First published online August 25, 2003
Lung ventilation during treadmill locomotion in a terrestrial turtle, Terrapene carolina
Tobias Landberg1,*,
Jeffrey D. Mailhot2 and
Elizabeth L. Brainerd1,2
1 Graduate Program in Organismic and Evolutionary Biology, University of
Massachusetts Amherst, 611 North Pleasant Street, Amherst, MA 01003,
USA
2 Biology Department, University of Massachusetts Amherst, 611 North
Pleasant Street, Amherst, MA 01003, USA
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Fig. 1. Lateral view of Terrapene carolina illustrating the two main lung
ventilation mechanisms of turtles. Half the shell has been removed to reveal
the internal morphological relationships between the lungs, abdominal muscles
and skeletal elements. (A) Illustration of the abdominal muscles and lungs of
T. carolina. The paired transverse abdominis (TA) muscles wrap around
the posterior portion of the lungs and produce exhalation by compressing the
lungs as they contract. The cup-shaped oblique abdominis (OA) muscles actively
produce inhalation as they flatten and expand the inguinal flank
postero-ventero-laterally. (B) Photograph of the skeleton with limbs and neck
fully extended. Because the shell contains a fixed volume, the lungs can be
filled with air when the head and limbs are protracted. (C) Air can be forced
out of the lungs when the limbs and head are retracted into the shell. Our
recordings show that when T. carolina is in this fully retracted
position, some air remains in the lungs and breathing is possible with the use
of the abdominal muscles.
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Fig. 2. Pneumotach mask construction. (A) A small amount of clay (cl) is placed
over the turtle's nares. (B) Dental impression material is applied over the
clay and face (avoiding lower jaw; turtle breathes through the mouth during
this phase). The mask is then removed and trimmed and the breathing port (bp)
is inserted. (C) Clay is placed over the mouth, dental impression material is
reapplied (over the mouth but not the nares; turtle breathes through the nares
during this phase) and the previous mask is pressed into place. Once the
composite mask has cured and been trimmed, it is attached with surgical
adhesive on the day of the experiment and the pneumotach (pn) is inserted into
the breathing port.
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Fig. 3. Footfall diagrams of Terrapene carolina (individual 01) from bouts
of treadmill locomotion. (A) Limb support (solid bars) and ventilatory airflow
(red trace) during two bouts of locomotion. Note the short pause between the
bouts of locomotion. (B) Polar diagram showing the relative timing of limb
support (mean ± S.D.). Each solid bar represents a different
limb and is shown in the same shade of grey as in the previous panel. Each
stride cycle (from Fig. 3A) is
normalized to 360° so that the end of left hindlimb support is always at
0° (top of circle) and the stride cycle proceeds clockwise.
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Fig. 4. Stride frequency, stride length, breath frequency and tidal volume
versus speed for Terrapene carolina (N=54 locomotor
bouts from one individual). (A) Stride frequency (open circles;
y=6.47x+0.3, r2=0.79,
P<0.0001) and stride length (filled squares;
y=0.843x+0.017, r2=0.851,
P<0.0001) versus speed. (B) Tidal volume (filled circles;
y=10.9x+0.611, r2=0.08,
P<0.0377) and breath frequency (open squares; y=
-6.36x+1.62, r2=0.19, P<0.001)
versus speed.
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Fig. 5. Tidal volume (ml breath-1, mean ± S.D.),
breath frequency (breaths min-1) and minute volume (ml
min-1) during 20 min periods of pre-exercise, locomotion, pauses
between locomotor bouts and recovery from exercise in three individual
Terrapene carolina. Tidal volume during locomotion is not
significantly different from tidal volume during pauses or during recovery
(two-way ANOVA, P>0.05). Breath frequency values are not
significantly different between behaviors (paired t-test,
P>0.05). Minute volume during locomotion is significantly higher
than during recovery (paired t-test, P=0.0037).
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Fig. 6. Polar plots of the phase relationship between peak ventilatory airflow and
the locomotor stride cycle for three individual Terrapene carolina
(individual 01, black; individual 02, dark grey; individual 03, light grey).
The stride cycle begins at maximum extension of the left hindlimb (0°) and
continues clockwise around the polar diagram. (A) Timing of peak inhalation
relative to the stride cycle in ten locomotor bouts for each of the three
individuals (inhalations: N=134, 117 and 127 breaths for individuals
01-03, respectively). (B) Timing of peak exhalation (N=132, 117, and
130 breaths for individuals 01-03 respectively). Inhalations from all three
individuals and exhalations from individuals 02 and 03 were randomly
distributed relative to the stride cycle (Raleigh's test of circular
uniformity, P>0.05). Exhalations from individual 01 showed a
statistically significantly non-uniform distribution
(Fig. 6B, black squares;
Raleigh's test of circular uniformity, P<0.001).
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Fig. 7. Polar plots showing the mean magnitude of peak inhalatory and exhalatory
airflow of breaths occurring at different points in the stride cycle for
Terrapene carolina. (A) Individual 01, (B) individual 02 and (C)
individual 03. The magnitude of peak inhalatory (circles) and peak exhalatory
(squares) airflow from the breaths in Fig.
6 were averaged into 20° bins and plotted (means ± 95%
confidence limits) onto the stride cycle. Magnitude of peak airflow increases
with the radius of the plot. The number of breaths varies for each bin (range
0-25) and can be estimated by comparison with the distribution in
Fig. 6. Mean values of peak
airflow rate are considered statistically significantly different (*) if the
95% confidence intervals do not overlap within a bin.
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Fig. 8. Still frames from an X-ray video recording of lung ventilation at rest in
Terrapene carolina (individual 03). Simultaneous pneumotachographic
airflow measurements were also recorded and synchronized with the X-ray video
(Fig. 9). The lungs appear as a
large light area in the middle of the body, and the pneumotach mask appears
dark in this radio-positive lateral view. A small metal marker (arrow) has
been glued to the skin of the inguinal flank just superficial to the oblique
abdominis (OA) and transverse abdominis (TA) muscles. The upper frame shows
the position of the metal marker when the animal has fully inflated lungs. The
lower frame shows the metal marker at the end of exhalation. X-ray video clips
with simultaneous pneumotachographic airflow recordings of Terrapene
carolina breathing at rest and during locomotion can be viewed on line as
part of this article
(http://jeb.biologists.org/).
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Fig. 9. Ventilatory airflow and inguinal flank displacement in Terrapene
carolina (individual 03) during breathing at rest. The upper trace shows
five exhalation/inhalation cycles separated by short periods of apnea. The
lower trace shows vertical displacement ( y coordinate) of a
marker glued to the skin of the inguinal flank just superficial to the oblique
abdominis and transverse abdominis muscles measured from X-ray video
recordings (see Fig. 8).
Exhalation (Ex) occurs as the inguinal flank moves dorsally. Inhalation (In)
occurs as the inguinal flank moves ventrally.
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© The Company of Biologists Ltd 2003
