Chap 22

• Speciation is the process by which one species splits into two or more species.
• Speciation forms a conceptual bridge between microevolution and macroevolution
• Microevolution consists of changes in allele frequency in a population over time
• Macroevolution refers to broad patterns of evolutionary change above the species level
• The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.
• Reproductive isolation is the existence of biological barriers that impede two species from producing viable, fertile offspring
• Hybrids are the offspring of crosses between different species
• Prezygotic barriers block fertilization from occurring by Impeding different species from attempting to mate, preventing the successful completion of mating and hindering fertilization if mating is successful
• Habitat isolation is when two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
• Temporal isolation is when species that breed at different times of the day, different seasons, or different years cannot mix their gametes
• Allochrony - species using the same area or resource, but at different times (includes different mating seasons)
• Behavioral isolation is when Courtship rituals and other behaviors unique to a species are effective barriers
• Mechanical isolation is when morphological differences prevent successful mating
• Gametic isolation is when sperm of one species may not be able to fertilize eggs of another species
• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult by Reduced hybrid viability, Reduced hybrid fertility and Hybrid breakdown.
• Reduced hybrid viability is when Genes of the different parent species may interact and impair the hybrid’ s development or survival
• Reduced hybrid fertility is when even if hybrids are vigorous, they may be sterile.
• Hybrid breakdown is when some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile.
• The morphological species concept defines a species by structural features.
• The ecological species concept views a species in terms of its ecological niche
• The phylogenetic species concept defines a species as the smallest group of individuals on a phylogenetic tree
• Speciation can occur in two ways

  Allopatric speciation (Different “country”) (geographic isolated)

  Sympatric speciation (Same “country”)(no geographic isolation)
• Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division. (sympatric speciation)
• An autopolyploid is an individual with more than two chromosome sets, derived from one species. (sympatric speciation)
• An allopolyploid is a species with multiple sets of chromosomes derived from different species (cannot interbreed with either parent species) (sympatric speciation)
• A hybrid zone is a region in which members of different species mate and produce hybrids
• Reinforcement occurs when hybrids are less fit than the parent species
• Fusion of the parent species into a single species may occur if hybrids are as fit as parents, allowing substantial gene flow between species
• Stability of the hybrid zone may be achieved if extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
• Macroevolution is the cumulative effect of many speciation and extinction events
• Patterns in the Fossil Record

  • The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear
  • These periods of apparent stasis punctuated by sudden change are called punctuated equilibria
  • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence
• In allopatric speciation, geographic isolation restricts gene flow between populations ; Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
• In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species 'Sympatric speciation can result from polyploidy, natural selection, or sexual selection
• In allopatric speciation, gene flow is interrupted when a population is divided into geographically isolated subpopulations
• Sympatric speciation can result from polyploidy, natural selection, or sexual selection
• In allopatric speciation, geographic isolation restricts gene flow between populations

  • Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
  • Even if contact is restored between populations, interbreeding is prevented by reproductive barrie
• Speciation Rates

  • These periods of apparent stasis punctuated by sudden change are called punctuated equilibria
  • The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence
  • Fossil records support existence of BOTH patterns - suggest that speciation can be rapid

  A) Punctuated Model

  B) Gradual Model

  
• Label

  A) Reinforcement

  B) Fusion

  C) Stability