AMER. ZOOL., 19:345-356 (1979).
Amphibian Temperature Regulation Studies in the Field and Laboratory
BAYARD H. BRATTSTROM
Department of Biology, California State University, Fullerton, California, 92634
SYNOPSIS. Studies on thermoregulation in the laboratory and field have come a long way
from the early work done between 1940 and 1960. While some physiological studies on
amphibians have progressed at the same rate as those on reptiles, field studies have been far
behind. Laboratory studies have largely delt with thermal acclimation, evaporative water
loss, and thermal and moisture gradient behavior. Field studies, following early summaries
of body temperatures of field animals, have stressed behavioral thermoregulation; yet,
detailed studies on behavioral thermoregulation in amphibians have been completed for
only a handful of species. A few studies have placed behavioral and physiological thermoregulation into an ecological or energetic framework; these studies are reviewed, and
suggestions are made for future work.
INTRODUCTION
The study of temperature regulation in
amphibians is complicated by the requirement of amphibians to maintain a moist
skin or to occur in an aquatic environment.
Numerous studies have dealt with problems of amphibians in maintaining body
water, avoiding dehydration and adaptations of anurans to the desert (Seymour and
Lee, 1974; McClanahan, 1975; Shoemaker
and McClanahan, 1975). While these
studies have been concerned with water
conservation, they are intimately tied to
problems of temperature regulation. In an
amphibian involved in avoiding dehydration, these responses may take precedence over thermoregulatory ones (Tracy,
1975). Thermoregulation may be compromised by demands of hydroregulation,
while in other situations, thermoregulatory
demands may predominate.
The amphibian's integument also functions in osmoregulation and respiration
(Houston, 1971; Wakeman and Ultsch,
1975; Mullen and Alvarado, 1976; Walters
and Greenwald, 1977). These processes
are, of course, intimately tied to the problems of osmo- and thermoregulation
(Reves, 1977). While I argued some years
back, "Pity the poor frog, nobody studies
his physiology," I would now suggest that
the situation, "Pity the poor frog, his behavioral and physiological problems are so
complicated and interrelated, it is amazing
that we can understand them and that he is
alive at all!!" Since I have recently reviewed
temperature regulation in amphibians
(Brattstrom, 1970a), I propose here to update the field to expose some problems in
our approach, and to suggest some directions for future research.
BEHAVIORAL THERMOREGULATION IN THE FIELD
In a review of body temperatures of amphibians, I confirmed the old notion that
many amphibians are poor thermoregulators (Brattstrom, 1963). For many of
these species, water conservation, or restriction to aquatic environments, forces
I thank Dr. W. W. Reynolds for organizing, and
inviting me to this symposium. Page charges for publi- them into an essentially non-thermoregucation of this paper were supported by N.S.F. grant latpry mode (Fig. 1). The best some aquatic
No. PCM-78-05691 to W. W. Reynolds. The figures amphibians may be able to do is to seek out
were prepared by Mark Zolle supported by a grant warmer or cooler portions of their environfrom the Department of Biology, California State Uni- ment. This thermoregulation behavior
versity, Fullerton. I wish to thank Mark for his drawing
and W. W. Reynolds, Victor Hutchison, and Lon may push them into environments which
McClanahan for comments and remarks on the man- conflict with their respiratory and osmouscript.
regulatory demands {e.g., a warm area of a
345
346
BAYARD H. BRATTSTROM
pond that is low in oxygen) (Houston, 1971; Tracy (1976) suggests that such basking
Wakeman and Ultsch, 1975; Mullen and plays less of a role in the behavioral therAlvarado, 1976; Reves, 1977; Shoemaker moregulation of adult Rana pipiens and that
behavioral thermoregulation in this species
and Nagy, 1977).
