Lecture on Species and Speciation

Introduction to Species

• Concept of species: organisms that can interbreed and produce fertile offspring.
• Example: Variety of domesticated dog breeds are the same species; same for cat breeds.
• Focus on species level in taxonomy.

Hybrid Offspring

• Different species can sometimes breed and have offspring.
• Example: Zonkey (hybrid of donkey and zebra) is typically sterile, fitting the species rule.

Speciation

• Definition: Development of a new species through reproductive isolation.
• Mechanisms like natural selection and genetic drift can lead to new species.

Types of Speciation

1. Allopatric Speciation

• Occurs due to geographic barriers (e.g., rivers, mountains) separating populations.
• Leads to genetic differences over time; populations may not interbreed even if reunited.

2. Sympatric Speciation

• Occurs in the same geographic area but other isolating factors are present.
• Without geographic separation, various barriers can still cause speciation.

Prezygotic Barriers

• Behavioral Isolation: Different behaviors prevent interbreeding (e.g., bird songs).
  • Example: Eastern and Western Meadowlark birds have different mating songs.
• Temporal Isolation: Different breeding seasons, years, or times of day.
• Habitat Isolation: Different preferred habitats within the same area.

Postzygotic Barriers

• Barriers after zygote formation prevent species from merging.
• Example: Zonkey's infertility.
• Issues with weak offspring or genetic incompatibility at embryonic stages.

Key Takeaways

• Isolation types discussed are only a subset; there are many more.
• Species can be affected by multiple isolation types.
• Isolation is not the mechanism for change over time; it separates gene pools.
• Mechanisms like natural selection affect separate gene pools leading to evolution.

Conclusion

• Encouragement to explore more isolation types leading to speciation.
• Reminder that change over time is due to mechanisms like genetic drift and natural selection.

Stay curious and continue exploring biology topics!