APS121 Evolution - Wellman Flashcards
Neo-Darwinian theory can be summarized in six propositions. What are they?
- Reproduction
- Excess
- Variation
- Selection
- Divergence
- Ancestry (all share 1 common ancestor)
What is taxonomy?
The science of classification of organisms
What is phylogeny?
The study of evolutionary relationships
How old is the earth?
4.6 billion years old
The fossil record is incomplete and highly biased. How is it incomplete?
- Very few organisms that ever live end up fossilised (even ewer collected and studied)
- Entire species or higher taxa may not be preserved. Perhaps due to low preservation potential, small population, small geographic area, short period of existence
How is the fossil record biased?
- Certain environments more likely to be preserved than others (net deposition over erosion - e.g. marine organisms more likely to be preserved)
- Organisms with more hard and readily preserved tissues are more likely to preserved (bone, tooth, shell, wood etc.)
Give some examples of environmental change through time
- Solar luminosity
- Distance between earth and moon (tides)
- Continental drift
- Changing atmosphere and climate change
- Milankovitch cycles (around sun)
- The evolving biota
- Rare events (Tsunamis, supereruptions, meteorite impacts, mass extinctions)
What is the order of taxonomic groups?
Kingdom Phylum Class Order Family Genus species
What is cladistics?
- The most widely used method of determining phylogeny nowadays
- Based on evolutionary relationships - classifies species according o how recently they share a common ancestor
- assumes life only evolved once and diversity originated through descent with modification
- reconstruct phylogeny through formal character analysis (only presence of homologous characters is used)
- illustrated using diagrams called cladograms
What are symplesiomorphies?
Shared ancestral characters
What are synapomorphies?
Shared derived characters - used to work out phylogenetic relationships
What are autapomorphies?
Characters unique to one species or group - used to define taxonomic groups
What are monophyletic groups?
Contain latest common ancestor plus ALL its descendants - used for cladistics
What are paraphyletic groups?
Not including all descendants of common ancestor (part of monophyletic group removed or missing) - meaningless for cladistics
What are polyphyletic groups?
Most recent common ancestor assigned to some other group and not the group itself - defined on the basis of convergence, or non-homologous characters assumed to have been absent in the latest common ancestor - meaningless for cladistics
What are the three domains?
Archaea, bacteria, eukarya
What are the five kingdoms?
Monera, Protista, Animalia, Fungi, Plantae
How big do prokaryotic cells tend to be as opposed to eukaryotic?
Prokaryotic: 1-10 micrometres
Eukaryotic: 10-100 micrometres
what are flagella made of in prokaryotes?
Flagellin
How do prokaryotes reproduce?
Binary fission - tend to be asexual but some parasexual
Where do the less numerous and diverse archaebacteria inhabit?
Extreme environments (e.g. thermophiles, halophiles)
How was the earth formed 4.6 billion years ago?
Gravitational accumulation of dust and larger objects. Mass melts and differentiates into core, mantle and crust (iron and nickel migrate to centre, silica and aluminium minerals form crust).
+ moon forms during major collision
What is the age of the oldest rocks on earth?
- 75 billion years old (when crust began to solidify)
- oceans and atmosphere partially begin to condense out
Why was the progress of the development of the Earth retarded >3.8 billion years ago?
Continuous bombardment of large objects - with released energy sufficient to boil of the oceans and atmosphere (along with any prebiotic components)
- active with plate tectonics and weathering and erosion
<3.8 billion years ago, when meteorite bombardment decreased in intensity, the planet cooled below a threshold that allowed oceans and atmosphere to condense out. What did this allow?
Organic compounds to begin to be synthesised and accumulate
When is the earliest fossil evidence for life on earth?
3.5 billion years ago
What is the panspermia theory?
Life (or its precursor) was delivered to earth by a comet from elsewhere in outer space
Why is it believed that prokaryotes originated before eukaryotes?
They appear earlier in the fossil record, they are simpler in virtually every aspect, and there is evidence that eukaryotes evolved from prokaryotes
What are the fundamental similarities between prokaryotes and eukaryotes?
The method of transmitting information in triplet code in DNA and translating it into proteins
All amino acids are laevo-rotatory and in nucleic acids all the sugars are dextro-rotatory
What is LUCA?
Last Universal Common Ancestor
What chemicals were produced by simulating conditions on primitive earth?
Amino acids, purines and pyramidines of RNA and DNA (although not thymine), sugars, porphyrins, complex tar-like substances.
What are some potential energy sources for the formation of life?
The sun, radioactivity, electric discharges (e.g. lightning), volcanic (e.g. hot springs and black smokers)
What came first DNA or proteins, given that proteins are the end product but are essential as enzymes in translating and copying the information in DNA? What was the dramatic breakthrough regarding this in the 1980s?
Self-splicing RNA was discovered - speculation on the origin of life began to centre on an “RNA world” - we have the basic chemicals, replication mechanism and energy sources
Initially, early RNA-based life would have survived using the chemicals comprising the “primordial soup”. When this ran out they would have to develop novel metabolic pathways, such as…
Chemoheterotrophism - C source and energy from consuming organic molecules
Chemoautotrophism - C source CO2, energy source from oxidising inorganic substances e.g. Fe2+
Photoautotrophism - C source CO2, energy from light
Photoheterotrophism - C source organic material, energy from light
Obligate anaerobes are…
Poisoned by oxygen and live exclusively by fermentation or anaerobic respiration where electrons are accepted by NO3- or SO4- rather than O2
Obligate aerobes…
Use oxygen for cellular respiration and cannot grow without it
Facultative aerobes…
use oxygen if it is present but can grow by fermentation in an anaerobic environment
What is the evidence of early prokaryotic life?