Many other amphibians, however, have is poor; and his field data and computer
been shown to be fairly active thermo- simulations indicate that the body temperregulators, interplaying water economy atures of this species are always near amand thermoregulation to allow them to be bient. Evaporative water loss is apparently
more active longer. This presumably allows too high for effective basking thermoregutime for more feeding, reproduction, and lation especially at high radiant levels, low
growth (Lillywhiteetal., 1973). In my initial relative humidities, high air temperatures,
review of amphibian body temperatures, I and high wind speeds. Tracy (1975) also
presented data on several species of frogs showed that a bullfrog, Rana catesbeiana,
(especially Rana cascadae, pipiens, and placed in the sun in a cage, maintained its
clamitans) observed basking in the sun (Fig. body temperature within 4°C. He argues
1), in water or on moist soil (Brattstrom, that this was not thermoregulation as the
1963). These frogs behaved like typical frog was passive and not shuttling (as it
heliothermic lizards, with body tempera- couldn't do). But, he noted, by noon it betures above ambient. The frogs were ap- came dehydrated and stopped producing
parently utilizing evaporative water loss to urine. I suggest that perhaps the frog was
maintain body temperatures below lethal maintaining its body temperature fairly
levels. Later, Lillywhite (1970, 197 la, 1974) constant by physiological thermoregulation
who monitored body temperatures by (evaporative cooling), as it was restrained
telemetry, demonstrated behavioral ther- from doing any behavioral thermoregulamoregulation in Rana catesbeiana which in- tion.
cluded diurnal basking complete with posBasking has only been reported for a few
turing. Brattstrom (1970a) demonstrated other amphibian species. Valdivieso and
that the basking Australian hylid frog, Tamsitt(1974) showed that the montane
Hyla(=Litoria) caerulea, could maintain a Colombian frog, Hyla labialis, is a therfairly constant body temperature by mophilic heliotherm whose body temperevaporative cooling under forced basking, atures are usually higher than ambient due
even when the heat load was increased. The to basking or absorbing solar radiation that
frog apparently could regulate the amount filters through clouds. Adults and subof water passing through its skin, as a func- adults were active in the morning and early
tion of heat load. Another Australian hylid, afternoon. Terrestrial juveniles were active
Hyla Moris, could not do this. Basking anu- at all hours, but were most active at night.
rans use a variety of mechanisms (skin This is in contrast to observations on toads
sculpturing, water movements over the (Seymour, 1972; Lillywhite et al., 1973) in
skin, mucous secretions, activity, and cra- which the juveniles often have higher body
nial co-ossification) to reduce or facilitate temperatures than adults, and spend conevaporative water loss and cutaneous gas siderable time basking. Seymour (1972)
exchange during thermoregulatory bask- suggests that the young of the desert toad,
ing (Lillywhite, 19716; Heatwole and Bufo debilis, utilize basking thermoregulaNewby, 1972; Christensen, 1974; Lil- tion for rapid feeding, accelerated digeslywhite and Licht, 1974, 1975; Sievertetal., tion, and rapid deposition of fat prior to
1974). Lillywhite (1975) showed the im- winter dormancy. Lillywhite et al. (1973)
portant role of blood circulation in main- showed that youngB. boreas basked, except
taining levels of skin hydration during when food was withheld. Orientation to a
basking. As long as water can enter the frog heat source could be elicited in starving
and be effectively evaporated from the skin animals by feeding them, suggesting that
(thus precluding desiccation), many anu- one advantage of such behavior is accelerarans, especially Rana catesbeiana, can main- tion of the digestive processes. Growth
tain fairly constant body temperatures. studies at a variety of temperatures indi-
AMPHIBIAN THERMOREGULATION
347
cated that energy ingestion, linear growth, tion of lipids onto the integument is folweight increase and gross conversion lowed by a complex wiping movement
efficiencies were all maximal at 27°C and which spreads the secretion over the body
were nearly identical to that of toads al- of the frog. The frogs then remain molowed to thermoregulate in a photothermal tionless. This lipid material reduces evapgradient (25.6°). Diurnal behavior of small orative water loss up to 30°C, above which
toads and of tadpoles, compared with the evaporative water loss begins to increase
more nocturnal adults, may have evolved to and then increases precipitously between
maximize growth rates of younger indi- 35 and 40°C. At 40° ambient temperviduals, shortening the time to adult size atures, skin and core temperatures of the
(Brattstrom and Warren, 1953; Brattstrom, frogs remained at 36-37°C. Small increases in water loss resulted in depres1962).
