Download EVOLUTIONARY DEVELOPMENT AND THE INSECT BODY PLAN

EVOLUTIONARY
DEVELOPMENT
AND
THE
INSECT
BODY
PLAN
Sean
Beplate
Bio
348
2/5/10
The
Study
of
“Evo‐Devo”…What
Is
It?
•  EvoluQonary
development
(aka
phylontogeneQcs)
is
a
product
of
both
evoluQonary
and
developmental
biology.
•  This
field
uQlizes
phylogenies
and
ancestral
relaQonships
to
examine
the
course
of
evoluQon
for
developmental
processes
of
interest.
(Embryonic
development
is
a
common
component)
•  With
respect
to
arthropods,
evo‐devo
has
also
drawn
from
the
fields
of
entomology,
carcinology,
and
geneQcs
What
is
THE
GOAL
of
Arthropod
Evo‐
Devo?
•  Arthropods
exhibit
extreme
diversity
of
both
morphology
and
body
plans
•  The
evo‐devo
approach
aaempts
to
provide
a
framework
for
the
development
of
this
diversity,
looking
at
both
molecular
and
morphological
evidence
The
Concept
of
a
Body
Plan
•  Richard
Owen
originally
described
“body
plan”
as
“a
paaern
of
anatomical
organizaQon
shared
by
a
group
of
animals.”
•  The
term
“bauplan”
was
coined
by
Joseph
Henry
Woodger
to
describe
“a
collecQon
of
homologous
anatomical
features
seen
across
the
natural
history
of
a
group.”
•  Currently,
“body
plan”
has
expanded
to
include
both
of
these.
WHAT
ARE
THE
FEATURES
OF
THE
ARTHROPOD
BODY
PLAN?
Arthropod
Body
Plan
•  Protostomes
with
segmented
bodies
•  Appendages
are
also
segmented;
each
segment
has
its
own
muscular
structure
and
individual
innervaQon
•  Have
a
cuQcle
that
is
shed
during
growth
•  Exhibit
tagmosis,
providing
the
capability
for
specialized
behaviors
•  Insects
exhibit
the
most
consistent
tagmaQc
paaern:
head
composed
of
fused
segments,
thorax
of
three
segments,
and
an
abdomen
of
11/12
segments
Hox
Genes
•  Hox
genes=
homeoQc
complex
genes
•  Are
transcripQon
factors
with
sequences
well
conserved
throughout
most
animals
•  Serve
as
regulators
of
segment
idenQty
within
the
arthropods.
Because
of
this,
they
dictate
organizaQon
of
body
plan
in
embryonic
ectoderm.
•  Overlap
of
these
genes
code
for
a
different
segment
than
if
read
separately.
•  Arthropods
have
10
ancestral
Hox
genes
Paaerns
of
Hox
Gene
Expression
•  Looking
at
the
spider,
a
nested
paaern
(large
amounts
of
overlap)
is
present
in
both
the
prosoma
and
opisthosoma.
Looking
at
the
Mandibulata
(insect
and
crustacean
examples,)
there
is
much
less
overlap.
It
is
likely
that
that
this
facilitates
the
specialized
head
appendages
–
less
overlap
in
crustaceans
corresponding
to
a
greater
number
of
feeding
appendages.
Difference
in
Chelicerata
(prosoma
and
opisthosoma)
body
plan
and
Insecta
(head,
thorax,
and
abdomen)
body
plan.
Increased
Hox
gene
overlap
likely
contributed
to
the
fewer
segments
seen
in
the
Chelicerata.
example
of
the
obvious
difference
in
number
of
head
appendages
between
insects
and
crustaceans
(Australian
bull
ant
vs.
cardinal
shrimp)
Drosophila
melanogaster
(DmUbx)
and
Artemia
franciscana
(AfUbx)
Ubx
protein
sequence.
The
uncolored
regions
demonstrate
blocks
of
differences
in
sequence
MutaQon
of
Hox
Genes
and
Hexapod
Limb
Paaern
•  Averof
&
Akam
postulated
that
the
hexapod
body
plan
resulted
from
mutaQons
restricQng
Ubx
and
AbdA
expression
to
proto‐abdomen
region.
Secondly,
mutaQon
of
these
genes
caused
their
expression
to
suppress
limb
development.
