Transcript Development and Evolutionary Change Chapter 21

Development
and
Evolutionary Change
mammalian
limb bones are
homologous
Figure 1.2
bones are,
wings aren’t
Figure 25.2
leaf homologs
Figure 25.3
Homologous larval stages
Figure 21.1
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
fruit fly
“leg-eye” formed
by mouse Pax6
gene
Figure 21.2
anterior/
posterior
development
Figure 21.3
Mutations in homeobox genes
Figure 21.4
-Ubx
-Hoxc-8
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 misassignment of segment identities
many diverse developmental programs are
initiated by a few common instructions
but, once initiated, the programs produce
vastly different structures
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
arthropod use of Ubx
Figure 21.5
foot making - chicks & ducks
Figure 21.6
BMP4
Gremlin apoptosis webbing
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
Chicken foot webs
Figure 21.7
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 module’s development
doesn’t alter development of another
terrestrial
arboreal
Figure 21.8
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
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
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
cooler soil
temperatures
precede the
dry season
warmer soil
temperatures
precede the
dry season
Bicyclus pupation
Figure 21.9
Evolution and Development
• exogenous signals affect development
– seasonal temperature variations
• pupation produces a dry-season or a wetseason adult Bicyclus butterfly
–pupal soil temperature determines the
adult form
– seasonal day length variations trigger
developmental changes in other animals and
in plants
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
1st year twig
Figure 21.10
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
Daphnia - with & without a helmet
Figure 21.11
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
bean etiolation
Figure 21.12
Evolution and Development
• exogenous signals affect development
– plant seedlings in low light exhibit lightseeking development (etiolation)
• small, pale leaves; long spindly stems
– when light is encountered, tissues return to
normal photosynthetic development
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
constant
plastic
Figure 21.13
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