While Bufo boreas, and most amphibians, sions of surface temperature correspondbask only on wet soil, Lilly white et al., ing to the release of clear fluid onto the
(1973) observed some toads basking on dry skin surface (McClanahan et al., 1978).
soil. Perhaps the water storage ability of B. This frog thus uses a skin-surface-protecboreas allows it to bask on dry soil, and then tive device to reduce water loss while living
move to wet soil or water to replenish in the desert, yet as ambient temperatures
rise and the possibility of thermal death
water loss.
the protective nature of this
approaches,
Several species of Australian hylid and
leptodactylid frogs bask (Johnson, 1970, substance breaks down and the skin beI97la,b). These include montane rapid- comes available for evaporative cooling to
stream-dwelling frogs, diurnal tropical maintain body temperatures below lethal
frogs, and semi-desert diurnal and noc- levels.
turnal frogs. The diversity of frogs that
utilize basking suggests that it may occur in BEHAVIORAL THERMOREGULATION STUDIES IN
different species for different reasons and
THE LABORATORY
that the mechanisms of reducing the problems of dehydration and cutaneous gaseStudies on behavioral thermoregulation
ous exchange may be different. Seymour of adult amphibians in the laboratory have
and Lee (1974) have suggested that such been concerned largely with the role of
xeric Australian frogs as Hyla(=Litoria) ru- evaporative water loss and the behavior of
bella and caerulea may solve water and ther- amphibians in thermal gradients. Thermal
moregulatory problems by excreting ur- gradients are difficult to set up for amates, as in other xeric frogs (Loveridge, phibians because of the necessity to avoid
1970; McClanahan, 1975; Shoemaker and dehydration to the animals. It is also
McClanahan, 1973; Shoemaker and difficult to determine whether an animal is
McClanahan, 1975; Blaylock et al., 1976; responding to a thermal or a moisture
Drewes et al., 1977).
gradient. Spotila (1972) in a study of
The tacky and moist-looking skin of plethodontid salamanders in thermal and
many hylid frogs from different deserts relative-humidity gradients, comparing
(such as H. caerulea from Australia, Phyl- gradient studies with field studies, indilomedusa spp. in the New World) elicits cated that these salamanders do avoid exspeculation as to its function. The ar- tremes and exhibit thermal preferenda,
boreal, desert-dwelling Argentinian P. which .were species-specific and not signifisauvagei, not only has utilized certain as- cantly affected by acclimation temperature
pects of nitrogen excretion and osmoreg- or photoperiod. Dehydration was greater
ulation to survive in the desert (Shoemaker at higher temperatures, and in apparent
and McClanahan, 1975), but also uses compensation, the salamanders selected
evaporative cooling in a subtle manner. the highest relative humidity in the graThe skin of this frog is hydrophobic and dient (Spotila, 1972). Thus, the salamancontains numerous alveolar glands con- ders seem to be interplaying thermal and
taining lipids (Blaylock et al., 1976). Secre- moisture responses.
348
BAYARD H. BRATTSTROM
Feder and Pough (1975) studied temperature selection in red-backed salamanders, Plethodon cinereus. Animals acclimated
to low temperatures selected high temperatures in the gradient, and those acclimated to high temperatures selected lower
temperatures; acclimation of temperature
selection was faster than acclimation of
critical thermal maxima. This suggests that
after exposure to, for example, low temperatures, there is value or at least a behavioral response of a salamander to seek
warmer areas. This would facilitate rapid
feeding and digestion following a period
of cold weather and possible starvation.
Hutchison and Hill (1978) showed that
preferred temperatures of bullfrog (R.
catesbeiana) tadpoles varies in a complicated
manner with stage of development and
thermal acclimation. While the mean T b
was 20.7 and the modal T b 21.0°C, there
was a tendency for earlier stages, acclimated at lower temperatures, to select
lower preferred temperatures. At later
stages, and especially with tadpoles acclimated to high temperatures, there was a
preference for higher temperatures. This
latter response may be associated with the
high temperatures selected near metamorphosis, and high temperatures tolerated by recently metamorphosed juveniles.
Hutchison and Hill (1978) further suggest
that for those species with plasticity of their
preferred temperatures, with changes in
acclimation temperatures, survival is enhanced by avoidance of lethal temperatures, and energetic efficiencies are maximized through maintenance of body temperatures at or near physiological and biochemical optima. Plasticity is thus one
strategy for circumventing serious consequences of rapid temperature change or
thermokinetic extremes.
One problem with thermal gradients
constructed for aquatic organisms is vertical thermal stratification. Reynolds and
Casterlin (1976), Reynolds (1977) and
Casterlin and Reynolds (1977, 1978) have
solved this problem by use of a device
which allows an animal to control water
temperature. The animal controls its own
body temperature by its movements between chambers of water monitored by
photocells and associated circuitry which
controls heating and cooling equipment.
