Origin of Species (Speciation)

• Speciation


  The formation of new species
• Evolutionary Theory


  It must explain how new species originates, or how populations evolve
• Types of Evolution


  • Microevolution
  • Macroevolution
• Microevolution


  • Adaptations that evolve within a population, confined to a single gene pool
  • Occurs over a short period of time
  • Does not result in speciation
  • Genetic information is being altered or rearranged
• Macroevolution


  • Evolutionary change above the species level
  • Occurs over a long period of time
  • Results in speciation
  • There is an addition or deletion in the genetic structure, which leads to the formation of new species
• Biological species concept


  Species is a group of populations whose members have the potential to interbreed, and produce viable, fertile offspring; they do not breed successfully with other populations
• Reproductive isolation


  The existence of biological factors or barriers that impede two different species from producing a viable offspring
• Pre-zygotic barriers


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


  Two species encounter each other rarely or not at all, because they occupy different habitats even though they are not isolated by physical barriers
• Temporal isolation


  Two species that breed at different times of the day, different seasons, or different years cannot mix their gametes
• Behavioral isolation


  The courtship or behavior that is unique to one species is an effective barrier
• Mechanical isolation


  The morphological difference of two different species can prevent successful mating
• Gametic isolation


  The sperm of one species may not be able to fertilize the egg of another species
• Post-zygotic barriers


  • Reduced hybrid viability (weak offspring)
  • Reduced hybrid fertility (sterile offspring)
  • Hybrid breakdown

  
• Reduced hybrid viability


  Successful fertilization, but results in a weak or frail offspring, which makes it prone to death
• Reduced hybrid fertility


  Species successfully made a healthy offspring, however the offspring is infertile — unable to produce one of its own
• Hybrid breakdown


  Offspring is produced and can reproduce, however the next generation is weak or sterile
• Other species concepts


  • Morphological species concept
  • Ecological species concept
  • Phylogenetic species concept
• Morphological species concept


  Defines species based on their morphological/structural features
• Ecological species concept


  Views species based on their ecological niche
• Phylogenetic species concept


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


  • Allopatric
  • Sympatric
  • Parapatric
  • Peripatric
• Allopatric speciation


  Occurs when species from the same population are separated by physical barriers (geographical/spacial isolation), like oceans, rivers, mountains, and deserts
• Sympatric speciation


  Occurs where organisms live in the same place but are reproductively isolated
• Peripatric speciation


  Occurs when a small group of a population breaks off from the larger group and forms a new species due to physical barriers
• Parapatric speciation


  Occurs when a species is spread out over a large area which results in mating restricted to a vicinity, even without physical barriers
• Hybrid zones


  Regions where members of different species mate and produce hybrids
• Possible outcomes in hybrid zones

  • Stability
  • Reinforcement
  • Fusion
• Broad patterns in speciation can be studied using the fossil record, morphological data, and molecular data
• Punctuated equilibrium


  Periods of apparently stasis or no change punctuated by periods of rapid change, contrasting with Darwinian gradualism