Aerobic Metabolism During Predation by a Boid Snake
Camila Canjani, Denis V. Andrade, Ariovaldo P. Cruz-Neto and Augusto S. Abe
Departamento de Zoologia, UNESP, Rio Claro, SP, 13506-900, Brasil
e-mail: denis@rc.unesp.br
We quantified the oxygen uptake rates (VO2) and time spent, during the constriction, inspection, and ingestion of prey of different relative sizes, by the prey-constricting boid snake Boa constrictor amarali. Time spent in prey constriction varied from 7.6 to 16.3 min, and VO2 during prey constriction increased 6.8-fold above resting values. This was the most energy expensive predation phase but neither time spent nor metabolic rate during this phase were affected by prey size. Similarly, prey size did not affect the VO2 or duration of prey inspection. Prey ingestion time, on the other hand, increased linearly with prey size although VO2 during this phase, which increased 4.9-fold above resting levels, was not affected by prey size. The increase in mechanical difficulty of ingesting larger prey, therefore, was associated with longer ingestion times rather than proportional increases in the level of metabolic effort. The data indicate that prey constriction and ingestion are largely sustained by glycolysis and the intervening phase of prey inspection may allow recovery between the two predatory phases with high metabolic demands. The total amount of energy spent by B. c. amarali to constrict, inspect, and ingest prey of sizes varying from 5 to 40% of snake body mass varied inversely from 0.21 to 0.11% of the energy assimilated from the prey, respectively. Thus, prey size was not limited by the energetic cost of predation. On the contrary, snakes feeding on larger prey were rewarded with larger energetic returns, in accordance with explanations of the evolution of snake feeding specializations.
A bloody meal: The costs of being a vampire bat
A. P.Cruz-Neto1, Thomas H. Kunz2, Augusto S. Abe1, Robert Michener2 & George Camargo3
1 - Depto. de Zoologia, IB, UNESP. CP 199 13506-900, Rio Claro, SP, Brazil.
E-mail: neto@rc.unesp.br
2- Department of Biology, Boston University, Boston, USA
3 – Departamento de Ecologia, Universidade Federal do Mato Grosso,
Brazil.
In vertebrates the use of blood as the solely food is restricted to three species of Neotropical phyllostomid bats. Although the evolutionary steps that leads to this unusual feeding habits is disputable, use of blood as food is associated with the evolution of a unique suite of behavioral, morphological and physiological adaptations. A combination of a peculiar foraging behavior with a diet rich in protein, but with a low energy content, is tough to be correlated with a differentiate pattern of digestive performance, evaporative water loss and thermoregulatory strategy. Laboratory studies suggest that the maintenance of water homeostasis is achieved at the expenses of a reduced thermoregulatory capacity in post-absorptive vampire bats. However, indirect evidence suggest that the low food transit time observed in vampire bats may allow these animals to divert some of the heat generated during the digestion to thermoregulation. For free-ranging vampire bats, preliminary studies indicate that behavioral selection of roosting may ameliorate the physiological costs brought about by its unusual diet. Even so, the costs of being a vampire bat is translated into a low daily energy expenditure and low rates of water turnover in the field (as measured by the double-labeled water method) when compared with bats (or other mammals) with more “usual” diets. These costs, in turn, affect several aspects of the life history of vampire bats, especially those related with reproduction and growth.
Financial Support: FAPESP, NSF.
Tobias Wang, Johannes Overgaard and Johnnie Andersen
Department of Zoophysiology, University of Aarhus, Denmark
Many reptiles and amphibians eat very large meals and habitually undergo
prolonged periods of fasting. The physiological processes associated with
digestion are pronounced and metabolic rate typically increase many-fold;
in some snakes, oxygen uptake during digestion may even exceed that attained
during exercise. In snakes, the postprandial increase in oxygen uptake
is independent of the duration of the preceding fasting period, and the
large metabolic response to feeding does, consequently, not appear to
be caused by upregulation of intestinal mass. Studies on cardiorespiratory
responses to digestion may reveal fundamemtal mechanisms regarding structural
and functional constraints of metabolic rate in ectothermic animals. Net
transfer of HCl to the stomach causes a metabolic alkalosis in blood and
tissue, but in all animals studied so far, the pH changes are reduced
through ventilatory compensations that increase arterial PCO2.
Arterial PO2 does, nevertheless, remain high throughout
digestion. Heart rate and systemic blood flow increase several-fold during
digestion, but do not match the metabolic changes, implying that arterial-venous
extraction increases. In amphibians an increased haematocrit also contributes,
but this does not appear to be the case in reptiles. In snakes and alligators,
however, there are changes in blood oxygen affinity that may play a role
in securing oxygen delivery. The cardiovascular adjustments appear to
involve non-adrenergic-non-cholinergic mechanisms as well as withdrawal
of vagal tone. In this presentation, we compare and contrast the cardiorespiratory
responses to digestion and exercise.