Thus by its own behavior an animal can
seek out its preferred temperature by
manipulating the temperature of the water
until it reaches its preferendum. In a study
of R. pipiens tadpoles, Casterlin and
Reynolds (1978) showed that while the
tadpoles had a bimodal aspect of temperature regulation (with highs during day
and again at night and lows during dusk
transitions), the preferred temperatures
and modal preferenda were between 27
and 28°C. These data are similar to results
from typical thermal gradients (Lucas and
Reynolds, 1976) and adult modal field
body temperatures (Brattstrom, 1963). It
seems to me that the development of effective thermal gradients or use of shuttleboxes will provide an opportunity for critical studies on the roles of photoperiod,
acclimation, and energy metabolism on behavioral thermoregulation. The shuttlebox
device (Reynolds, 1977) also may be adaptable to studying simultaneous responses to
several factors (i.e.., choices between high
temperature-high oxygen water vs. high
temperature-low oxygen water against a
choice of low temperatures and different
oxygen levels).
Some of the studies of Lilly white et al.
(1973) on B. boreas juveniles were carried
out in a laboratory photothermal gradient.
Behavior of these toadlets differed under
different soil and starvation conditions.
Since it is also clear that acclimation and
photoperiod may affect some amphibians,
it may be important to mention here that
length of time that animals are exposed to
the gradient (number of hours or days in
the gradient), the number of animals used
at any one time, acclimation influences,
gradient size, shape, and thermal consistency, and desiccation levels may also affect
responses of animals to a gradient, so caution should be taken in construction, experimental design, and data interpretation
of thermal gradient studies.
PHYSIOLOGICAL THERMOREGULATION STUDIES
IN THE LABORATORY
Most laboratory studies on amphibians
AMPHIBIAN THERMOREGULATION
haye dealt with physiological aspects other
than thermoregulation. Considering the
kinds of studies that have been done on
reptiles, it is surprising to find so few
studies on amphibian thermoregulation.
In heating and cooling studies on the
bullfrog,/?, catesbeiana, (Tripp and Lustick,
1974) in water and air, there was no difference in heating and cooling of frogs in
water, but there was in air. Heart rates
were higher during heating than during
cooling in water, while there was no difference in heart rates during heating and
cooling in air.
The majority of physiological studies in
amphibians have understandably been
metabolic studies on the relationship of
metabolism to gas exchange, surface area,
and habitat. Most of these studies were
done at a variety of temperatures, and thus
contribute to our understanding of the
physiology of amphibians and the relative
importance of behavioral and physiological thermoregulation to enhance or curtail
certain aspects of the animals' physiology
(see the following papers for current
physiological and environmental approaches to old problems; Clausen, 1973;
Bennett and Wake, 1974; Guttman, 1974;
Turney and Hutchison, 1974; Heath,
1976; Pitkin, 1977; Weathers and Snyder,
1977). In addition, the interplay between
these responses sometimes provides solutions to, or problems for, other physiological responses of the animal.
Recent studies have made us aware of
the increasing importance of the role of
anaerobic respiration in stress activity and
in normal behavior. Guttman (1974), for
example, has shown that the toad, B. valliceps, can stand anoxia longer than B.
woodhousei. He suggests that this allows B.
valhceps to endure its longer winter dormancy better than B. woodhousei (also see
Armentrout and Rose, 1971). Turney and
Hutchison (1974) have shown in R. pipiens
that of stressed energy, 69 and 73% was
supported anaerobically at 25° and at 15°C,
respectively. They suggest that the inefficiency of the breathing cycle of this frog,
coupled with limitations of the respiratory
surface and separate gas exchange pathways, have placed extreme restrictions on
349
the capacity of the frog to meet oxygen
demands, thus forcing the animal to incur
a relatively large oxygen debt during
maximal activity. Other studies with anaerobic respiration (Bennett and Licht,
1973, 1974; Seymour, 1973; Bennett,
1978) suggest that slow-moving amphibians such as B. boreas produce small
amounts of lactate and do not exhaust. In
contrast, fast-moving jumping forms such
as R. pipiens have high levels of lactate generation, but are unable to sustain maximal
activity. Aquatic species rely largely on
air-gulping during activity and show little
anaerobiosis. The rate of lactate production is also directly correlated with predatory avoidance. Noxious-tasting, aggressive, or cryptically-colored amphibians
have low anaerobic scopes for activity while
others rely upon anaerobiosis for rapid
flight (R. pipiens) or rapid avoidance behavior {Batrachoceps attenuatus). In fact,
rapid activity in amphibians appears to be
possible only at the expense of extensive
anaerobiosis (Bennett, 1978). In my opinion, two important lines of research are
developing from these studies. First, is the
question of how the enzymes and enzymatic pathways that are involved in aerobic
and anaerobic respiration (Bennett, 1974,
1978; Baldwin et al., 1977) respond to the
thermoregulatory demands of the animal
and whether the same enzymes and pathways are used at all temperatures.
