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

• National Science Foundation (NSF) summer research initiatives available for students: NSF 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.