Wang, Busk and Overgaard (Comp. Biochem. Physiol. 128A:335-49).
Supported by the Danish Research Council.
Indigenous browses and diet quality of grazing herbivores in Botswana
A.A. Aganga & U.J.Omphile
University of Botswana, Gaberobe, Botswana
Animal production in Botswana suffers from inadequate feed quantities
and qualities, due mainly to semi-arid low rainfall which can barely support
arable farming in most years. This problem is compounded by the competition
between the livestock and human feed industries for the little available
pulses and cereals. Consequently, tree fodders are available forage resources
which grazing herbivores can utilize without competition from monogastric
animals and man. Indigenous browses are utilized as supplements to low
quality grasses and straws by domestic herbivores. Most tree leaves and
twigs contain tannins, an antinutritional factor for which proper precautions
need to be taken in selecting the species of trees and their level of
feeding to grazing domestic animals.
Wild herbivores depend solely on the rangelands for their feeding and
nutrient requirements.A diet quality study evaluated seasonal effects
on dung ash, N, and P contents of 5 herbivores chosen to reflect the range
of large ungulate herbivory in the Chobe National park. The study evaluated
seasonal dynamics of diet quality of buffalo, elephant, giraffe, impala,
and kudu. To aid in interpreting results of this study, a feeding trial
was also conducted where goats and sheep were fed mixtures of diets of
known ash, nitrogen (N), and phosphorus (P) contents. Goats and sheep,
respectively, represented those wild animals that browsed and those that
grazed in their natural habitats. The field study was a randomized block
design and the feeding trial a 4 X 4 Latin square design using 4 goats,
4 sheep, and diet formulations comprised of 4 shrubs and 1 grass hay.
Average dung ash contents of the 5 herbivores were the same in both years,
but higher in the wet than dry seasons. Dung ash contents also varied
among animals with higher contents in impala and kudu and lower contents
in the elephant and giraffe. The average dung N contents were higher in
the wet than dry seasons of each year. There was no difference in the
dung N contents between years in the dry season. Dung N contents were
highest for giraffe and kudu, intermediate for impala and buffalo, and
lowest for elephant. Dung P contents were also higher in the wet season
than in the dry season, and the rank order of the P contents was: impala
> kudu > giraffe > buffalo > elephant. Buffalo and elephant
consumed diets lower in N and P than impala, giraffe, and kudu; impala
and kudu consumed diets higher in ash than buffalo and elephant. Prediction
of diet ash from dung ash was not a reliable index because dung ash accounted
for only 23% and 12% of the variation in dietary ash contents of goats
and sheep, respectively. Nitrogen contents of the dung, however, was reflective
of the N contents of the diet although the confidence of prediction was
lower in the browse diets than in the grass diets. Dung P contents of
browsers accounted for more than 75% of the variation in diet P contents
and 50% of the variation in the diet P contents of grass diets. Dung N
and P contents were, therefore, better indices of diet N and P contents
than dung ash was for diet ash.
Effects of feeding on the gut morphology, innervation and motility in Burmese python
Anna Holmberg1, Jörgen Jensen1, Tobias Wang2 and Susanne Holmgren1
1University of Göteborg, Department of Zoology/Zoophysiology,
Box 463, SE-405 30 Göteborg, Sweden
2Dept Zoophysiology, University of Aarhus, Denmark
(anna.holmberg@zool.gu.se)
Reptiles and amphibians that feed at infrequent intervals show, in contrast
to frequent feeders, a prominent increase of brush border transport rates
and gastrointestinal mass after feeding. The Burmese python, Python
molurus bivittatus, is such an infrequent feeder that exhibits a large
and rapid increase of metabolism and a two-three fold increase in intestinal
mass by two days after feeding. The increased mass is predominantly caused
by swelling of the individual enetrocytes rather than cell proliferation,
and it was recently suggested these changes are energetically cheap and
that the intestine is structurally flexible but remain functional during
fasting periods (Starck and Beese, J. Exp. Biol., 2001.204.325-335).
However, little is known about the putative changes in the nervous and
humoral control systems of the gut and it is not known whether feeding
affects innervation and motility of the stomach and intestine. By using
immunohistochemistry, we have investigated the possible up/down regulation
of different neurotransmitters in animals that had been fasted for a minimum
of three weeks and animals that had ingested a large meal two days before
the experiments were conducted. We found no major changes in the innervation
by substance P (SP), NKA, galanin, VIP, PACAP, NOS, or somatostatin. Neither
did we find any differences in the effect of SP, galanin, CGRP, VIP, PACAP,
or bradykinin on motility in strip preparations from stomach and intestine.
We conclude that although there are considerable changes in gut thickness
and absorptive properties after feeding, the smooth muscle and its control
appear little affected.