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