This study analyzed variability in vertebral length among ecologically diverse populations of threespine stickleback fish. The researchers measured vertebral length and body length from x-rays of over 20 stickleback populations. They found that vertebral length declines along the vertebral column from front to back. Populations with longer bodies tended to have longer vertebrae. Limnetic populations in deep lakes had longer vertebrae than benthic/stream populations. Vertebral length also decreased with increasing vertebral number. Overall, the study uncovered patterns of vertebral length variation between stickleback populations adapted to different environments.

1. § The threespine stickleback has long been a staple organism in the study of
evolution because of its ecological and morphological diversity
§ Past research has highlighted the difference of vertebral number between forms
and found that it increases with body elongation (with some exceptions).
§ This study aims to analyze variability in vertebral length in ecologically diverse
populations of threespine stickleback
§ Vertebral length may be an important factor in a fish’s mobility. With shorter
vertebrae, the threespine stickleback should able to laterally bend to a greater
degree and increase its burst swimming performance.
Introduction:
Objectives:
1. Describe
the
relationships
between
vertebral
length
and
the
length
of
the
body
in
threespine
stickleback
2. Examine
whether
vertebral
length
changes
along
the
vertebral
column
3. Examine
the
relationship
between
vertebral
length
and
vertebral
number
4. Investigate
how
vertebral
length
varies
between
populations
with
different
body
forms
Results: Results:
Variation
in
Body
Forms:
Limnetic:
Benthic
and
Stream
populations
are
characterized
by
their
deeper
body
forms
and
are
found
in
shallow
lakes
and
streams.
Anadromous
populations
are
the
ocean
form
of
the
threespine
stickleback,
known
for
their
large
size
and
armored
plates.
Benthic/Stream:
Anadromous:
Limnetic
populations
are
generally
found
in
deep
lakes
and
are
characterized
by
their
elongate
body
form.
Tinkering
with
the
Axial
Skeleton
II:
Uncovering
Vertebral
Length
Variation
in
the
Threespine
Stickleback
Twenty
populations
of
the
threespine
stickleback
were
collected
from
nineteen
bodies
of
water
in
Alaska
and
were
brought
to
the
Field
Museum
of
Natural
history
for
photography
and
x-­‐ray.
The
photographs
and
x-­‐rays
were
then
scaled
and
measured
for
standard
(body)
length,
body
depth,
and
vertebral
length
using
the
computer
program
TPSDig2.
Standardizing
vertebral
length
by
body
length:
• Vertebral
length
was
standardized
by
body
length
to
account
for
variation
attributable
to
differences
in
body
size
among
specimens.
This
was
done
by
regression
analysis
and
the
calculation
of
residuals.
Residuals
are
the
difference
between
the
measured
value
and the
predicted
value.
The
predicted
value
for
each
fish
was
added
to
the
calculated
residual
to
standardize
by
size.
A
grand
mean
was
also
necessary
for
these
calculations.
However,
the
anadromous
populations
tend
to
be
much
larger
than
the
benthic/stream
and
limnetic
populations.
To
ensure
accuracy,
two
separate
grand
means
for
standard
length
were
calculated:
one
for
benthic/stream
and
limnetic
populations
(45.64
mm),
and
one
for
the
anadromous
populations
(69.50
mm).
Data
on
the
anadromous
populations
is
not
shown
here.
Procedures
and
Statistical
Methods:
Figure
1
shows
the
size-­‐adjusted
vertebral
length
values
for
vertebrae
AV1-­‐CV3
as
a
function
of
total
vertebral
number
separated
by
benthic/stream
(B)
and
limnetic
(L)
populations.
Objective
2:
• Looking
vertically
down
each
column,
it
can
be
seen
that
there
is
a
decline
in
size-­‐
adjusted
vertebral
length
moving
posteriorly
along
the
body
axis
from
AV1
to
CV3.
AV1
is
the
longest
vertebra,
followed
by
AV2.
