Chapter 16 The Origin of Species

1

• Chapter 16 The Origin of Species

2
Macroevolution the origin of new taxonomic groups

• Speciation the origin of new species
• 1- Anagenesis (phyletic evolution) A pattern of
  evolution that results in linear descent with no
  branching or splitting of the population -
  accumulation of heritable changes
  
• 2- Cladogenesis (branching evolution) The
  evolutionary change and diversification resulting
  from the branching off of new taxa from common
  ancestral lineages budding of new species from a
  parent species that continues to exist (basis of
  biological diversity)

3
What is a species?

• Biological species concept a population or
  group of populations whose members have the
  potential to interbreed and produce viable,
  fertile offspring (genetic exchange is possible
  and that are reproductively isolated from other
  such populations)

4
Reproductive Isolation (isolation of gene pools),
I

• Prezygotic barriers (Premating Isolation)
  impede mating between species or hinder the
  fertilization of the ova
• Geographical (separation of populations by a
  physical barrier )
• Behavioral (lack if interbreeding between
  pollutions of animals that differ in courtship
  and mating rituals)
• Temporal (inability of populations to interbreed
  because of different breeding seasons)
• Mechanical (inability of male and female
  organisms to exchange gametes because of
  incompatibility)
• Ecological (lack of interbreeding between
  populations that occupy distinct habitats within
  the same general area)

5
Reproductive Isolation, II

• Postzygotic barriers( Post mating Isolation)
  fertilization occurs, but the hybrid zygote does
  not develop into a viable, fertile adult
• Gametic Incompatibility the inability of sperm
  from one population to fertilize eggs of another
• Hybrid infertility - reduced hybrid fertility
  (mule horse x donkey cannot backbreed)
• Hybrid inviability- the failure of a hybrid
  offspring of two different populations to survive
  (cotton 2nd generation hybrids are sterile)

6
Modes of speciation (based on how
gene flow is interrupted)

• Allopatric populations segregated by a
  geographical barrier can result in adaptive
  radiation when a species gives rise to many new
  species in relatively a short period of time
  (island species- when populations of a single
  species invade a variety of new habitats and
  evolve in response to the differing environmental
  pressures)
• Little or no gene flow occurs and if pressures of
  natural selection differ in the separation
  locations, then populations may accumulate
  genetic differences

7
Modes of speciation (based on how
gene flow is interrupted

• Sympatric reproductively isolated subpopulation
  in the midst of its parent population (change in
  genome) polyploidy in plants (the acquisition of
  multiple copies of each chromosome)

8
What causes Extinction?

• Extinction natural phenomenon, however, rate is
  of concern..
• 50 loss of species when 90 of habitat is lost
• Major Threats
• Habitat destruction single greatest threat
  cause of 73 of species designation as extinct,
  endangered, vulnerable, rare 93 of coral reefs

9
What causes Extinction?

• Competition by exotic (non-native) species
  cause of 68 of species designation as extinct,
  endangered, vulnerable, rare travel
• Overexploitation commercial harvest or sport
  fishing illegal trade