bio lecture ch 22 (copy)

Key Concepts of Evolution

• Mutation

  • Introduces new variants to a population.

  • Alone, does not lead to evolutionary change without other forces.

• Evolutionary Forces

  • Genetic Drift

    • Random changes in allele frequencies within a population.

  • Migration (Gene Flow)

    • Movement of individuals between populations affecting genetic diversity.

  • Natural Selection

    • Three forms:

      • Directional Selection: Favors one extreme phenotype over others, causing a shift in a population's traits.

      • Stabilizing Selection: Favors intermediate variants, reducing variation and maintaining the status quo.

      • Disruptive Selection: Favors extremes over intermediate phenotypes, which may lead to speciation.

  • Non-random Mating (Sexual Selection)

    • Involves mate choice between sexes, which can shape population dynamics.

    • Two types:

      • Intrasexual Selection: Competition among individuals of the same sex.

      • Intersexual Selection: Mate choice based on preferred traits, often seen in females.

Mechanisms of Speciation

• Speciation

  • Process leading to the formation of new species through evolutionary forces creating sufficient differences.

  • Morphological Species Concept: Based on physical characteristics; used by paleontologists when reproductive behavior isn't observable.

Importance of Examples and Case Studies

• Zebra Finch Study:

  • Example of intersexual selection; female preference for males with red leg bands illustrates mate choice dynamics.

• Seahorses and Pipefish:

  • Unique reproductive roles where males are choosy, flipping traditional sex roles.

• Ring Species:

  • Phenomena illustrating gradual changes across populations in a circular geographic pattern where adjacent populations can interbreed but extremes cannot.

Challenges in Defining Species

• Conceptual Issues

  • Different species definitions may arise; biologists may disagree on classifications due to ecological isolation, behavior, or genetic testing.

• Bacterial Speciation:

  • Asexual reproduction complicates traditional definitions since individual organisms don't interbreed.

Introduced Ideas of Gradients and Clines

• Clines

  • Gradients of traits shown across different populations; driven by selection, drift, and gene flow.

  • Example: House sparrows display variation in body size and coloration based on environmental factors.

Reproductive Isolation Mechanisms

• Prezygotic Isolation

  • Mechanisms preventing mating or fertilization:

    • Behavioral isolation: Differences in courtship behaviors.

    • Temporal isolation: Mating at different times.

    • Mechanical isolation: Physical differences preventing mating.

• Postzygotic Isolation

  • Happens after fertilization; includes hybrid inviability or sterility.

Summary and Class Activities

• Students grouped to discuss various scenarios involving evolutionary concepts.

• Emphasis on collaborative learning and preparedness to discuss natural selection, mating choices, and speciation mechanisms in detail.

• Importance of the Endangered Species Act for biodiversity conservation.