Speciation Notes (VCE Biology Unit 4)

Speciation Overview

  • Speciation is the formation of new distinct species over the course of evolution.
  • It occurs when a barrier between populations leads to them undergoing natural selection separately.
  • A species is defined as organisms that can breed with one another and whose offspring can reproduce.

Genetic Changes in Populations

  • Allele frequencies change in a population's gene pool due to multiple factors:
    • Environmental selection pressures
    • Genetic drift
    • Gene flow
    • Mutations as the source of new alleles
  • Consequences of changing allele frequencies:
    • Increases or decreases in genetic diversity
  • Human influence on gene pools:
    • Manipulation through selective breeding programs
  • Pathogen dynamics and public health implications:
    • Bacterial resistance
    • Viral antigenic drift and shift
    • Ongoing challenges for treatment strategies and vaccination against pathogens

Changes in Species Over Time (Fossil Record and Speciation)

  • Changes in species through geological time are evidenced by the fossil record,
    • Faunal (fossil) succession
    • Index fossils and transitional fossils
    • Relative dating and absolute dating of fossils
  • Speciation as a consequence of isolation and genetic divergence:
    • Galapagos finches as an example of allopatric speciation
    • Howea palms on Lord Howe Island as an example of sympatric speciation

Determining the Relatedness of Species

  • Evidence of relatedness between species:
    • Structural morphology:
    • Homologous structures
    • Vestigial structures
    • Molecular homology:
    • DNA sequences
    • Amino acid sequences
  • The use and interpretation of phylogenetic trees as evidence for relatedness between species

Human Change Over Time

  • Shared characteristics that define mammal, primate, hominoid, and hominin groups
  • Major trends in hominin evolution from Australopithecus to Homo:
    • Changes in brain size
    • Changes in limb structure
  • The human fossil record as a classification scheme that remains open to interpretation, contested and refined with new evidence
    • Evidence for interbreeding between Homo sapiens and Homo neanderthalensis
    • Evidence of new putative Homo species
  • Use of fossil and DNA evidence (mtDNA and whole genomes) to explain the migration of modern human populations around the world
    • Migration patterns of Aboriginal and Torres Strait Islander populations and their connection to Country and Place

Daily Review (Page 4): Selective Breeding Practice

  • Identify an organism that has been selectively bred:
    • __
    • __
  • Outline the process of selective breeding:
    • __
    • __
  • Potential consequences of selective breeding:
    • __
    • __

Allopatric vs Sympatric Speciation (Learning Intentions and Success Criteria)

  • Allopatric speciation: geographic barrier separates populations, leading to independent evolution
  • Sympatric speciation: speciation occurs in the same geographic area
  • Learning goals:
    • I can explain allopatric speciation and give an example
    • I can explain sympatric speciation and give an example
    • I can list and explain various types of isolations

Key Terms

  • What is speciation?

    • Speciation is the formation of new distinct species over the course of evolution. It occurs when a barrier separates populations, causing them to undergo natural selection separately. A species is made up of organisms that can breed with one another and whose offspring can reproduce.

  • Inter-species relations

    • Sometimes organisms from two different species mate; however, their offspring have a lower survival rate and/or cannot produce viable offspring (they’re sterile).
    • Example: Zonkey — a zebra bred with a donkey; zonkeys are sterile, hence not a viable species cross.

  • Types of speciation

    • Speciation occurs when a barrier stops interbreeding. Over time, natural selection acts on both populations separately, leading to genetic differences.
    • Allopatric: a geographic barrier (e.g., river, mountain, road, fence) separates populations.
    • Sympatric: speciation occurs in the same area

  • Sympatric speciation (details)

    • Prezygotic isolation: barriers that prevent a zygote from forming
    • Behavioural isolation: different mating calls/songs within the same species
    • Temporal isolation: different breeding times (daily, seasonal)
    • Habitat isolation: different sub-habitats within the same area
    • Postzygotic isolation: barriers that prevent a zygote from developing or reproducing
    • Offspring are weak and may not survive long
    • Embryo cannot form due to genetic incompatibility
    • Offspring is sterile (cannot reproduce)

  • Example of allopatric speciation

    • Galapagos finches:
    • Finches dispersed from South America to the Galapagos
    • Isolated from mainland birds and between islands with varied habitats
    • Over time, different environments imposed different selection pressures, leading to distinct species (vegetarian, warbler, tree, ground finches)
    • After many years, different species could no longer mate to form viable offspring

  • Example of sympatric speciation

    • Howea palms on Lord Howe Island: two sister species (Howea forsteriana and Howea belmoreana)
    • Initially described as a single species
    • Divergence linked to flowering times and soil types
    • Howea belmoreana prefers neutral to acidic soils
    • Howea forsteriana prefers soils rich in calcarenite with a more basic pH
    • This ecological difference can lead to reproductive isolation within the same island

Connections to Foundational Principles and Real-World Relevance

  • Speciation integrates core evolutionary concepts: mutation, selection, drift, gene flow, and isolation
  • Fossil evidence (dating methods) provides a chronological framework for diversification and biogeography
  • Phylogenetics and molecular data (DNA, mtDNA, whole genomes) illuminate lineage relationships and migration patterns
  • Human evolution highlights the complexity of interpretation in science and the impact of new evidence on hypotheses
  • Interbreeding events between Homo sapiens and other hominins shape our understanding of human ancestry
  • Migration and population history of Indigenous populations emphasize the link between biology, culture, and place

Notes on Ethical, Philosophical, and Practical Implications

  • How interpretation of the fossil record can change with new evidence reflects scientific humility and the evolving nature of knowledge
  • Interbreeding evidence challenges simple “tree of life” models and promotes more networked views of human evolution
  • Understanding the migration of populations intersects with cultural heritage, identity, and connection to land (e.g., Aboriginal and Torres Strait Islander populations)