Speciation

• Species


  Includes all the members of a population that can interbreed under natural conditions
• Reproductive isolation


  Any biological factor that prevents two populations from interbreeding when living in the same region
• Speciation


  The process by which new species arise
• Modes of Speciation


  • Reproductive Isolation
  • Geographic Barriers lead to Allopatric Speciation
  • Sympatric speciation
• Reproductive Isolation


  • Prezygotic mechanisms can occur due to physical barriers (ecological isolation, mechanical isolation, gametic isolation) or behavioural barriers (temporal isolation, behavioural isolation)
  • Postzygotic mechanisms prevents a fertilized egg from growing into a viable and reproducing adult
• Allopatric Speciation


  The evolution of populations into separate species as a result of geographical isolation
• Prezygotic Mechanisms


  Reproductive isolating mechanism that prevents interspecies mating and fertilization
• Postzygotic Mechanisms


  Reproductive isolating mechanism that prevents maturation and reproduction in offspring from interspecies reproduction
• Behavioural Isolation


  • Male frogs of different species have unique calls that attract only females of their own species
• Temporal Isolation


  • Pussy willows produce flowers in the early spring, reproductively isolated from plant species that produces flowers at a different time of year
• Ecological Isolation


  • The mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations and does not encounter the mountain species
• Mechanical Isolation


  • Male damselflies transfer sperm during an unusual mating flight, where the male and female genitalia of each species are uniquely shaped and physically incompatible with other species
• Gametic Isolation


  • Male gametes may not be able to recognize and fertilize an egg of a different species, such as in many marine animals where sperm recognizes eggs of their own species through chemical markers
• Zygotic mortality


  • Mating and fertilization are possible, but genetic differences result in a zygote that is unable to develop properly, such as in some species of sheep and goat
• Hybrid inviability


  • A hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity, such as when tigers and leopards are crossed
• Hybrid Infertility


  • Hybrid offspring remain health and viable but are sterile, such as mules which are sterile hybrid offspring of a horse-donkey cross
• Sympatric speciation


  The evolution of populations within the same geographic area into separate species