EEB Undergraduate Research Symposium Notes

EEB Undergraduate Research Symposium

Event Details

• Event: EEB Undergraduate Research Symposium
• Date: Monday, April 28
• Time: 12:45-5:00 PM
• Location: Biology/Physics Building, Room 131
• Refreshments: Light refreshments provided
• Sponsors: College of Liberal Arts and Sciences, Department of Ecology and Evolutionary Biology

Bonus Activity

• Worth a maximum of 5 bonus points.
• Answer the following questions about a newly discovered species.
• The first letter of the species name must match the first letter of your first name.
  • Example: If your name is Ed, a species named Pizza ellipticum would be acceptable.

Questions

1. Provide a link to a scientific article describing a new species (discovered between 1975 and the present day).
2. Where is the species found?
   • Geographic location
   • Habitat
3. Why had this species avoided detection until now?
4. What species concept did the researchers use to determine that this was a new species?
   • The article may not explicitly state this.
   • Critically analyze the article and explain why researchers could claim it was a 'new' species rather than a member of a previously described species.

Course Announcements

• The lowest exam score will be dropped.
• Final grade calculation:
  • Based on the three highest exam scores (100 points each).
  • Participation activities (maximum 40 points).
  • Any additional bonus points earned.
• Details available on the course website.

Feathers and Flight

• Feathers evolved before flight.

Hypotheses for the Initial Evolution of Feathers

1. Sexual selection
2. Thermoregulation

• Reference: Fig. 18.16

Dinosaur Feather Color

• How was the color of Anchiornis huxleyi feathers determined?
• Electron microscopy of melanosome structure.
• Melanosome: “melanin-containing organelles that determine key aspects of color”.
• Reference: Li et al. 2010 Science.
• Iridescent dinosaur feathers.
• A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution.
• Diameter of melanosomes: $900-300$ nm, n = $0.193$, $0 = 0.117$
• Length of melanosomes: $1000-2000$ nm, n = $0.231$, n = $0.241$
• Image credit: Velizar Simeonovski, Field Museum

Evolution of Flight

• How did flight evolve?
• Competing hypotheses:
  • Ground up
  • Tree down
• The exact mechanism is still unknown.
• Current research focuses on juvenile birds.
• Reference: Norberg 1990, Vertebrate Flight

Turtle Evolution

• Transitional fossils clarify turtle evolution
• Turtles are amniotes like us.
• Many amniotes have a diagnostic rib development pattern (under the shoulder blades).
• Turtle shells are formed by rib development going over its shoulder blades.
• Odontochelys represents an intermediate form that explains turtle relationships with amniotes.
• Reference: Fig. 2.22

Origin of Mammals

• There is a well-documented set of fossils showing reptile-like mammals.
• These fossils allow for evolutionary reconstruction of important mammal-specific traits.
• Middle ear bones.
• Reference: Fig. 18.17

Jaw and Middle Ear

• Mammalian middle ear bones are homologous to jaw bones in relatives.
• These bones became reduced in size and specialized for hearing.
• Mammalian jaw evolved a different hinge structure to compensate for these bones being used for hearing.
• Reference: Fig. 18.18

Taxonomy and Fossils

• Remember back to species concepts.
• Which concept applies well to fossils?
• Morphological and Phylogenetic species concepts can handle fossil data.
• A major drawback of the Morphological Species Concept (MSC) is not knowing where to draw the line as to what constitutes a new species.

Extinction

• Way more species have gone extinct than are currently alive.
• A few intervals of time have a disproportionate amount of extinctions
• Mass extinctions.
• Reference: Fig. 18.25
• Mass extinctions removed many families.
• Reference: Fig. 18.26
• Background extinction includes all the extinctions that were happening outside of mass extinction events.
• Reference: Fig. 18.25
• Lineages vary in their extinction rates over time.
• Reference: Fig. 18.27

Causes of Mass Extinctions

• Depends on the extinction event.
• The Cretaceous-Paleogene (K-Pg) extinction is highly studied.
• How do we know the timing of this extinction?
• In-class activity.
• Reference: Fig. 18.26

Iridium and Extinction Timing

• Iridium is rare on Earth but common in space.
• As researchers dug further into the crust, they encountered increased concentrations of iridium.
• The inference is that this iridium spike came from space.
• Back-of-the-envelope calculations suggest that an asteroid the size of a mountain hit Earth.
• Reference: Fig. 18.29b

Geological Formation Changes

• Limestone layers are visible above and below a quarter coin.
• The quarter is placed in a strip of sediment made of clay.
• Limestone is formed from marine invertebrate shells.
• The asteroid impact killed these lineages; therefore, no limestone formed for some time.
• Reference: Fig. 18.29a

Asteroid Impact Site

• Areas in the Caribbean were found to be rich in minerals consistent with high and quick pressure.
• Magnetic abnormalities in the Yucatán peninsula provided a key clue.
• Surveys later showed that the impact left a crater 180 km wide near Chicxulub, Mexico.
• Reference: Fig. 18.31

Consequences of the Asteroid Impact

• The Yucatán area was enriched with CaSO4 (anhydrite).
• The asteroid strike launched huge deposits of anhydrite and water.
• $CaSO4 + H2O = acid rain$
• Sulfur and other particulates would also hang in the atmosphere, blocking sunlight.

Further Effects of the Asteroid Impact

• The asteroid impact caused earthquakes and affected volcanic activity, such as the Deccan Traps of India.
• These would have released gases that changed the climate.
• Interestingly, these seem to have erupted before the asteroid's impact.

Tsunami and Ecological Disruption

• The impact would have created a 4 km tall wave.
• All these features would have tremendously altered Earth.
• However, not all K-Pg extinctions happened at the same time.
• The drawn-out process may have had to do with:
  • Disrupted ecological interactions
  • Lack of nutrients
• Reference: Fig. 18.26

Other Mass Extinctions

• The Permian-Triassic (P-T) mass extinction is believed to be volcanic.
• It has been timed to 252 million years ago.
• It happened simultaneously on land and sea according to the fossil record.
• The Siberian traps increased atmospheric carbon and warming.
• O2 levels went down to 13%.
• Marine O2 and temperature were critically affected too.

Sixth Mass Extinction

• Are we currently undergoing a sixth mass extinction?
• How to determine?
• Describe what sort of data you would collect.
• It would be impractical to intensely monitor every single species on Earth for the next 30 years.
• So, you’ll need to be creative.

Humans' Effect on the Planet

• How to measure the sixth mass extinction?
• Satellite photography documenting our encroachment on natural lands.
• Detailed monitoring of species that face extinction threats.
• Based on these approaches:
  • 100 to 1000 times greater extinction rate than background.
  • Reference: Cowie et al., 2022 Biological Reviews issue with quantifying extinction.

Areas of Greatest Threat

• Birds are particularly threatened.
• Reference: Hawkins et al., 2007
• Vascular plants are highly threatened, especially in certain ecoregions.
• Reference: Kier et al., 2005
• Suitability and quality of underlying data.
• Reference: Kier et al., 2005