Lecture Notes: Speciation and Isolation

Introduction

• Concept of desiring a "dogcat," referencing childhood curiosity and a cartoon.
• Explanation of species: Organisms that can interbreed and produce fertile offspring.
• Domesticated dogs and cats consist of different breeds but belong to the same species.
• Video focus: Species level and how different species can (or cannot) interbreed.

Hybrid Species Example

• Zonkey: A hybrid between a donkey and a zebra.
  • Rare and typically sterile.
  • Demonstrates interbreeding of different species leading to offspring that cannot reproduce.
  • Reflects the species rule concerning reproductive isolation.

Speciation

• Speciation involves new species development via reproductive isolation.
• Speciation Types:
  • Allopatric Speciation:
    • Occurs due to geographic barriers (e.g., rivers, mountains).
    • Populations are separated and evolve separately over time.
    • Mechanisms like natural selection and genetic drift contribute.
  • Sympatric Speciation:
    • Occurs in the same geographic area but involves different isolating factors.

Isolation Types in Speciation

Prezygotic Barriers

• Behavioral Isolation:
  • Differences in behaviors, such as mating songs, prevent interbreeding.
  • Example: Eastern and Western meadowlark species are isolated by song differences.
• Temporal Isolation:
  • Species breed at different times (seasons, years, or times of day).
• Habitat Isolation:
  • Preferences for different habitats within the same area prevent interbreeding.

Postzygotic Barriers

• Zygote Formation occurs but:
  • Offspring may not be fertile (e.g., the zonkey).
  • Offspring may be weak or unable to survive.
  • Genetic incompatibility can prevent development of a viable embryo.

Key Takeaways

1. Variety of isolation types can lead to speciation.
2. A species can be affected by multiple types of isolation.
3. Isolation separates gene pools, but changes over time in gene pools come from mechanisms like genetic drift or natural selection.

Mechanisms of Change Over Time

• Natural Selection:
  • Variability exists naturally in populations.
  • Genes resulting in high fitness increase in frequency over time.
  • Isolation allows mechanisms to act separately on populations.

Conclusion

• Importance of exploring beyond these examples for a deeper understanding of speciation.