pikaia”?

Answer 17

• What is believed to be the predecessor of humans
  
  • Ancestor of chordates, and therefore the ancestor of vertebrates; mammals and humans

Question 18

What is the Cambrian Explosion ~ 570-540Ma?

Answer 18

• Rapid onset of diversification in the animal kingdom
• All modern animal body plans established

Question 19

How did the Cambrian explosion occur?

Answer 19

• Biological factors in the Cambrian explosion
• Interplay between different organisms
• Increase in genetic complexity?
  
  • Enough DNA to code for a much greater range of structural and metabolic proteins
• Increase in structural complexity?
  
  • More body parts for variation and selection to act on?
  • More structures that were adapted to multiple functions?
• Change in the environment?
• Change in ecological relationships?

Question 20

Explain the concept of “fitness landscape”.

Answer 20

• “Roughening” the landscape
• If organisms mutate a little bit: some will be better than others
  
  • High fitness = more likely to survive
  • Low fitness = less likely to survive
• The species that survive will end up in specific geographic locations and diversity will increase = roughening

Question 21

Examples of ecological processes

Answer 21

• Burrowing priapulid worms
  
  • Predators of small molluscs with spines
  • Swallowed prey all face the same way
  • Well developed feeding behaviour

Question 22

Predator-prey “arms race”

Answer 22

• Predator-prey start to change one another over evolutionary time
• However, this is not a result of “purposeful” responses to the other organism
• But rather, the result of random chance (EVOLUTION DOESN’T HAVE A GOAL)

Question 23

What is the purpose of evolution?

Answer 23

• none!!!
• Variations arise through chance mutations
• Some mutations are positive, some negative, many neutral
• Selection, not the organisms, decides which variations will survive/success
• Always interpret evolution in terms of chance variations, selection, probabilities of survival and not, purpose and progress towards an objective

Question 24

What is co-evolution?

Answer 24

Selection of favourable mutations in a biotic interaction between different organisms

Question 25

How do predator-prey interactions increase diversity?

Answer 25

Many possible variations at each step in the process

Question 26

What were the physical factors that occurred in the Cambrian explosion?

Answer 26

- Much new diversity was apparently in shallow water marine environments - Increase in number and complexity of those habitats - Increase in availability of nutrients for metabolism and growth - Change in chemistry of environment

Question 27

Other considerable mechanisms for explosion?

Answer 27

- Heating and melting, ending of most recent "Snowball Earth" - With melting, new elements become available and have complex changes and interactions - Tectonic activity - CO2 degassing rate - Increased photosynthesis - Increased pO2 by 50-75% during Ediacaran period/beginning of Cambrian - Enough to support energy requirements for larger predators