Large group of eukaryotes, exclusively soft-bodied
Why did the burgess shale group evolve from the ediacarion biota?
They are organisms with large spikes covering bodies for protection predators
Why did tiktaalik evolve from burgess shale group?
Front appendages (better for land) for pushing, upward facing eyes (alligator)
Extinction
The loss of all individuals of a species
Background extinction rate
Happens constantly
What is the background extinction rate?
A) ~ 3 families/million yr.
Mass extinction
A rapid decline in a large number of species, much higher than background extinction rate
5 mass extinctions so far
Which of the following best describes changes in diversity following mass extinctions?
C) Mass extinctions are followed by periods of rapid increased in diversity
There is adapted radiation. Species fill the niches that used to be filled
How do you test if we are in the 6th mass extinction?
Look at background extinction rates and current extinction rates
Estimated background extinction rate
2 extinctions/10,000 species/100 years
Every 100 years, 2 of every 10,000 species are expected to go extinct
This estimate higher than any background rate previously used to compare with modern extinction rates
Why is the very high estimated background extinction rate a good thing?
If background extinction rate estimate is too low, modern extinction rates may seem much higher just because background rate was so low
This would incorrectly indicate a 6th mass extinction
What determines modern extinction rates?
International Union for the Conservation of Nature
How are species classified?
Extinct (none remaining)
Extinct in the wild (exist only in captivity)
Presumed extinct (very likely extinct, but not confirmed)
2 estimates of modern extinction rate:
High conservative estimate
Conservative estimate
Highly conservative estimate
Includes only species classified as extinct
Conservative estimate
Includes species classified as extinct, extinct in the wild, and presumed extinct
Which do you think is a better estimate of species persistence and why?
Conservative, better reflects what happens in nature
Highly conservative>background then we are in another mass extinction
Are we in a 6th mass extinction?
Yes
Prokaryotes
Organisms with cells that lack membrane-bound organelles and a membrane-bound nucleus
Include domains Bacteria and Archaea
Eukaryotes
Organisms with cells that have membrane-bound organelles and a membrane-bound nucleus (domain Eukarya)
Include protists, plants, fungi, and animals
Prokaryotic genetic information
Have smaller genomes than eukaryotes
Chromosomes are circular rather than linear
Have plasmids: small, independently replicating, circular DNA molecules -> often carry alleles for antibiotic resistance
Ribosomes are small for gene translation
How do prokaryotic cells reproduce?
Binary fission: splitting one cell into two after replicating genetic information
Pathogenic bacteria
Bacteria associated with disease
MRSA, Lyme disease, cholera, etc
Antibiotic
"against life"
Kill pathogenic and beneficial bacteria
Can result in irritable bowel syndrome and secondary infections
How do we kill bacterial cells without killing our own cells?
Prevent cell walls from forming
Disrupt ribosomes that make protein needed for life
Beneficial bacteria
Gut flora: allow proper digestion of food and protect your bowels from pathogenic bacteria (~1-3% of of your body weight is bacteria)
Which best describes the relationship between humans and gut floral species?
C) Mutualism
Clostriduim difficile infections
Beneficial bacteria no longer check growth of C. difficile, results in severe diarrhea
Treatment for gut flora loss?
Fecal transplants
WHich of the following best describes the interaction between C. difficile and beneficial gut bacterial species?
D) Competition
Limitation on a shared resource
Archaea
Single celled prokaryotes
Often extremophiles: "lovers" of extreme conditions
Extreme thermophiles
Thrive in extreme heat (e.g. hot springs of Yellowstone)
Extreme halophiles
Live in extremely salty environments (e.g. the Dead Sea in Israel
Which is the best hypothesis for the relationship among bacteria, archaea, and eukarya?
C)
Eukaryotes
Organisms with cells that have a membrane-bound nucleus and organelles
Most are protists
Similarities between mitochondria and chloroplasts?
Both have their own lipid bilayers
Both have circular DNA molecules that can replicate independently
Both have their own ribosomes that are smaller than the ribosomes of the cell in which they live
Both reproduce by a splitting process similar to fission
Endysymbiont theory
Mitochondria and chloroplasts derived from ancestral prokaryotes that were engulfed by another cell -> relationship became symbiotic
Protists
A group of mostly unicellular eukaryotic organisms that are not fungi, plants, or animals
Are protists a valid evolutionary group?
No. Not a monophyletic group
Some protists are more closely related to plants, animals, or fungi
We still don't know how protists should be classified
What is the vast majority of the diversity of life?
Unicellular
Brown algae
Large, multicellular photosynthetic algae
Carotenoids
Orange-ish brown photosynthetic pigment
Contained in plasmids of kelp cells (plastids=broader group that includes chloroplasts)
Adaptations for aquatic life and photosynthesis
Holdfast
Blade
Stipe
Holdfast
Anchors to seafloor
Blade
Leaf-like structures increase photosynthetic surface areas
Stipe
Stalk-like structure brings blade closer to the ocean surface and therefore light
Holdfast, blade, and stipe are very similar to root, stalk, and leaf, but DNA analysis shows that they came from different evolutionary lineages. What kind of evolution is this?
Convergent evolution
What type of evolutionary group is green algae?
Paraphyletic group
Green algae are photosynthetic protists
Green algae=protists=closest relatives of land plants
Green Algae
Charophytes=closest relative of land plants
How are green algae related to environmental pressures of life on land?
Often live in intertidal zones: sometimes submerged, sometimes not
Zygotes coated with sporopollenin: tough polymer that prevents desiccation
Flagellated gametes: gametes "swim" to each other through water
No internal structural support -> supported by water
Challenges for movement onto land?
Must be able to avoid desiccation
Must develop supportive tissue to remain upright (and compete for sunlight)
Need to have gametes that don't require water to swim in to meet each other and achieve fertilization