Systematics

• Speciation, the origin of new species, is at the focal point of Darwin's evolutionary theory
• Evolutionary theory must explain how new species originate and how populations evolve
• Microevolution


  Adaptations that evolve within a population, confined to one gene pool
• Macroevolution


  Evolutionary change above the species level
• In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth
• Biological Species Concept


  A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations
• Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms
• Gene flow between populations can be detected by analysing gene trees
• Reproductive isolation


  • Prezygotic barriers
  • Postzygotic barriers
• Prezygotic barriers


  Biological factors that impede two different species from producing viable, fertile offspring before fertilization
• Postzygotic barriers


  Biological factors that prevent the hybrid zygote from developing into a viable, fertile adult
• The biological species concept cannot be applied to fossils or asexual organisms
• Morphological species concept


  Defines a species by structural features
• Ecological species concept


  Views a species in terms of its ecological niche
• Phylogenetic species concept


  Defines a species as the smallest group of individuals on a phylogenetic tree
• Allopatric speciation


  Speciation that occurs when a geographic barrier separates populations
• Sympatric speciation


  Speciation that occurs without geographic separation
• Polyploidy is common in plants and can lead to sympatric speciation
• Sympatric speciation can also result from habitat differentiation and sexual selection
• Possible outcomes of hybrid zones over time

  • Reinforcement
  • Fusion
  • Stabilizing
• Punctuated equilibrium


  Periods of apparent stasis (no change) punctuated by brief periods of rapid change
• Gradualism


  Slow continuous change over time in a species' existence
• Genomics is enabling researchers to identify specific genes involved in some cases of speciation
• Macroevolution is the cumulative effect of many speciation and extinction events
• What you should now be able to do

  • Define and discuss the limitations of the four species concepts
  • Describe and provide examples of prezygotic and postzygotic reproductive barriers
  • Distinguish between and provide examples of allopatric and sympatric speciation
  • Explain how polyploidy can cause reproductive isolation
  • Define the term hybrid zone and describe three outcomes for hybrid zones over time
• Taxonomists use a system of classification that includes categories such as domain, kingdom, phylum, class, order, family, genus, and species.
• Evolutionary theory


  Must explain how new species originate and how populations evolve
• Types of evolution


  • Microevolution
  • Macroevolution
• Microevolution


  A type of evolution that consists of adaptations that evolve within a population, confined to one gene pool
• Macroevolution


  A type of evolution that refers to evolutionary change above the species level
• Reproductive isolation


  The Biological Species Concept emphasizes this
• Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms
• Species


  A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations (According to the biological species concept)
• Barriers to Interbreeding


  Reproductive Isolation
• Reproductive isolation


  The existence of biological factors (barriers) that impede two different species from producing viable, fertile offspring
• Hybrids


  The offspring of crosses between different species
• Prezygotic barriers block fertilization by


  • Impeding different species from attempting to mate
  • Preventing the successful completion of mating
  • Hindering fertilization if mating is successful
• Prezygotic barriers


  • Temporal
  • Habitat
  • Behavioral
  • Mechanical
  • Gamete Isolation
• Habitat isolation


  A type of pre zygotic barrier wherein two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
• Temporal isolation


  A type of pre zygotic barrier wherein species that breed at different times of the day, different seasons, or different years cannot mix their gametes