- Fossil stromatolites - mounds, columns, sheets of sedimentary rocks that were originally formed by the growth of layer upon layer of cyanobacteria (single-celled photosynthesising microbes) - mucus secreted by bacteria collects grains of sediment and they are stuck together with calcium carbonate (also from the bacteria).
- Fossil microorganisms - e.g. silicified in cherts, or resistant cell walls called acritarchs preserved in siltstone
- Carbonaceous matter that can be identified chemically as the product of ancient life (ratio of C12 to C13 altered due to rubisco as rubisco favours light carbon)
What do cyanobacteria produce as a bi-product of their metabolism that is useful for later life forms?
Oxygen
What is the evidence for the environment becoming aerobic?
Banded iron formations (BIFs), pyritic conglomerates, red beds
What were the early oxygen sinks of the aerobic environment?
- Volcanic gases that comprised the early atmosphere readily combine with oxygen as it is very reactive
- Dissolved iron that scavenged o2 to from BIFs
- Microorganisms carrying out aerobic respiration - earliest organisms were no doubt facultative, respiring aerobically when O2 was available, but switching back to anaerobic fermentation when oxygen was in short supply
Evolution has no…
foresight
What are the 2 main theories for the origin of the eukaryotic cell?
Symbiosis theory vs elaboration of the cell membrane
When were fossilised acritarchs large enough to suggest that they were eukaryotes?
2 billion years ago
Why is symbiosis theory supported the most?
Explains origin of:
Mitochondria - DNA more similar to that of facultative aerobes than other eukaryotes
Chloroplasts - DNA more similar to that of cyanobacteria
Flagella and cilia - resemble spirochaete bacteria (already found in symbiotic relationship with other bacteria)
Mitosis - spindle centrioles equivalent to tubules in cilia/flagella
When do acritarchs reach their zenith in terms of diversity and size?
950-850Ma
850-675Ma acritarchs suffer major wane with various extinction events
What is the evidence of a snowball/slushball earth which may have lead to a series of genetic bottleneck events?
Series of extensive glaciations extending into equatorial latitudes
In asexually reproducing organisms variation is due to…
mutation alone
In sexually reproducing organisms variation is due to…
mutation, independent assortment and crossing over
What is the problem with sex?
There is a 50:50 ratio of males to females - inefficient as 50% of the population are not reproducing at any one time - yet 98% of eukaryotes reproduce sexually
What are the advantages of sex?
Can combine advantageous mutations and lose deleterious mutations (as they are passed onto half the offspring, not all). and can achieve more variation than with asexual reproduction
What are the main theories as to why sex evolved?
- faster evolution and adaptation
- method of fending off diseases and parasites (more variation = more immunity)
- Method of repairing genes
- historical accident (“cop-out”)
Sex had probably evolved by…
1,200Ma
- some primitive eukaryotes do not reproduce sexually
When did multicellular life first evolve?
1000Ma
- but evolved several times independently in different biological groups
- probably evolved via experimentation with colony formation
What is the advantage of multicellular life?
Division of labour
Different cells can differentiate to make them optimal for different functions
What is a metazoan?
Multicellular animal
What characteristics do metazoans share?
- Multicellular body formed from different kinds of cells
- The ability to manufacture the protein collagen
- A reproductive cycle with gametes produced by meiosis
- A nervous system comprised of neurones (except in sponges)
What do molecular clock studies do?
Compare the same gene in 2 organisms and see how much they differ - if we know the rate at which mutations build up we can work out how long ago they diverged
What are evo-devo studies?
Molecular genetics of animal development - take genes and work out what they do and compare genes throughout phylogeny and work out where they arose
What 2 groups can animals be divided into?
Diploblasts (2 wall layers) and triploblasts (3 wall layers - endoderm, mesoderm, ectoderm)
When was the late precambrian period, when the ediacara biota are found?
630-542Ma
The first ediacara biota (frond ones and flat ones) had no mouth, gut or anus. How is it suggested they fed?
Using unicellular photosynthetic algae in quilt compartments, taking in substances through the body wall, or by chemosymbiosis where bacteria carried out metabolism.
What is the first evidence of organisms with a gut?
Trace fossils of triploblastic organisms - can only make trace if have a gut
What are found in the early cambrian fossils?
Small shelly fossils - shells were disarticulated elements of a skeletal covering that had yet to evolve into a large discrete shell covering the entire organism.
- but almost certainly an adaptation against predation, suggesting predators were present
- these organisms probably represent either an extinct phylum close to the molluscs or some form of annelid
What are found in the middle cambrian fossils?
Cambrian explosion - fossilised hard parts, including representatives of all modern phyla. some exceptionally preserved soft components as well - huge array of arthropods.
What is a key question to ask about the diversification of animals?
Did they diversify during ediacaran times with a slow fuse or explosively during the middle cambrian (i.e. does the cambrian explosion represent the appearance of fossilizable parts, meaning it is an artefact of the fossil record, or a true evolutionary burst to a large size and increased anatomical variety?
+ why have no new phyla appeared since the cambrian explosion
What caused the cambrian explosion?
- Environment - e.g. atmospheric O2 levels begin to rise dramatically at the precambrian/Cambrian boundary - may have triggered the evolution of large animals
- Ecology - eyes evolved separately on several occasions - predation creates evolutionary bottlenecks - predators evolved eyes and created an arms race - potentially eradicated ediacara, or they evolved burrowing and hiding
Contingency
Randomness - not popular these days
