Origin of Species

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Chapter 24

• Origin of Species

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Speciation

• Darwin was intrigued with how new species arise
• Fossil record chronicles two patterns of
  speciation
• Anagenesis and cladogenesis

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What is a Species?

• Biological species concept species is a
  population or group of populations whose members
  have the potential to interbreed and produce
  viable offspring, and cant produce viable
  offspring with different species.
• IE genetically isolated from other groups
• Therefore the concept hinges on reproductive
  isolation

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Reproductive Isolation

• Prezygotic impede mating by hindering
  fertlization
• Habitat isolation live in different areas of
  the same region
• Behavioral isolation mating signals are
  different among species
• Temporal isolation breeding times are different
• Mechanical isolation anatomically incompatible
• Gametic isolation sperm cant fertilize egg

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Reproductive Isolation

• Postzygotic
• Reduced hybrid viability offspring die as
  embryos or are frail when born
• Reduced hybrid fertility offspring are not
  viable
• Hybrid breakdown offspring are fertile but
  their offspring cant mate with their generation
  or parental generation

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Problems with Biological Species Concept

• Extinct forms of life we cant check their
  reproductive isolation
• Asexual organisms bacteria

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Proposed Species Concepts

• Ecological species concept defines species
  based on their role in a niche
• Pluralistic species concept combines biological
  and ecological species concept, depending which
  one works best
• Morphological species concept characterizes
  species based on unique structures
• Genealogical species concept defines species
  based on genetic markers

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Modes of Speciation

• How does a single species give rise to different
  species
• Different species are reproductively isolated
• Which means that their genes are incompatible
• All the isolations come back to genetics

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Allopatric Speciation

• Speciation which takes place in populations that
  are geographically isolated
• Many events can separate a population of
  individuals
• Mountain range forms, individuals may be blown
  out to an island, land bridges may form, canyons
  may form

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Adaptive Radiation

• Islands are living laboratories for study of
  speciation

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Geographic isolation and Reproductive Isolation

• Geographic Isolation does not qualify as
  reproductive isolation in the biological sense
• Geographic Isolation only incubates reproductive
  isolation
• Or produces it
• Monkey face plant experiment
• Its not that selection favors a reproductive
  barrier between allopatric populations, but there
  is no longer any advantage to the absence of such
  barriers

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Summary of Allopatric Speciation

• New species from while they are isolated
• Due to the gene pool evolves by genetic drift and
  natural selection
• Such differences form reproductive barriers even
  if the populations merge again

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Sympatric Speciation

• Sympatric speciation new species arise within
  the range of parent populations
• This means that new species arise even in the
  absence of physical barriers

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Sympatric Polyploid Speciation

• New species of plants arise due to increase of
  chromosome number
• Plants are able to do this because they can self
  pollinate themselves or reproduce asexually
• Autopolypliody
• allopolyploidy

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Sympatric Speciation in Animals

• Polyploid occurs in animals but is less common
• Other factors are ecological separation
• One group begins using a different niche
• Wasps and fig trees
• Non random mating
• Females choose mates based on some characteristic
  that other members of the group dont have
• Cichlids and lake victoria

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Punctuated Equilibrium

• Fossil records show organisms that remain
  unchanged for many years and then disappear where
  new forms suddenly appear
• This is explained through allopatric speciation
• As a population becomes separated it becomes a
  new form and eventually it may revisit the parent
  population where it outcompetes or where the
  parent population has gone extinct

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Punctuated Equilibrium
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Most Evolutionary novelties are modified versions
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Evolution is not goal oriented

• Evolution only selects organisms that are best
  suited to a particular environment
• The ones that are around today are the ones that
  have the best possible sets of adaptations

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