Many organisms, including amphibians,
compensate aspects of their metabolism so
that they are more efficient at specific temperatures than would be predicted otherwise. The studies on such compensation
mechanisms in amphibians have largely
been restricted to adaptations by amphibian larvae, especially in embryonic temperature adaptations in northern and alpine
frogs (Licht, 1971; McLaren and Cooley,
1972; Packard, 1972; Brown, 1975; Kuramoto, 1975a,b). A perhaps equally important aspect of metabolic compensation is that shown by high elevation populations of adult salamanders (Fitzpatrick and
Brown, 1975) and anurans (Packard and
Bahr, 1969; Packard, 1971, 1972) though
in recent studies on Pseudacris triseriata, the
compensation may not be in oxygen con-
350
BAYARD H. BRATTSTROM
sumption but in differences in breeding
seasons, and activity times (Packard, 1971).
A considerable body of literature on amphibian physiology has been concerned
with thermal resistances and the effect of
thermal histories on thermal tolerances.
Studies on the rate and range of thermal
acclimation have provided us with information on the physiological plasticity of
amphibians, and on genetic limits on thermal tolerances. These data have also been
shown to have zoogeographic implication
(see reviews in Brattstrom, 1970a, b). Recent studies have extended these ideas {e.g.,
Pough and Wilson, 1970; Farrell, 1971;
Fitzpatrick et al., 1971; Holzman and
McManus, 1973; Pough, 1974; Burke and
Pough, 1976; Feder, 1978; Hoppe, 1978).
Importantly, others are looking at acclimation effects on tissues (Shertzer etal., 1975;
Lascano et al., 1976; Lagerspetz, I977a,b;
Ballantyne and George, 1978) and blood
parameters (Weathers, 1975, 1976). Interestingly, Ballantyne and George (1978)
have shown that acclimation to cold (from
21 to 5°C over one month) in R. pipiens can
raise muscle mitochondrial content.
Whether this is an adaptation for dormancy
is unknown, but worthy of continued study.
These studies hopefully will contribute to
our understanding of the physiology of the
amphibian in solving its simultaneous
problems of temperature, water, gas, and
ionic regulation (Fig. 1). They are already
giving us a clue to the basis for the marked
seasonal differences seen in some amphibians. Lagerspetz, (19776), for example has
shown that there is a temperature and seasonal effect on CNS activity mediated by the
thyroid via the autonomic nerves. These
seasonal differences may be important for
spring reproductive effort and winter survival.
moregulation involves monitoring behavior at the same time as body temperature (i.e.., watching for emergence, and
then recording body temperature of
emerging animals). Of all the field body
temperatures recorded (Brattstrom, 1963,
1970a; Lillywhite et al., 1973), behavioral
thermoregulation was sufficiently documented for only a few species (B. boreas,
Acris crepitans, H. regilla, R. catesbeiana,
Taricha rivularis). A more effective way to
study this type of thermoregulation is by
the use of telemetry. Lillywhite (1970,
1971a, 1974, 1975) has used this and other
techniques to effectively study behavioral
thermoregulation in the field and the lab.
While body temperature is a function of
environmental inputs and of physiological
responses and interactions, in these studies
body temperature was usually the only
physiological parameter measured. It is
important to measure several physiological
parameters of amphibians simultaneously
with modified technology and with patience.
One area of field investigations not yet
touched with amphibians is the construction of time/activity budgets in the field.
This will be an essential step in the construction of time/activity/energy budgets
and in appreciating the role played by amphibians in total community energy budget.
This will be a difficult task due to the secretiveness and nocturnality of many amphibians and will require patience since many
amphibians spend a lot of time being inactive. Yet, this may be an important part of
energy conservation in amphibians.
