Nonavian Reptiles as Laboratory Animals
Harry W. Greene
INTRODUCTION
The taxon Reptilia encompasses more than 15,000 species of
vertebrates, of which more than 9,000 are birds (de Queiroz
and Gauthier 1994) and not dealt with herein. This leaves
roughly 300 species of turtles, 22 species of crocodilians, 2
species of tuataras, 3,000 species of lizards, 175 species of
amphisbaenians, and 2,700 species of snakes that are linked
by ectothermy and certain other retained primitive characteristics, yet are highly divergent among themselves. In the rest
of this article they are referred to collectively by the traditional term "reptiles." That birds (whose closest relatives are
crocodilians) are reptiles in exactly the same way that primates
are mammals underscores the wide range of morphology,
physiology, and behavior achieved by those evolutionary lineages that even many biologists still anthropocentrically call
"lower vertebrates." This extreme diversity among and within
reptile groups is widely underappreciated yet central to their
welfare in captivity.
This paper briefly reviews issues in the acquisition, maintenance, and use of reptiles in laboratory research. I do not
provide details on the care of a few particular species, because years of experience on an institutional animal care and
use committee (IACUC) convince me that such exemplar
guidelines reinforce a well-meaning but false hope—that we
can manage captive reptiles with the same kind of straightforward, simple, and uniform care afforded laboratory mammals. My strongest message here is that strict general guidelines covering organisms as different as turtles, lizards, and
even different species of snakes are counterproductive—indeed such guidelines could lead to inhumane maintenance.
Instead, proper care of these creatures often requires fairly
specific information on natural history (Greene 1986) and an
open-minded commitment to their welfare.
COMPOSITION, CHARACTERISTICS, AND
USE IN RESEARCH
Beyond the trademark shell, turtles (also known as chelonians) range from strictly terrestrial, dome-bodied, herbivorous tortoises to highly aquatic, flat-bodied, carnivorous softshelled turtles. Most species used in laboratory research are
omnivorous and semi-aquatic. Crocodilians (alligators,
Harry W. Greene, Ph.D., is a curator of herpetology in the Museum of
Vertebrate Zoology and professor in the Department of Integrative Biology,
University of California, Berkeley.
182
caimans, crocodiles, and gavials) are semi-aquatic carnivores
and infrequently maintained in captivity outside of zoological parks. The 2 species of tuataras (Sphenodon) are confined to certain islands off the coast of New Zealand, very
rarely maintained in laboratory settings, and not dealt with
further here. The approximately 6,000 species of lizards,
amphisbaenians, and snakes are each others' closest relatives, collectively termed "squamates" or "squamate reptiles," and characterized as a group by the presence of 2
copulatory organs (called hemipenes) in males. Many species of lizards and snakes are widely used in research, resulting in thousands of publications annually. The best detailed
survey of reptile biology is still Bellairs (1969); for more
general but useful reviews, see Cogger and Zweifel (1992),
Pough and others (1989), and Zug (1993). The best entries
to the voluminous primary literature on reptiles are the annual volumes of Zoological Record. Recent edited volumes
by Murphy and others (1994) and Warwick and others (1995)
provide scholarly overviews of captive management and
welfare. Conant and Collins (1991) and Stebbins (1985)
provide concise introductions to the reptiles of the United
States.
With few exceptions (for example, some brooding females pythons), reptiles are ectothermic; this means that they
depend upon an external heat source to maintain body temperatures above ambient (note that some reptiles routinely
maintain fairly constant high temperatures for hours, such
that the term "cold-blooded" is inappropriate). Heating is
typically accomplished by basking, although some secretive
species heat themselves conductively under rocks and other
warm cover objects. Ectothermy and the generally low metabolic rates associated with that lifestyle have numerous important consequences for proper captive maintenance; for
example, a variable thermal environment is crucial for good
health, periods of torpor are acceptable, and frequent feeding
is not necessarily imperative. Most reptiles also rely substantially on chemosensory information in dealing with their
environments, meaning that anthropocentric perspectives
may be misleading in terms of proper care (Chiszar and others 1980; see Weldon and others 1994, for a review).
Reptiles vary in size from the 1 g adults of certain gecko
lizards (such as Sphaerodactylus) to several species of turtles,
crocodilians, lizards, and snakes that exceed 100 kg in mass.
Although all turtles, crocodilians, and tuataras lay eggs, several groups of lizards, amphisbaenians, and snakes have independently evolved viviparity; various forms of postnatal
parental care are exhibited by crocodilians and some
squamates. Natural lizard diets range from insects for most
small species to leaves for green iguanas (Iguana iguana)
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and mammals for some large monitors (Varanus). All snakes
are carnivores; some vipers consume individual prey items
in nature weighing up to 156% of their own weight.
SPECIES AVAILABILITY
General Comments
Reptiles often live many years in captivity, yet particular
species may be quite difficult to obtain without years of effort and once-in-a-lifetime opportunities. Consequently researchers conducting comparative studies often find it useful
to maintain individual reptiles for long periods during which
they are used for a variety of teaching and research purposes.
With the exception of the few species bred in captivity (such
as corn snakes [Elaphe guttata]) or readily available from
wild populations (such as green anoles [Anolis carolinensis]),
reptiles do not fit the widespread situation for mammals, in
which quantities are ordered for a specific short-term use,
sometimes on a moment's notice, and then discarded.
