Development and Evolutionary Change

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Development and Evolutionary Change
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mammalian limb bones arehomologousFigure 1.2
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bones are, wings arentFigure 25.2
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leaf homologsFigure 25.3
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Homologous larval stagesFigure 21.1
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Evolution and Development

• evolutionary biology explains similarities among
  related organisms
• homologous structures are inherited from a common
  ancestral structure
• some homologies are visible in immature stages
• due to homologous developmental processes
• many shared developmental processes are guided by
  homologous genes

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fruit flyleg-eye formed by mouse Pax6
geneFigure 21.2
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anterior/posterior developmentFigure 21.3
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Mutations in homeobox genesFigure 21.4
-Hoxc-8
-Ubx
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Evolution and Development

• homeobox genes guide segmentation in insects and
  mammals
• Drosophila ems, tll otd and mammalian homologs
  guide anterior brain development
• mutations in homeobox genes result in
  mis-assignment of segment identities
• many diverse developmental programs are initiated
  by a few common instructions
• but, once initiated, the programs produce vastly
  different structures

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Evolution and Development

• differences in related organisms are due to
  developmental changes in the past
• arthropods all use the Ubx gene in development
• insect Ubx is mutated to prevent leg formation in
  the abdomen
• insects have no abdominal legs
• other arthropods have abdominal appendages

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arthropod use of UbxFigure 21.5
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foot making - chicks ducksFigure 21.6
BMP4
Gremlin
apoptosis
webbing
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Evolution and Development

• most birds develop without webbed feet
• ducks retain their webs
• BMP4 induces apoptosis in the cells of developing
  feet
• Gremlin inhibits BMP4 to retain tissue around the
  digits of chicken feet
• Gremlin inhibits BMP4 in duck web tissues as well
• Gremlin inhibits BMP4 in chicken webs when
  applied experimentally

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Chicken foot websFigure 21.7
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Evolution and Development

• heterochronic changes and modular development
  have reshaped salamander feet
• when larval de-webbing of the feet is inhibited,
  adults retain juvenile feet
• different modules develop independently
• a change in one modules development doesnt
  alter development of another

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terrestrial arborealFigure 21.8
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Evolution and Development

• Plants and animals are different
• plant embryonic development does not involve cell
  migration
• plant development is indeterminate meristems
  constantly add to or replace modules
• development is very plastic - responsive to
  environmental impacts

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Evolution and Development

• plants and animals are different, but
• plants and animals share some developmental genes
• MADS box genes and homeobox genes
• the shared developmental genes guide entirely
  different programs
• animals are motile and develop accordingly
• plants are sessile and develop accordingly

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Evolution and Development

• development is the product of the complex
  interactions of gene products
• expressed in response to informative signals
• endogenous signals
• exogenous signals that are predictive

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Bicyclus pupationFigure 21.9
cooler soil temperatures precede the dry season
warmer soil temperatures precede the dry season
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Evolution and Development

• exogenous signals affect development
• seasonal temperature variations
• pupation produces a dry-season or a wet-season
  adult Bicyclus butterfly
• pupal soil temperature determines the adult form
• seasonal day length variations trigger
  developmental changes in other animals and in
  plants

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Evolution and Development

• exogenous signals affect development
• different food sources
• Nemoria moth caterpillars eat oak catkins in the
  spring oak leaves in the summer
• spring caterpillars resemble catkins
• summer caterpillars resemble young twigs

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1st year twigFigure 21.10
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Evolution and Development

• exogenous signals affect development
• Daphnia developing in the presence of predatory
  fly larvae grow defensive helmets
• Daphnia without helmets reproduce more efficiently

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Daphnia - with without a helmetFigure 21.11
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Evolution and Development

• exogenous signals affect development
• Spadefoot toads lay eggs in ephemeral pools
• some years, nursery pools dry up before
  development is complete
• tadpole development changes in response to
  increased crowding
• mouth size and jaw muscle strength increase
• bigger, tougher tadpoles cannibalize weaker
  siblings, increasing chances of maturing

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bean etiolationFigure 21.12
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Evolution and Development

• exogenous signals affect development
• plant seedlings in low light exhibit
  light-seeking development (etiolation)
• small, pale leaves long spindly stems
• when light is encountered, tissues return to
  normal photosynthetic development

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Evolution and Development

• exogenous signals affect development
• different modules respond differently
• numbers of seeds produced varies in response to
  environmental conditions
• seeds size tends to remain constant

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constantplasticFigure 21.13
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Evolution and Development

• exogenous signals affect development
• not all signals cause responses
• developmental responses are acquired through
  repeated exposure to informative signals
• uninformative signals are ignored
• developing organisms cannot respond to novel
  signals