ENERGY METABOLISM AND ENERGY BUDGETS
PHYSIOLOGICAL STUDIES ON TEMPERATURE
REGULATION IN THE FIELD
Considerable interest has developed recently on the relative roles of energy production in amphibians (Hutchison et al.,
1977; Bennett, 1978). We now have studies
on energy metabolism in amphibians involving size, season, fat deposition and
Body temperatures taken of amphibians in the field are important, but this is
not studying thermoregulation. As pointed out by Heath (1964, 1965) these data
describe only the limits and possible preferenda of the animals. Studying ther-
FIG. 1. Diagrams of body-environment interactions
of three types of amphibians. Above, a basking
(heliothermic) anuran (partly after Pough, 1974;
Tracy, 1975, 1976). Middle, a cryptic salamander or
largely nocturnal anuran. Below, an aquatic amphibian; (larval or adult).
>
AMPHIBIAN THERMOREGULATION
351
DIURNAL AND
BASKING AMPHIBIAN
'particular
CONVECTIVE
HEAT LOSS
THERMAL RADIATION
FROM ATMOSPHERE
SCATTERED AND
REFLECTED SUNLIGHT
WATER
LOSS
THERMAL RADIATION
TO ENVIRONMENT
THERMAL RADIATION
FROM VEGETATION
EVAPORATIVE
HEAT LOSS
THERMAL RADIATION
FROM GROUND
HEAT CONDUCTION
TO OR FROM GROUND
WATER INPUT
FROM SOIL
SECRETIVE OR
NOCTURNAL AMPHIBIAN
CONVECTIVE HEAT
GAIN AND LOSS
EVAPORATIVE
HEAT LOSS
THERMAL RADIATION
TO ENVIRONMENT
GASEOUS
EXCHANGE
WATER INPUT
FROM SOIL
GASEOUS
EXCHANGE
HEAT CONDUCTION
TO OR FROM GROUND
AQUATIC
AMPHIBIAN
BEHAVIORAL RE8PONSE
TO AND FROM
WARM WATER
GASEOUS
EXCHANGE
CONVECTIVE AND
CONDUCTIVE HEAT
TO AND FROM WATER
352
BAYARD H. BRATTSTROM
utilization, and reproductive effort (Seymour, 1973; Seymour and Lee, 1974; Fitzpatrick and Atebara, 1974; Beckenback,
1975; Tracy, 1975, 1976; Feder, 1976). Recent studies on feeding behavior and digestion efficiencies have also contributed to
our understanding of the energy utilization
of amphibians (Lillywhite et al., 1973;
Sternthal, 1974; Tracy, 1975; Smith, 1976).
Fitzpatrick (1973) has studied energy
budgets in the salamander Eurycea bislineata, and Smith (1976) has produced an
energy budget (Fig. 2) for the toad/?, terrestris. Assuming a digestive assimilation efficiency of 74%, about half of that energy
goes into metabolic costs and half into
production. Of the latter, about half goes
into growth and half into reproductive effort (Fig. 2). The latter, of course, may be
variously partitioned at different ages and
seasons.
Burton and Likens (1975) have determined that the energy flow through the
salamander population in a New Hampshire forest is 11,000 KCal/ha/yr, equal to
0.02% of the net primary productivity and
about 20% of the energy flow through
birds and mammals in the forest. On the
other hand, salamanders are 60% efficient
in converting ingested energy into new tissue, and produce more new tissue annually
than do bird populations. If we had some
time/activity budgets for more amphibians, we could begin to develop time/activ-
ENVIRONMENT = 100 °70
INGESTION
26°7C
UNASSIMILATED
ENERGY
74°7 C
ASSIMILATED
ENERGY
38°7 O
36°7 O
METABOLIC
COSTS
o°r.
PRODUCTION
OF TISSUES
O-36°7o|
GROWTH
3O.6°7O f
LEAN DRY
BIOMASS
I O - 3 6 °7 O
REPRODUCTION
54°7 n
FAT
ACCUMULATION
FIG. 2. An energy budget for the toad, Buju ttrre\ln\ (modified after Smith, 1976).
353
AMPHIBIAN THERMOREGULATION
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LIVER
• •
BLOOD GLUCOSE
^—
LIVER LIPIDS
FAT BODIES
GLYCOGEN
II
It
>
O
3
I<
EMERGENCE
1
1
1 »
/
1 t
/
1 1
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1
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1
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1
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,
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ity/energy budgets and begin to approach
the problem of the cost of thermoregulation.