AV3,
CV1,
and
CV2
tend
to
have
similar
size-­‐adjusted
values,
while
CV3
consistently
shows
a
much
lower
value.
Objective
3:
• As
vertebral
number
goes
up,
vertebral
length
declines
in
both
the
benthic
and
limnetic
populations.
However,
the
CV3
length
in
the
limnetic
populations
with
34
vertebrae
increases
slightly.
Objective
4:
• This
graph
is
also
useful
for
examining
differences
in
vertebral
length
between
limnetic
and
benthic
populations.
Overall
the
graph
shows
benthic
and
stream
populations
having
a
lower
size-­‐adjusted
vertebral
length
than
the
limnetic
populations.
Kirby
Karpan
and
Windsor
Aguirre
Department
of
Biological
Sciences,
DePaul
University,
Chicago,
Illinois
Vertebral
Length
Along
the
Body
Axis:
Figure
1:
Rather
than
doing
statistical
analysis
on
all
vertebrae,
twelve
vertebrae
spanning
the
entire
vertebral
column
were
measured. The
first
two
abdominal
vertebrae
were
averaged
and
called
AV1.
The
middle
two
abdominal
vertebrae
were
averaged
and
called
AV2,
and
the
last
two
abdominal
vertebrae
were
averaged
and
called
AV3.CV1,
CV2,
and
CV3
were
calculated
in
the
same
way
for
the
caudal
vertebrae.
Figure
3:
Objective
1:
Figure
3 shows
vertebral
length
of
AV1-­‐CV3
plotted
as
a
function
of
standard
(body)
length.
Specimens
are
color
coded
by
ecomorph.
It
can
be
seen
that
vertebral
length
is
more
strongly
correlated
for
vertebrae
AV1-­‐CV2,
and
that
the
posterior
end,
CV3,
exhibits
greater
variation.
However,
vertebral
length
is
generally
strongly
correlated
with
standard
length.
In
terms
of
the
four
objectives,
it
has
been
seen
that:
1)
Larger
fish
have
longer
vertebrae,
with
R2 values
ranging
between
0.70
and
0.94.
For
most
vertebrae,
the
R2 values
were
0.87
or
greater,
indicating
a
strong
relationship
between
vertebral
length
and
body
length.
For
CV3,
the
relationship
was
weaker,
indicating
greater
variability
in
this
region.
2)
Vertebral
length
declines
posteriorly
along
the
vertebral
column.
However,
the
pattern
of
decline
is
not
uniform.
AV3,
CV1,
and
CV2
tend
to
be
similar
in
length.
The
largest
decline
is
consistently
between
CV2
and
CV3,
indicating
substantial
decline
in
vertebral
length
at
the
very
end
of
the
vertebral
column.
3)
Vertebral
length
generally
declines
as
vertebral
number
increases
in
both
benthic
and
limnetic
populations.
Surprisingly,
vertebral
length
increased
between
fish
with
30
and
31
vertebrae.
4)
Deeper
bodied
benthic/stream
populations
have
shorter
vertebrae
than
the
more
elongate
limnetic
populations
for
all
vertebral
counts.
The
difference
in
vertebral
length
was
particularly
pronounced
for
fish
with
33
vertebrae.
Thanks
to
The
Field
Museum
of
Natural
History
and
all
involved
in
this
project.
Conclusions:
Results:
Figure
2: In
Figure
2,
vertebral
length
was
averaged
across
all
vertebrae.
This
figure
is
useful
for
comparing
the
benthic/stream
and
limnetic
stickleback
populations.
Objective
3:
• Vertebral
length
generally
declines
with
increasing
vertebral
number,
with
the
exception
of
fish
with
31
vertebrae.
Objective
4:
• For
all
vertebral
counts,
limnetics
have
longer
vertebrae
than
benthics.
The
benthic/stream
populations
follow
the
limnetic
populations
fairly
closely
save
for
the
large
drop
in
the
benthic/stream
populations
at
33
vertebrae.