Effects of Body Mass, Feeding, and Circadian Cycles on Metabolism in the Lizard Sceloporus occidentalis
John H. Roe1,2, William A. Hopkins1,3,
and Larry G. Talent4
1University of Georiga, Savannah River Ecology Laboratory,
Aiken, South Carolina 29802, USA
4Oklahoma State University, Stillwater, Oklahoma, 74078 USA;
Email; talentl@okstate.edu
Abstract
We examined aspects of pre- and postprandial metabolism in the diurnally
active Western Fence Lizard, Sceloporus occidentalis, by measuring
rates of oxygen consumption (Vo2) and carbon dioxide production
(Vco2) at 30°C. Sceloporus occidentalis exhibited
strong circadian variation in metabolism that continued throughout digestion,
with diurnal peaks in metabolism up to four times as high as nocturnal
minimum values (standard metabolic rate, SMR). Metabolism increased with
increasing body size (mass range = 3.65–19.02 g), with mass exponents
ranging from 0.61–0.82. Metabolism of lizards fed meals equivalent
to 1.4, 2.9, and 3.9% of their body mass was elevated above fasting metabolism,
although significant differences in metabolism were not detected among
the three meal sizes. Maximum metabolism during digestion was from 1.2–1.3
times that of maximum fasting metabolism, a value similar to that of other
small, frequently feeding lizards. Specific dynamic action (SDA) ranged
from 2.38–22.02 mL O2 and 1.54–14.54 mL CO2,
or 0.05 -0.44 kJ, which is equivalent to 9.4–17.0% of the ingested
energy. Mean respiratory quotients (RQ) ranged from 0.65–0.68, indicating
lipids were the primary energy substrate used during both fasting and
digestion.
2Corresponding
Author. Present address: Applied Ecology Research Group, University of
Canberra, Canberra, Australian Capitol Territory 2601, Australia; E-mail:
roe@aerg.canberra.edu.au
3E-mail: hopkins@srel.edu
SREL Reprint #2927
Roe, J. H., W. A. Hopkins, L. G. Talent. 2005. Effects of Body Mass, Feeding, and Circadian Cycles on Metabolism in the Lizard Sceloporus occidentalis. Journal of Herpetology 39: 595-603.
