E v o l u t i o n :     L e c t u r e  # 19 Vocabulary | Study Questions
Natural Selection in Action
Objectives:
  1. Understand the relationship between individual survival and adaptation.

  2. Understand the process of speciation.

  3. Understand the role of isolation barriers in maintaining species integrity.

  4. Understand major concepts in the modern theory of evolution.
  1. Adaptations: genetically controlled, heritable traits that promote survival and reproduction under prevailing conditions.
    Prevailing conditions largely determine whether or not a trait promotes survival and reproduction. So as prevailing conditions change, so do the prevailing traits (adaptations ).
    1. Example: The peppered moth and industrial polution
      In defense against visual predators, a peppered moth's being lighter in color was a more successful trait under the conditions (lighter-colored trees) previous to industrial pollution, which darkened trees with soot. Then the darker moths were better adapted to the prevailing conditions (darker-colored trees), so the prevailing phenotype shifted from lighter moths to darker moths. (Which type of natural selection does this example demonstrate?)
    2. Evolutionary significance of adaptation
      How important are adaptations? 1 - Adaptations come by the process of natural selection working on genetic variation, and are necessary to a species survival. 2 - When the environment (prevailing conditions) changes, previously successful adaptations may prove unsuccessful (be selected against)--resulting in either new, successful adaptations or extinction. 3 - Without sexual reproduction and the genetic variation it generates, life on earth could not survive.
  2. Speciation: a study in evolution
    19.1 Geographic Speciation
    Darwin formed, and many others have since formed ideas about how new species are formed. Geographic speciation is a good idea.
    1. The basic pattern in forming a new species
      (Geographic speciation)
      1. Genetic variation exists among individuals in a population
        (What is(are) the source(s) of genetic variation?) Where there is little or no genetic variation among individuals, a species is in danger because it will be unable to change (adapt) as conditions change.
      2. Genetic variants respond to specific selection pressures
        Natural selection is the product of this relationship, between genetic variants and (biotic and abioitic) selective pressures.
      3. Evolution of unique adaptations
        Unique adaptations come about in response to what? Unique conditions; unique selective pressures.
      4. Reproductive isolation occurs
        Unique adaptations differentiating groups that were formerly of the same species can prevent the interbreeding of individuals across the groups; isolation barriers are formed.
    2. Reproductive isolation barriers
      Physical or behavioral barriers that prevent interbreeding.
      1. Prezygotic mechanisms
        'Prezygotic' - before the zygote; (a zygote is an organism's first cell: when the sperm fertilizes the egg). So prezygotic mechanisms are those that prevent fertilization:
        1. Seasonal and temporal (time) barriers: flowering time
          Example: two closley related cactus plants are fertilized by beetles, which are enticed by nectar into flowers, where they unintentionally pick up and transport gametes to other flowers, bringing about fertilization. When one of the cactus plants flowers at one time (seasonal or the time of day), and another flowers at another time, they are reproductively isolated: fertilization will not take place as only one plants' flowers are available to the beetles at any given time.
        2. Behavioral barriers: mating calls - songs
          When there are behavioral signals corresponding to reproduction, those unable to pick up on these specific signals will be isolated from those that do. (Example: lesser prarie chicken/grouse clip: remember the various mechanisms: tail feather displays, feather coloring, feet stomping, air sac blubbering, etc..)
      2. Postzygotic mechanisms: hybrid sterility
        When species are able to interbreed with other species, fertilization occurs, the product is a hybrid (example: a horse and a donkey will produce a mule (hybrid), which is sterile.) (Hybrid sterility).
    3. Mechanics guiding speciation
      1. Natural selection
        Adaptations come about through the the process of natural selection, which causes allele frequencies to change resulting in unique adaptations.
      2. Reproductive isolation
        Once unique adaptations are in place, strong selection pressures against interbreeding preserve them (from being 'polluted' by foreign, likely maladaptive, adaptations).