SPECIATION AND MACROEVOLUTION

• Speciation


  The evolution of one or more species from a single ancestor species
• Speciation


  • Can occur when members of a population become isolated from each other
  • Is the process whereby new species are formed

  
• Allopatric speciation


  The type of speciation when a group of individuals diverges from their original species due to a geographical barrier

  
• Sympatric speciation


  Represents the extreme opposite of allopatric speciation by being wholly independent of geographical context. New species form well within the dispersal range of the ancestral species through divergent natural selection to adapt to alternative habitats

  
• Despite living in the same area, a population splits into separate gene pools due to various isolation mechanisms
• Reproductive isolation mechanisms


  • Temporal isolation
  • Behavioral isolation
  • Ecological isolation
• Postzygotic barriers


  • Hybrid inviability (offspring do not survive)
  • Hybrid sterility (offspring are sterile)
• Factors that lead to speciation

  • Natural selection
  • Sexual selection
  • Polyploidy
• Examples of sympatric speciation in nature

  • Wheat (polyploidy)
  • Cichlid fish in African lakes (divergent feeding strategies and mating preferences)
• Adaptive radiation


  The process when a single species diversifies rapidly into various forms, each suited to different ecological niches due to environmental changes, resulting in multiple new species
• Factors that influence adaptive radiation


  • Availability of resources
  • Changes in the environment
  • Competition
• Steps in the process of adaptive radiation

  1. Ancestral species

  2. Colonization

  3. Isolation

  4. Adaptation

  5. Speciation
• Convergent evolution


  The process whereby distantly related organisms independently evolve similar traits to adapt to similar necessities
• Convergent evolution is the opposite of divergent evolution, in which related species evolve different traits
• Macroevolution


  Evolution above the species level, involving taxonomic groups over time, in contrast with microevolution
• The study of macroevolution involves the fossil record and genetic code comparison to support large-scale evolutionary patterns
• Developmental genes


  The study of how genes control development, where changes in genes controlling development can have major effects on the morphology of the adult organism
• Distinct types of developmental changes that affect morphology


  • Module duplication and adaptation
  • Individualization
  • Heterochrony
  • Allometric growth
• Hox genes


  A series of genes that set the identity of segments of insect bodies from head to tail
• Mutations in developmental genes can cause major morphological changes, such as extra wings or legs in fruit flies