L7 - Evolution and Early Diversification Flashcards
Assessing descent… how do we compare phenotypic traits?
- 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
Problems with these techniques?
- 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
What are the chances of finding a fossil?
- 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
Advantages of comparisons involving molecular traits?
- 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
Difficulties of comparisons involving molecular traits?
- 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
How do we reconstruct phylogeny (lines of descent)?
- 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
Characteristics of Early Marine Plankton (single-cell)?
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
What are “Acritarchs”?
- 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
Why did diversity increase?
- Changing environmental conditions
- Changing biotic conditions
- Interactions between these changes resulting in higher diversity
Processes involved in the increase of Eukaryote diversity?
- 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.
How do we get from a diverse community of unicellular eukaryotes to multicellular organisms? Why?
- Random chance?
- Colonial hypothesis
- Dividing cells do not separate after division
- Mutation in cell membranes or walls?
- Greater surface area for photosynthesis?
How do colonial photosynthetic protists work?
- 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
What are Ediacaran Fossils?
- Cryptic soft-bodied organisms (570 MYA) found in Australia in 1946
- Late Precambrian era
How to evaluate Ediacaran diversity?
- Variety of forms: “Vendian animals”
- leaflike fronds, round pads, worms
- Some resemble jellyfish, sponges
- Most are unique and unlike known animals
What does the Ediacran seascape look like ~ 570 MYA?
- 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?
