Origin of Species

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Origin of Species

• How do we define species?
• A population of organisms that produces viable
  fertile offspring in nature.
• When does this definition fall apart?
• Asexual,extinct and blurred organisms
• What definition is used in these cases?
• Morphospecies concepts

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• What is the main distinction that must occur for
  the origin and integrity of distinct species?
• Reproductive isolation

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• Which sort of reproductive isolation mechanism is
  at work in the following examples?
• Firefly signals with specific flashes to attract
  mates
• male dragonfly has appendages that clasps female
  during mating
• brown trout breed in the fall and rainbow trout
  in the spring
• 1 type of garter snakes lives in the water and
  the other lives on land

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• Horse and donkey produce sterile mule
• frogs that mate and produce offspring that do not
  quite develop

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Biogeography of Speciation

• What is the difference between allopatric and
  sympatric speciation?
• Allopatric speciation involves a geographical
  barrier between 2 groups
• Sympatric speciation is the result of a genetic
  isolation without a geographical barrier

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Conditions for Allopatry

• Peripheral isolate where the fringe organisms are
  already somewhat different from mainstream
  population
• Genetic drift can occur to a small peripheral
  isolate
• The genetic drift continues to change gene pool
  until the group is large
• Natural selection will select the best fit traits
  among the new group to survive

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Ring Species Allopatric Speciation in Progress
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Adaptive Radiation

• Islands are laboratories of speciation
• Adaptive radiation is the evolution a number of
  different new species from a common ancestor
• Archipelago's are the home of adaptive radiations

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What sort of reproductive barrier is this?
Prezygotic
Has reproductive isolation occurred?
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Sympatric Speciation

• Genetic alterations result in a reproductive
  barrier
• Can occur in a single generation
• More frequently seen in plants
• Nondisjunction and selfing leads to polyploidy
• autopolyploid
• alloployploid
• Evolution of wheat

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Sympatric Speciation in Animals
Under normal light
Under monochromatic light
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Genetic Mechanisms of Speciation

• Adaptive Divergence
• reproductive barriers evolve as secondary result
  of divergence
• the barriers evolve to enhance reproduction
  within the group not to eliminate reproduction
  between groups
• reproductive barriers occur as a side effect of
  the accumulated adaptive divergences

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Tempo of Speciation

• Gradualism
• Punctuated Equilibrium

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From Speciation to Macroevolution

• Speciation is the boundary between micro and
  macroevolution
• Cumulative change over vast amounts of time
  accounts for macroevoulution
• How do evolutionary novelties evolve?

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Eye Evolution
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Origin of Novelties

• How do large scale novelties arise?
• Exaptation modifications of older structures
• Pandas thumb stinger of bees etc
• Genetic changes that lead to devlopmental
  changes
• Allometric growth - relative rates of growth
  differs, change one stage and see big change
• Alter timing of developmental events, such as
  sexually active juveniles
• Alteration in homeotic genes
• Evolution, however, is not goal oriented

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• Tetrapod evolution
• Fish Hox gene leads to fin development
• Chicken same Hox gene leads to leg development

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