Chapter 24: The Origin of Species

• speciation


  an evolutionary process in which one species splits into two or more species
• Speciation connects microevolution and macroevolution
• microevolution

  evolutionary change below the species level; including change in allele frequencies in a population over generations
• macroevolution


  evolutionary change above the species level; including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time
• Biological Species Concept


  definition of a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but not with other groups
• Biological species are defined by reproductive isolation
• reproductive isolation


  the existence of biological features (barriers) that impede members of 2 species from producing viable, fertile offspring
• Barriers prevent gene flow between two species & limit hybrids
• hybrid


  offspring resulting from the mating of individuals from two different species
• One barrier may not prevent all gene flow, but a combination can isolate a species
• prezygotic barrier


  (before the zygote) a reproductive barrier that impedes mating between species or hinders fertilization if the interspecific mating is attempted
• Prezygotic barriers act in 3 ways

  1. Impede members of different species from attempting to mate
  2. Prevent an attempted mating from being successful
  3. Hinder fertilization if mating is successful
• Types of Prezygotic Barriers

  • habitat isolation
  • temporal isolation
  • behavioral isolation
  • mechanical isolation
  • gametic isolation
• Which type of prezygotic barrier is described below?

  courtship rituals, pheromones, & songs that attract mates; such rituals enable mate recognition - a way to identify potential mates of the same species

  A) Behavioral

  
• Which type of prezygotic barrier is described below?

  species that occupy different habitats

  A) Habitat

  
• Which type of prezygotic barrier is described below?

  species that breed during different times of the day, different seasons, or different years cannot mix games

  A) Temporal

  
• Which type of prezygotic barrier is described below?

  mating is attempted, but morphological differences prevent its successful completion

  A) Mechanical

  
• Which type of prezygotic barrier is described below?

  sperm of one species may not be able to fertilize the eggs of another species

  A) Gametic

  
• postzygotic barrier


  (after the zygote) a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults
• What are the 3 types of postzygotic barriers?

  A) Reduced hybrid viability

  B) Reduced hybrid fertility

  C) Hybrid breakdown

  
• Which type of postzygotic barrier is described below?

  the genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment

  A) Reduced hybrid viability

  
• Which type of postzygotic barrier is described below?

  hybrids may be sterile because differences in chromosomes prevent normal gametes from forming

  A) Reduced hybrid fertility

  
• Which type of postzygotic barrier is described below?

  some first generation hybrids are viable & fertile, but when they mate w/ one another or either parent species offspring of the next generation are frail

  A) Hybrid breakdown

  
• Morphological Species Concept

  definition of species in terms of measurable anatomical criteria

  • can be applied to sexual & asexual organisms
  • relies on subjective criteria
• Ecological Species Concept


  definition of species in terms of ecological niche, the sum of how members of the species interact w/ the nonliving & living parts of the environment
• Phylogenetic Species Concept


  definition of species as the smallest group of individuals that share a common ancestor, forming one branch of the tree of life
• allopatric speciation


  the formation of new species in populations that are geographically isolated from one another

  
• Allopatric speciation can occur without changing geology
• In allopatric speciation, the separated gene pools can become different through:

  1. Mutations
  2. Natural selection
  3. Genetic drift
• sympatric speciation


  the formation of new species in populations that live in the same geographic area

  A) Sympatric

  
• Sympatric speciation is less common than allopatric speciation
• Sympatric speciation can occur due to:

  1. Polyploidy
  2. Habitat differentiation
  3. Sexual selection
• polyploidy


  a chromosomal alteration in which the organism possesses more than two complete chromosome sets; due to an accident in cell division
• autopolyploid


  an individual that has more than two chromosome sets that are all derived from a single species (ex: failure of cell division could double the number of chromosomes)

  A) autopolyploid

  
• allopolyploid


  a fertile individual that has more than two chromosome sets as a result of two different species interbreeding & combining their chromosomes

  A) allopolyploid

  
• Allopolyploids are fertile when mating with each other, but cannot interbreed with either parent species
• In allopatric speciation, new species form in geographic isolation which restricts gene flow.

  Different processes can produce genetic changes:

  1. Natural selection
  2. Genetic drift
  3. Sexual selection
• In sympatric speciation, there has to be a reproductive barrier that isolates a subset of the population in the same area.

  Gene flow to & from the isolated subpopulation is blocked by:

  1. Polyploidy
  2. Sexual selection
  3. Switch in habitat or food source
• We can figure out how long it takes new species to form from broad patterns in:

  1. The fossil record
  2. Morphological data
  3. Molecular data
• The fossil record shows that new species appear suddenly, stay for several strata, & then disappear