The Origin of Species Macroevolution

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The Origin of SpeciesMacroevolution
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Biological Species Concept

• Ernst Mayr, 1942
• defines species as a population who have the
• potential to interbreed.
• Must be able to interbreed in nature
• Produce viable, and fertile offspring
  (interfertility)
• Must occur in nature

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Prezygotic Barriers
Factors that impede mating between species or
hinders fertilization.

• Habitat Isolation contact is rare b/w species
• because of habitat location
• Behavioral Isolation attractor signals are not
  the
• same between the species
• Temporal Isolation breeding occurs at different
• times, seasons, years.
• Mechanical Isolation mating can be attempted
  but
• not successful.
• Gametic Isolation fusion b/w gametes does not
• occur

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Postzygotic Barriers
Barriers that prevent a fertilized egg from
developing into a viable, fertile adult.

• Reduced Hybrid Viability development is not
• complete, or survivors are weak.
• Reduced Hybrid Fertility hybrids are sterile,
• gametes are not formed by meiosis. (Mule).
• Hybrid Breakdown 1st generations are viable and
• fertile, but next generations are feeble or
  sterile.

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Modes of Speciation
Allopatric Speciation a geographical barrier
that isolates populations and prevents gene
flow. Sympatric Speciation chromosomal changes
and non- random mating changes gene flow within
a pop.
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Ring Species in Progress?
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Conditions favoring Allopatric Speciation

• Gene pools differ between the outer population
• extreme clines created, differ from inner pop.
• Outer pop small ? founder effect
• Genetic Drift occurs until outer pop. is large
• enough. Some may become fixed, causing more
• divergence.
• Evolution by Natural Selection may differ between
• outer and inner pop.

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Sympatric Speciation
Polyploidy Creation of a new species when
during cell division extra sets of chromosomes
are generated. Occurs in plants species.
Autopolyploidy failure of meiosis results in
4n. Can self fertilize or mate with other
4ns. Sterile offspring made when fertilize a
2n. Discovered by Hugo de Vries in 1900s,
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Allopolyploid two species contribute to a
polyploid hybrid. Two different species
interbreed. Propagation by asexual
reproduction. May be more vigorous than
parents, best of both.
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Sympatric Speciation

• Reproductive Isolation
• Different Figs, different wasps
• Monkey Fig
• Lake Victoria, East Africa
• Selective reproduction (blue back vs. Red back)
• Mate choice based on color is main repro.
  Isolation
• Can still interbreed..if prezygotic barrier is
  breached.
• Speciation recent.

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Tempo of Speciation

• Gradualism
• Slow divergence
• Slight changes

• Punctuated Equilibrium
• Abrupt changes
• Period of stasis

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Evo-Devo

• Interdisciplinary science b/w evolutionary
  biology and study of development.
• Genes regulate (zygote to adult)
• Control rate
• Timing
• Spatial pattern of change in form
• Allometric growth
• Growth rates of different parts
• Changes form/structure
• Heterochrony evolutionary change in the rate or
  timing of developmental events

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Paedomorphosis

• At sexual maturity, species may retain body
  features that were juvenile structures in
  ancestral species.
• Salamanders have larval stage to become adult.
• Some become mature but still have gills and other
  structures (juvenile)

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Evolution is not goal oriented.