•  Ronshaugen
study
first
looked
at
Ubx
protein
sequence
in
Drosophila
melanogaster
and
Artemia
franciscana
(a
crustacean)
Results
of
the
Ronshaugen
Study
•  Ubx
from
Artemia
and
Drosophila
both
demonstrated
similar
suppression
of
the
development
of
head
structures
in
the
thorax
of
embryonic
Drosophila
•  Big
difference:
Drosophila
Ubx
suppressed
all
embryonic
limb
development
on
thorax,
while
Artemia
Ubx
only
suppressed
15%
•  Proposal:
Hexapod
body
plan
resulted
from
mutaQons
located
at
C‐terminal
residues.
DISCUSSION
TIME!
•  The
Ronshaugen
paper
suggested
that
the
removal
of
Ser/Thr
residues
produced
novel
phenotypes.
How
might
such
a
development
have
been
evoluQonarily
propagated?
(keep
in
mind
the
phylogenies
presented
in
these
readings)
•  Amer
reading
these
papers,
can
you
think
of
any
reasons
that
six
would
have
been
an
advantageous
number
of
limbs
for
early
insects
to
possess?
Hox
Gene
Expression
and
Insect‐
Specific
Development
Hox
Gene
Expression
and
Insect‐
Specific
Development
•  Because
insects
are
unique
in
their
ability
to
fly,
wing
evoluQon
is
currently
being
studied
extensively
•  Two
main
hypotheses:
–  1)
Wings
developed
as
dorsolateral
outgrowths
before
arQculaQon
and
muscle
connecQon.
–  2)Wings
developed
from
dorsal
projecQons
proximally
located
on
legs
and
appendages
of
early
insects.
Which
Hypothesis
is
More
Accurate?
•  Averof
&
Cohen
study
tested
this,
using
the
proteins
derived
from
the
genes
Pdm
and
Ap
•  Pdm
and
Ap
proteins
were
detected
in
distal
epipods
in
Artemia
franciscana
(a
branchiopod)
•  Pdm
protein
was
also
detected
in
the
epipod
of
Pacifastacus
lenisculus
(a
crawfish)
Hox
Genes
and
Modern
Insect
Wings
•  Early
wings
were
present
on
all
segments
of
the
thorax
and
abdomen.
Juvenile
insects
also
possessed
wings.
•  Since
the
emergence
of
wings,
they
have
become
reduced
in
the
insect
body
plan,
resulQng
from
Hox
gene
induced
repression
•  Scr
has
been
found
to
suppress
wing
development
in
prothorax
of
Drosophila
embryos,
and
Ubx
and
Abd‐A
suppress
in
the
abdomen
DISCUSSION
TIME!
•  Another
key
feature
of
the
insect
body
plan
is
the
lack
of
abdominal
limbs
in
addiQon
to
the
lack
of
abdominal
wings.
Arachnids
also
do
not
have
any
limbs
on
their
“abdomen‐like”
segment.
What
kind
of
Hox
gene
interacQons
and
expression
paaerns
could
underlie
this?
Winglessness
of
Hymenoptera
•  Hymenoptera
are
social
insects,
meaning
that
they
live
in
colonies
with
castes
that
fulfill
different
roles.
•  What
makes
this
interesQng?
Ants
with
wings
and
acts
that
lack
wings
exhibit
the
same
genes!
Background
–
Ant
Castes
•  Queen
–
Female.
Possesses
wings.
One
job–
to
mate
and
lay
eggs.
•  Male
–
Possesses
wings.
ReproducQve.
•  Soldiers
–
Non‐
reproducQve.
Protect
the
nest
•  Workers–
Non‐
reproducQve.
Forage,
maintain
nest,
and
care
for
eggs.
JH
and
Ant
Development
•  As
larvae,
if
enough
nutriQon
is
available
to
an
individual,
juvenile
hormone
(jh)
accumulates
to
a
level
high
enough
to
develop
wings
during
the
pupal
stage.
If
not
enough
jh
gets
produced,
the
ant
will
be
non‐reproducQve.
•  In
ants
with
soldier
castes,
a
second
JH
checkpoint
determines
caste.
Forewing
discs
develop
in
the
pupal
stage
of
soldiers,
but
are
programmed
to
die
FINAL
DISCUSSION
QUESTIONS
•  How
do
you
think
that
Hox
gene
organizaQon
could
have
aaributed
to
the
development
of
insect
heads
from
fused
segments?
•  If
the
Ronshaugen
study
was
to
be
repeated,
what
organisms/developed
structures
would
it
be
helpful
to
include
as
a
comparison?
•  Synthesizing
the
informaQon
presented
in
each
paper,
what
developments
in
insect
body
plan
do
you
think
may
have
followed
the
“hopeful
monster”
method?
What
do
you
think
followed
a
more
gradual
progression?