SS

BSC2010-evolution-9-2024

Introduction to Speciation and Extinction

  • Overview of biodiversity patterns in relation to geographical location.

  • High diversity found at the equator, with low diversity in other regions.

Convergent and Divergent Evolution

  • Convergent Evolution:

    • Different ancestors resulting in analogous structures.

    • Example: Wings found in insects, birds, and bats.

  • Divergent Evolution:

    • Different evolutionary paths from a common ancestor producing homologous structures.

    • Example: Pentadactyl limb structure in vertebrates.

Basic Elements of Speciation

  • Speciation requires:

    • A barrier to gene flow.

    • Genetic differentiation among populations.

    • Results in the emergence of daughter species.

Tempo of Speciation

  • Two Models:

    • Gradualistic Model: Slow and consistent divergence of isolated populations.

    • Punctuated Equilibrium: Long periods of stasis interrupted by rapid speciation events.

    • Examples from Earth’s history showcasing periods of slow evolution alongside rapid episodes.

Factors Affecting Speciation Rates

  • Key influences on speciation rates include:

    • Rates of mutation and natural selection.

    • Competition among species.

    • Availability of habitats and generation time.

    • Rates of environmental change.

Genetic Processes Leading to Speciation

  • Key Mechanisms:

    • Polyploidy: Changes in chromosome number that can lead to speciation.

    • Altered developmental processes that influence structure and function.

    • Mutations in Hox genes that control body plan development.

Heterochrony

  • Types of Heterochrony:

    • Sequence Heterochrony: Changes in the timing of development.

    • Allometric Heterochrony: Differences in the growth rate during development.

Examples of Heterochrony

  • Example: Axolotl showcasing neoteny (retaining juvenile features).

Extinction Rates

  • Extinction as a Constant Process:

    • Background extinction rates occur universally due to natural selection and randomness.

    • Mass extinction events lead to rapid species loss under specific conditions.

Historical Extinction Events

  • Permian Mass Extinction (250 million years ago): Estimated 83% of genera lost.

  • Cretaceous Mass Extinction (65 million years ago): Around 71% of species disappeared.

Mass Extinction Causes

  • Investigating causative events such as volcanoes, climatic changes, and meteor impacts.

  • Notable example includes the adaptive radiation of mammals following the Cretaceous extinction.

Tree of Life

  • Understanding the relationships among different life forms as influenced by speciation and extinction.

  • Includes various domains of life: Archobacteria, Protists, Fungi, Plants, Animals, and multiple evolutionary pathways leading to current biodiversity.