L7 - Evolution and Early Diversification Flashcards
1
Q
Assessing descent… how do we compare phenotypic traits?
A
- 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
2
Q
Problems with these techniques?
A
- 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
3
Q
What are the chances of finding a fossil?
A
- 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
4
Q
Advantages of comparisons involving molecular traits?
A
- 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
5
Q
Difficulties of comparisons involving molecular traits?
A
- 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
6
Q
How do we reconstruct phylogeny (lines of descent)?
A
- Acquire nucleotide sequence data
- Different portions of the genome relate to periods of time - Align the mostly like pairings of those sequences sequences from different organisms
- Allow for mismatches due to point mutations, insertions, and deletions - 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
7
Q
Characteristics of Early Marine Plankton (single-cell)?
A
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
8
Q
What are “Acritarchs”?
A
- 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
9
Q
Why did diversity increase?
A
- Changing environmental conditions
- Changing biotic conditions
- Interactions between these changes resulting in higher diversity
10
Q
Processes involved in the increase of Eukaryote diversity?
A
- 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.
11
Q
How do we get from a diverse community of unicellular eukaryotes to multicellular organisms? Why?
A
- Random chance?
- Colonial hypothesis
- Dividing cells do not separate after division
- Mutation in cell membranes or walls?
- Greater surface area for photosynthesis?
12
Q
How do colonial photosynthetic protists work?
A
- 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
13
Q
What are Ediacaran Fossils?
A
- Cryptic soft-bodied organisms (570 MYA) found in Australia in 1946
- Late Precambrian era
14
Q
How to evaluate Ediacaran diversity?
A
- Variety of forms: “Vendian animals”
- leaflike fronds, round pads, worms
- Some resemble jellyfish, sponges
- Most are unique and unlike known animals
15
Q
What does the Ediacran seascape look like ~ 570 MYA?
A
- 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
- What are the costs/advantages of shells and hard body parts?
16
Q
What is the Burgess Shale Assemblage
A
- 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
17
Q
What is the “Pikaia”?
A
- What is believed to be the predecessor of humans
- Ancestor of chordates, and therefore the ancestor of vertebrates; mammals and humans
18
Q
What is the Cambrian Explosion ~ 570-540Ma?
A
- Rapid onset of diversification in the animal kingdom
- All modern animal body plans established
19
Q
How did the Cambrian explosion occur?
A
- 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?
20
Q
Explain the concept of “fitness landscape”.
A
- “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
21
Q
Examples of ecological processes
A
- Burrowing priapulid worms
- Predators of small molluscs with spines
- Swallowed prey all face the same way
- Well developed feeding behaviour
22
Q
Predator-prey “arms race”
A
- 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)
23
Q
What is the purpose of evolution?
A
- 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
24
Q
What is co-evolution?
A
Selection of favourable mutations in a biotic interaction between different organisms
25
How do predator-prey interactions increase diversity?
Many possible variations at each step in the process
26
What were the physical factors that occurred in the Cambrian explosion?
- 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
27
Other considerable mechanisms for explosion?
- 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
