Lesson 3

• Species


  Groups of interbreeding natural populations that are reproductively isolated from other such groups (Ernst Mayer's definition)
• New species formation


  Caused by a series of evolutionary processes which cause reproductive isolation
• Allopatric speciation or geographic speciation


  Occurs when some members of a population become geographically separated from the other members thereby preventing gene flow
• Sympatric speciation


  Occurs when members of a population that initially occupy the same habitat within the same range diverge into two or more different species
• Parapatric speciation


  Occurs when the groups that evolved to be separate species are geographic neighbors. Gene flow occurs but with great distances is reduced
• Carolus Linnaeus


  A Swedish botanist who worked on the order in the diversity of life; hierarchy of taxonomic categories and classification of plants
• Thomas Malthus


  An Economist and clergyman who published an Essay on the Principle of Population, stating that populations had an inherent tendency to increase geometrically, while the resources needed to support this growth increase slowly or not at all
• Georges Cuvier


  A French anatomist, naturalist, writer and a paleontologist who strongly opposed the concept of evolution and proposed Catastrophism
• James Hutton


  A Scottish geologist who proposed that geological change occurred slowly but continuously by the process of Gradualism
• Charles Lyell


  A Scottish lawyer turned geologist who published Principles of Geology, proposing Uniformitarianism - the processes that alter the Earth are uniform through time
• Jean Baptiste Lamarck


  A French biologist who proposed that modern species descended from other species, and his theory on evolutionary change included the Principle of use and disuse and Inheritance of acquired characteristics
• Charles Darwin


  Credited in the development of the theory of evolution through natural selection, along with Alfred Russel Wallace
• Neo-Darwinian theory or Modern Synthesis


  A unified theory of evolution that incorporates Mendel's research on genetics and how various characteristics coded in an individual's DNA can be passed on to successive generations
• Post-zygotic isolation mechanisms allow fertilization but nonviable or weak or sterile hybrids are formed. 


  • Hybrid inviability
  • Hybrid infertility/sterility
  • Hybrid breakdown
• Pre-zygotic isolation mechanisms prevent fertilization and zygote formation.


  • Geographic or ecological or habitat isolation
  • Temporal or seasonal isolation
  • Behavioral isolation
  • Mechanical isolation
  • Gametic isolation
• Potential mates occupy different areas or habitats or environments thus, they never come in contact.


  Geographic or ecological or habitat isolation
• Different groups may not be reproductively mature at the same season, or month or year. Active or fertile at different times.

  Temporal or seasonal isolation
• Patterns of courtship are different or different courtship activities.


  Behavioral isolation
• Differences in reproductive organs prevent successful interbreeding or mating organs or pollinators incompatible.


  Mechanical isolation
• Incompatibilities between egg and sperm prevent fertilization or gametes cannot unite.


  Gametic isolation
• Fertilized egg fails to develop past the early embryonic stages or hybrid offspring fail to reach maturity.


  Hybrid Inviability
• Hybrids are sterile because gonads develop abnormally or there is abnormal segregation of chromosomes during meiosis. Hybrid offspring unable to reproduce.


  Hybrid infertility/sterility
• Identify:

  Ecological isolation

  
• Identify:

  Behavioural isolation

  
• Identify:

  Temporal isolation

  
• Identify:

  Mechanical isolation

  
• Identify:


  Hybrid inviability

  
• Identify:


  Hybrid infertility

  
• Identify:

  Hybrid breakdown

  
• Examples of geographic speciations are:

  • Bodies of water
  • Mountain ranges
• Example of sympatric speciation is change in chromosome number (polyploidization).
• •There is also abrupt change in the environment over a geographic border and strong disruptive selection must also happen.


  Parapatric speciation
• allo – other, patric – place; ‘other place’
• sym – same, patric – place; ‘same place’
• para – beside, patric – place; ‘beside each other’
• 3 Modes of Speciation

  1. Allopatric speciation or geographic speciation
  2. Sympatric speciation
  3. Parapatric speciation
• Carolus Linnaeus published Species Plantarum (~7,300 plants)
• F1 hybrids are normal, vigorous and viable, but F2 contains many weak or sterile individuals. Second –generation hybrid offspring have reduced fitness.



  Hybrid breakdown
• According to Thomas Malthus, Populations had an inherent tendency to increase geometrically, while the resources needed to support this growth increase slowly or not at all.
• According to Charles Lyell, Uniformitarianism is the process that alter the Earth are uniform through time.