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Transcript
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
• What is the main distinction that must
occur for the origin and integrity of
distinct species?
• Reproductive isolation
• 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
• Horse and donkey produce sterile mule
• frogs that mate and produce offspring
that do not quite develop
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
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
Ring Species: Allopatric Speciation in
Progress
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
What sort of reproductive barrier is this?
Prezygotic
Has reproductive isolation occurred?
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
Sympatric Speciation in Animals
Under normal light
Under monochromatic light
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
Tempo of Speciation
• Gradualism
• Punctuated Equilibrium
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?
…
Eye
Evolution
Origin of Novelties
• How do large scale novelties arise?
• Exaptation = modifications of older
structures
– Panda’s 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
• Tetrapod
evolution
– Fish; Hox gene
leads to fin
development
– Chicken; same
Hox gene leads
to leg
development