Speciation and Life History Notes

Geography of Speciation

• Allopatric Speciation:
  • Probably very common.
• Sympatric Speciation:
  • Probably rare (with exceptions).
• Parapatric Speciation:
  • Between Allopatric and Sympatric speciation.

Allopatric Speciation

• Lots of evidence supporting it, shown by the concurrence of geological and species histories.
  • Vicariance:
    • The Isthmus of Panama is an example.
  • Dispersal:
    • Illustrated by the example of "Aloha!"
• Ranges can change significantly over time.
• Current sympatry is NOT evidence of sympatric speciation, as it could be due to secondary contact.

Secondary Contact?

• Complete isolation (speciation):
  • Leads to full reproductive isolation and distinct species.
• Partial isolation:
  • May lead to:
    • Speciation fails, and the populations merge back together.
    • Hybrid zone formation (e.g., fire-belly toads).
    • Reinforcement of pre-zygotic isolation to prevent hybridization.

Sympatric Speciation

• Gene flow is a significant problem for sympatric speciation.
• Probably pretty rare overall.
• Can occur when a trait coincidentally causes both ecological and reproductive isolation, known as a “Speciation Trait.”
  • Example: Hawthorn/apple tree flies.
  • The timing of fruit production affects mating and host preference.
• Figure 9.22 illustrates sympatric speciation in apple-adapted flies (Rhagoletis pomonella) from a hawthorn-feeding ancestor.

Sympatric Speciation and Environmental Variation

• Islands are often too small for allopatric speciation to occur.
• Palms of Lord Howe Island demonstrate sympatric speciation.
• Soil type affects breeding behavior.
• Environmental variation contributes to speciation.
• Figures 9.27 A-D show the frequency of flowering in Kentia and Curly palms based on soil type.

Parapatric Speciation

• Gene flow is less problematic compared to sympatric speciation.
• Observed in Holbrookia maculata and Sceloporus undulatus where color affects reproduction based on the soil (Figure 9.28).

Chapter References

• Chapter 17: Earth and Life History.
• Chapter 21: Human Origin.

Chapter 17: History of Life

• Universe: Approximately 14 billion years since the Big Bang.
• Earth and solar system: Around 4.6 billion years old, with rock evidence dating back to 3.8 billion years ago.
• Earliest living things: Appeared about 3.5 billion years ago.
• Animals: Emerged approximately 800 million years ago.

Fossil Record

• Fossils:
  • Remains or traces of organisms that lived and died in the geologic past.
• Rock Types:
  • Igneous, sedimentary, and metamorphic rocks.
• Most fossils are found in sedimentary rock.
• Requirements for Fossilization:
  • Depositional (not eroding) environment.
  • Suitable conditions and hard parts of the organism.
  • No erosion since deposition.
  • Rock not subducted or metamorphosed.
  • Rock exposed on the surface.
  • Fossil found.

Plate Tectonics

• Key Features:
  • Volcanoes.
  • Subduction trenches.
  • Mid-oceanic ridges.
  • Oceanic and continental crust.
  • Lithosphere and asthenosphere.
  • Deep mantle.
  • Sinking plates.
• Convergence Types:
  • Oceanic-oceanic convergence forms trenches and island arcs.
  • Continental-continental convergence leads to mountain range formation.

Continental Drift

• Pangaea:
  • A supercontinent that existed approximately 225 million years ago (Mya).
• Laurasia and Gondwana:
  • Pangaea split into Laurasia (North America and Eurasia) and Gondwana (South America, Africa, Madagascar, India, Australia, and Antarctica) around 135 Mya.
• Land Mass Distribution Over Time:
  • Early Triassic (240 Mya):
    • Pangaea existed with mountainous highlands.
  • Late Jurassic (160 Mya):
    • Gondwana began to split.
  • Late Cretaceous (90 Mya):
    • Further separation of continents.
  • Oligocene (30 Mya):
    • Continents approaching their current positions.
• Pleistocene Glaciers:
  • Lowered sea levels, connecting terrestrial regions now separated by oceanic barriers.

Dating Methods

• Absolute Age:
  • Radiometric methods.
    • C-14 dating: Useful for materials less than 40,000 years old.
    • K-Ar dating: Applicable for materials older than 500,000 years.
    • Thermoluminescence (Thermo.) and Electron Spin Resonance (ESR): Used for dating between the ranges of C-14 and K-Ar.
• Process of Radiometric Dating:
  • Decay of parent atoms into daughter atoms over time.
  • The ratio of surviving parent atoms to accumulating daughter atoms indicates age.
• Relative Age:
  • Magnetic reversals at mid-ocean ridges.
  • Relative position of strata (layers of rock).
  • Comparison of fossils.

History of Life: General Patterns

• Climates, ocean and continent positions have changed, affecting organisms’ distributions.
• Continuous change in taxonomic composition.
• Mass extinctions have occurred.
• Rapid radiations of new species.
• Diversification in numbers and kinds of organisms.
• Replacement of extinct taxa with ecologically similar ones.
• Convergence on the current biota.