Saddleback Journal of Biology - Saddleback College

Fall 2009 Biology 3B Paper
arterial pressure, an increased heart rate will occur
and produce a heightened metabolic rate (MR).
Although oxygen saturation of the tissues in the body
decreases with a sudden decrease in the partial
pressure of oxygen (Beall 2001), it will eventually
increase with time as adaptation occurs. The
descriptions of these adaptations give a broad idea of
how a body can compensate for the introduction to a
lower partial pressure of oxygen than what was
previously used by an organism. It has also been
noted that some adaptations take longer to acquire
(Angilletta 2000). When there is a sudden
introduction to a lower significantly higher altitude,
the body cannot efficiently adapt immediately, and as
a result, the short term response is an increase in the
rate of oxidation in the citric acid cycle (Raugi et al.
1975). Ultimately, the body must work harder to keep
up the homeostatic processes, especially due to a
sudden depletion in oxygen content without sufficient
time for the body to adjust, which results in an
increase in the metabolic rate.
The researchers conducted this study in
order to examine how the lower concentration partial
pressure will affect the metabolic processes in ten S.
occidentalis which can lead to a better understanding
of how fragile the cellular respiration processes are in
the ectotherms. This study introduced S. occidentalis
to a target altitude about 2000 meters higher (known
as the “Altitude” testing site) than the elevation of the
habitat from which they were collected, and then also
at 3 meters (known as the “Sea Level” testing site).
Twenty-one percent of the atmosphere at sea level (0
meters) is made up of oxygen. However, to simplify
the comparisons in this study, the oxygen partial
pressure at 0 meters has been standardized to 100%,
which will allow for less complicated deductions.
Also, the study focused upon the standard metabolic
rate (SMR) for S. occidentalis due to the use of fasted
and calm disposition of the ectotherms. The
investigators hypothesized that with these specific
altitudinal changes, there would be a significant
increase in the SMR of S. occidentalis at the 2,194
meter testing site.
Materials and Methods
Sceloporus occidentalis were first collected
from the Orange county area over a two week period
during October of 2009. A total of ten lizards, five
males and five females, were collected at an altitude
of 186 meters and were housed in a glass aquarium
and fed a steady diet of crickets. The lizards were
fasted for a period of 24 hours after which they were
weighed. The males weighed 11.27 ± 3.09 g (MEAN
± SE, n = 5) and the females were 11.39 ± 1.52 g
(MEAN ± SE, n = 5). After weighing, the lizards
were then taken to Fawnskin, California, at an
altitude of 2,194 meters. The pressure was measured
at 591 mmHg using a barometer set up with the
Pasco GLX unit, and the altitude was recorded using
a Garmin GPS. The temperature was recorded at
21.3°C using a temperature probe also on the GLX
unit. One specimen at a time was placed into a 500
milliliter container with a CO 2 probe linking the
container to a GLX unit. The lizard was placed into a
dark covered area and allowed a five-minute
adjustment period for anxiety to subside. During this
time and also during the actual testing period, noise
and disruptions were kept to a minimum to help
ensure the specimen stayed calm. After five minutes,
the containers were sealed with only the probe
connecting the container to the GLX unit and data
was collected for a period of 300 seconds. The lizards
were faced away from the probe to prevent CO 2 from
being exhaled directly into the device. This procedure
was repeated for all ten lizards and data was recorded
to a USB flash drive to be later converted to mL CO 2
· g -1 · hr -1 . The lizards where allowed a two-day rest
period, again fasted for 24 hours, and were then
brought down to Aliso Creek Beach in Laguna
Beach, California, at an altitude of 3 meters where
the procedure that was performed at Altitude was
repeated at Sea Level. The temperature at Sea Level
was recorded at 20.9°C and barometric pressure was
760 mmHg. The data collected from both testing
sites were then downloaded to Data Studios and
calculations were made. In order to use the CO 2
produced by the lizards to determine their standard
metabolic rate (SMR), the following equation was
used:
SMR =
Slope
Sec
60 sec 60 min 1
x x x
. min hr wt .
The CO 2 produced by each lizard was taken
in units of ppm/sec and was converted to mL/L. The
weight of the lizards was taken in grams, and the
volume of the container the lizards were housed in
while testing was 0.500 liters. The lizards SMRs
were found and then the mean was calculated for the
Sea Level and Altitude SMRs. A paired, one-tailed t-
test was run on the data using Microsoft Office
Excel.
Results
During exposure to the 33% lower oxygen
partial pressure levels at Altitude than those at Sea
Level, the mean SMR obtained was not significantly
different to the mean SMR calculated at Sea Level.
The mean SMR for S. occidentalis at 3
meters was 0.1922 ± 0.02152 mL CO 2 ·• g -1 ·• hr -1 (±
SEM, n = 10) (Figure 1). The lizards mean SMR at
2,194 meters was 0.1994 ± 0.02007 mL CO 2 ·• g -1
•hr -1 (± SEM, n = 10). The average standard
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Saddleback Journal of Biology
Spring 2010