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.