BSC2010-evolution-8-2024

Macroevolution: Overview

  • Origin of species is a key concept in macroevolution.

  • Focus on the roles of leaves, buds, fruits, seeds, insects, grubs, and tool-using finches in species development.

Summer Research Opportunities

Microevolution vs Macroevolution

Microevolution

  • Changes in genotype frequencies within a population.

Macroevolution

  • Formation of new species through evolutionary processes.

Understanding Species

Definition

  • A species is defined as a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. (Ernst Mayr, 1942, Biological Species Concept)

Biological Species Concept: Limitations

  • Inapplicable to asexual organisms.

  • Cannot be applied to fossils.

  • The definition of "potentially interbreeding" is often unclear, especially with hybrids.

Reproductive Barriers

Types

  • Prezygotic Barriers: Prevent fertilization.

  • Postzygotic Barriers: Operate after fertilization.

Prezygotic Barriers

  • Habitat Isolation: Species occupy different habitats.

  • Temporal Isolation: Species breed at different times.

  • Behavioral Isolation: Different mating behaviors.

  • Mechanical Isolation: Anatomical differences prevent mating.

  • Gametic Isolation: Sperm and egg compatibility issues.

Postzygotic Barriers

  • Reduced Hybrid Survivorship: Hybrids have reduced survival rates.

  • Reduced Hybrid Fertility: Hybrids may be infertile.

Hybridization Examples

  • Pizzly Bear: Shows hybrid vigor in species with a history of separation.

  • European and American sycamores can interbreed despite long separation.

Speciation Processes

Allopatric Speciation

  • Definition: Speciation that occurs when geographic barriers separate populations.

    • Geographic barrier divides populations.

    • Gene flow is cut off leading to microevolution.

    • Examples: Hawaiian Drosophila and Antelope squirrels.

Sympatric Speciation

  • Definition: Species arise while sharing the same habitat, often found in plants.

    • Common forms are polyploidy and behavioral change.

Polyploidy in Plants

  • Mistakes during cell division lead to viable but genetically isolated organisms.

  • Types include:

    • Autopolyploidy: Chromosome duplication in a single species.

    • Allopolyploidy: Combining chromosomes from two different species.

Behavioral Change in Animals

  • Young return to new places to mate, leading to separate gene pools.

  • Example: Apple Maggot Fly.

Adaptive Radiation

  • Rapid evolution of diverse species from a common ancestor in response to new environmental conditions.

  • Notable instance: Hawaiian silverswords.

Coevolution

  • Mutual evolutionary influence between species within the same ecosystem.

  • Illustrated by the "Red Queen Hypothesis," suggesting co-evolving species must continuously adapt to each other.