While many workers have noted seasonal
changes in "winter" and "summer" frogs
(Brattstrom, 1970a), it has only been in light
of renewed interest in energetics that new
approaches to seasonal changes in metabolism have been made (Fitzpatrick, 1971;
Harri, 1973; Harri and Talo, 1975a,b;
Shertzer, et al., 1975; Weathers, 1975,
1976; Lagerspetz, 1977a,6). In terms of energy metabolism, and thus the costs for a
variety of functions, it is also important to
know how an amphibian may be partitioning the utilization of its energy with season.
Thus Lillywhite et al. (1973) suggest that
behavioral thermoregulation and energy
partitioning in juvenile toads (B. boreas)
maximize growth, and shorten the time to
reach adult size. This is also apparently true
for B. terrestris (Smith, 1976). In adults, energy is largely partitioned into reproductive
effort (production of eggs and sperm, and
cost of reproductive behavior). In addition,
amphibians must also prepare for cold
winters or long periods of dormancy underground (Seymour, 1973). Seasonal differences in metabolism of adult amphibians
probably represent an interplay between
energy utilization for reproduction and
preparation for winter. Recent studies
(Pasanen and Koskela, 1974; Koskela and
Pasanen, 1975; Byrne and White, 1975)
have demonstrated marked and interesting
changes in liver and muscle glycogen, blood
glucose, and body lipids. In R. catesbeiana
lipid reserves become exhausted from the
time of emergence through the breeding
season (Byrne and White, 1975). Lipid reserves then increase prior to and into dormancy, while blood glucose levels rise during the breeding season and are lowest
upon emergence from dormancy (Fig. 3).
These may not be the same kind of changes
seen in other amphibians (Reno etal., 1972;
Seymour, 1973; Gehlbach etal., 1973), but
the physiological strategies used are probably a function of the different seasonal activities employed by different amphibians.
Depressed metabolism, fat deposition and
utilization, and ability to endure anoxia (or
have low oxygen demands) probably allow
• • *
.'
BREEDING
«./-'"
DORMANCY
FIG. 3. Seasonal changes in lipid reserves, and blood
glucose levels in the bullfrog, Rana catesbeiana (Simplified after Byrne and White, 1975).
amphibians to survive harsh periods. At
this time, thermoregulation and its costs are
probably low. The costs and benefits of
thermoregulation are highest during seasonal activity and help in growth, energy
metabolism, and reproductive effort. Much
more needs to be done; modeling efforts
(Tracy, 1975) may be an important next
step.
SPECIAL ASPECTS AND PROBLEMS
Some anurans prefer temperatures exceeding 30°C (e.g., H. Smithi, rubella, Phyllomedusa sauvagei; Brattstrom, 1970a,b;
Johnson, 1970, 1971a,6; Seymour and Lee,
1974; McClanahan «£«/., 1978). Interesting
physiological processes may occur in frogs
at high temperatures, (Stephenson, 1967;
Harri and Talo, I975a,b) implying the necessity of measurements at >30°C.
Kluger (1977) demonstrated that H.
cinerea developed a fever (increase of 2°C.in
body temperature) following injections of
killed Gram-negative bacteria (Aeromonas
hydrophila). Casterlin and Reynolds (1977)
demonstrated a similar "behavioral fever"
(significant mean increases in preferred
temperature) in tadpoles of R. catesbeiana
and R. pipiens, following similar injections
with the same bacteria. These studies have
implications both for understanding the
354
BAYARD H. BRATTSTROM
adaptive advantage of fever in diseased
frogs, and as a means of studying hypothalamic control of thermoregulation.
I think we need a new look at the endocrinology of amphibians with respect to
metabolism, energy demands and seasonal
activities. This is especially true now that we
know that season and temperature affect
nervous and endocrine system activities
(Lagerspetz, 1977<z, b).
I have said little about thermoregulation
in tropical amphibians, largely due to the
dearth of studies. Tropical amphibians may
be different. Selection pressures in the
tropics may place higher demands on social
behavior and reproductive modes than on
physiology.
(ed.), Comparative physiology of thermoregulation, pp.
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Byrne, J. J. and R. J. White. 1975. Cyclic changes in
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