First published online June 16, 2005
Journal of Experimental Biology 208, 2595-2609 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01659
Physiological responses to feeding, fasting and estivation for anurans
Stephen M. Secor
Department of Physiology, University of California at Los Angeles,
School of Medicine, Los Angeles, CA 90095-1751, USA and
*Department of Biological
Sciences, The University of Alabama, Tuscaloosa, AL 35487-0344, USA
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Fig. 1. Light microscopy photographs of the intestinal mucosa prior to (normal) and
after intestinal segments have been everted and incubated for fasted and fed
Bufo marinus and Rana catesbeiana. Also illustrated are
means of villus length of normal non-everted intestinal segments, everted
intestinal segments, and everted intestinal segments that have been incubated
in unstirred and stirred Ringers solution for fasted and fed B.
marinus and R. catesbeiana. Note that villus length is not
altered following everting and incubation. In this and all following figures,
error bars represent ±1 S.E.M. and are omitted if the
S.E.M. is smaller than the width of the symbol for mean value.
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Fig. 2. Mean  O2 at
30°C prior to (day 0) and up to 8 days following the ingestion of rodent
meals 15% of anuran body mass for estivating Bufo alvarius, Ceratophrys
ornata and Pyxicephalus adspersus, and non-estivating Bufo
marinus, Leptodactylus pentadactylus and Rana catesbeiana
(N=6 for each species).
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Fig. 3. Log SMR (A), peak postprandial
O2 (B), and SDA
quantified as kJ (C) plotted against log body mass for estivating Bufo
alvarius, Ceratophrys ornata and Pyxicephalus adspersus and
non-estivating Bufo marinus, Leptodactylus pentadactylus and Rana
catesbeiana. Note the lower SMR and higher SDA of individuals of
estivating species compared to individuals of non-estivating species.
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Fig. 4. Uptake rates of the amino acids L-leucine and
L-proline and of the sugar D-glucose by the anterior (A)
and distal (D) portions of the small intestine for each of six anuran species
after a 2-week fast (fasted, open bars) and at 1 day postfeeding (fed, solid
bars). Note that of the non-estivating species, only Bufo marinus
experienced a postprandial increase in intestinal nutrient uptake (glucose
uptake by the anterior small intestine). In contrast, all three estivating
species experienced significant postprandial increases in the uptake rates of
all three nutrients by the anterior small intestine and in half the cases by
the distal small intestine. In this and subsequent figures, levels of
significance (for change with feeding) are illustrated with asterisks;
*P<0.05, **P<0.01,
***P<0.001.
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Fig. 5. Total intestinal uptake capacity for the amino acids L-leucine
and L-proline and of the sugar D-glucose after a 2 week
fast (fasted, open bars) and at 1 day postfeeding (fed, solid bars) for six
anuran species. Note that the three non-estivating species experienced no
significant postprandial increases in nutrient uptake capacity (with the
exception of D-glucose for Bufo marinus), whereas all
three estivating anuran species significantly upregulated intestinal uptake
capacity of each nutrient with feeding.
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Fig. 6. Mass and length of the small intestine of two-week fasted (fasted, open
bars) and fed (solid bars) anurans of six species. Each of three estivating
species experienced significant postprandial increases in small intestinal
mass and length, whereas only the non-estivating Bufo marinus
experienced an increase in intestinal size.
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Fig. 7. Width of the intestinal serosa and muscularis/mucosa layers, and height,
width and volume of intestinal enterocytes of six anuran species after a 2
week fast (fasted, open bars) and at 1 day postfeeding (fed, closed bars).
Note that none of the six species experienced a significant change in serosa
width, whereas mucosa width increased significantly postfeeding for the three
estivating species. Enterocyte height increased postprandially for only the
two species of bufonids, whereas enterocyte width and volume increased
significant for all six species with feeding (with the exception of enterocyte
volume for Leptodactylus pentadactylus).
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Fig. 8. Mean O2 at
30°C, small intestinal (SI) mass, and total small intestinal uptake
capacity of L-leucine, L-proline and
D-glucose, of Ceratophrys ornata and Pyxicephalus
adspersus either following a 2 week fast (fasted, open bars) or following
1 month of laboratory-induced estivation (estivated, closed bars). Note that
with estivation, both species experienced significant decreases in metabolic
rate, intestinal mass and performance.
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Fig. 9. Electron micrographs of intestinal microvilli of fasted and fed Bufo
marinus and Pyxicephalus adspersus. Note the lack of a
significant postprandial change in microvillus length for either species.
Bars, 1 µm.
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© The Company of Biologists Ltd 2005