Commercial Vendors and Captive Breeding
Reptiles are available commercially from several national
and international firms, from thousands of pet stores in the
United States, and from countless individuals who collect or
breed them for commercial purposes. Many of these commercial outlets now advertise in national magazines (such as
The Vivarium) devoted to captive amphibians and reptiles,
recent issues of which can be obtained at most large metropolitan pet stores. The buyer must recognize that the legality
and professionalism of reptile vendors varies tremendously
and thus shop accordingly; patronizing firms that traffic in
illegal animals or that fail to maintain healthy stock encourages those unfortunate activities. Reputable zoological parks
can sometime provide surplus animals to other professional
organizations, although their charters often preclude subsequent invasive experiments with those individuals.
Field Collection
Most states and national governments regulate the taking of
live reptiles under certain conditions and issue permits for
such activities. Taking reptiles from the wild without applicable permits can lead to fines and even jail terms, and bringing illegally collected wildlife from other countries into the
United States is a federal crime subject to severe penalties.
The International Convention on Trade in Endangered Species (CITES) specifically applies to some reptiles (such as
gila monsters [Heloderma suspectum], boa constrictors [Boa
constrictor] and their relatives), such that additional permits
are required when obtaining these species in the wild and
transporting them across international boundaries. Levell
(1995) surveys regulations concerning collection and importation of reptiles.
Volume 37, Number 4
1995
Methods for finding and capturing amphibians and reptiles are essentially identical, and are well-covered in a recent
volume on research techniques for amphibians (Heyer and
others 1994). Common tactics include hand capture (sometimes assisted by a hand-held noose or net), pit-fall trapping,
and road driving. Two paramount issues are that collecting
should minimize habitat damage (for example, cover objects
should be returned to their exact resting places in order to
preserve the microhabitats under them) and that pit-falls, drift
fences, and other indirect methods must be designed and used
such that captured animals do not perish (for example, traps
should be shaded and checked frequently). Furthermore, wildcaught reptiles should normally not be released back into the
wild and should never be released in places where they were
not originally caught. In most states release is explicitly prohibited by law. Releasing animals after they have been captive
for substantial periods risks the introduction of potentially devastating parasites and diseases into wild populations; even if
healthy, most formerly captive animals probably would not
survive following release.
Shipping
The first requisite of proper shipping is a healthy animal.
Containers must be sturdy, provide sufficient ventilation, and
be thoroughly labeled with respect to contents and proper
handling; prominent notices to "keep from extreme heat and
cold" are especially important. Small harmless reptiles can
be sent by air mail, using the fastest means possible. Larger
animals and all snakes must be sent air freight, and venomous species require special packaging. Carriers should be
contacted in advance to learn applicable regulations and
schedules for shipping. Recipients should take pains to monitor a shipment's routing so that it can be retrieved promptly
and unpacked. Reptiles typically do not require feeding or
other temporary care during transport, although some species that desiccate easily will require special moist packing.
Food should be withheld for a period prior to shipping sufficient that digestion is complete before beginning the trip (for
example at least several days for most snakes, a day for most
lizards).
HUSBANDRY AND HOUSING
Caging
Caging should be adequately large, effectively cleanable,
and secure. Most lizards can jump (as can crocodilians!) and
virtually all reptiles (even turtles) can climb; snakes are veritable escape artists. Sizes and materials for enclosures will
vary depending on conditions for individuals species, with
due consideration to potential health hazards. For example,
many species will rub their noses raw against wire screen
enclosures, and some animals injure themselves while attempting to squeeze into cage crevices (such as where the
183
sides and top meet and where glass fits into metal frames on
aquaria).
Heating, Ventilation, Lighting, and Air
Conditioning
Many books on captive care, which include details of cage
design and other aspects of reptile maintenance, are now
readily available in large pet stores (Pough 1991; Mattison
1992; Murphy and others 1994; Warwick and others 1995).
Lizards often require some ultraviolet light, which must be
provided with special light fixtures (Townsend and Cole
1995). Reptiles vary so widely among species in their temperature and moisture requirements that they require individual planning in these regards. For example, southern alligator lizards (Elgaria multicarinata) prefer active
temperatures of approximately 22-24°C, whereas chuckwallas {Sauromalus obesus) and desert iguanas (Dipsosaurus
dorsalis) will not thrive unless they can heat up to 38^K)°C
for several hours daily. For most species proper long-term
maintenance requires some sort of thermal gradient, varying
both daily and within the cage. For example, cages can be
arranged on a shelf perpendicular to a timer-controlled heat
tape along the leading edge of the shelf. By maintaining
room temperature at the lowest desirable setting (equivalent
to nighttime cool values), reptiles can choose individually
preferred body temperatures during the day by simply moving to different parts of their cages. Extremely high temperatures are quickly fatal however, and a cool retreat must always be available.
Tolerance for desiccation and the use of free-standing
water vary tremendously among reptiles: sidewinder rattlesnakes (Crotalus cerastes) seemingly never drink, whereas
some tropical snakes will shrivel and die if left overnight in
an open container in an air conditioned lab. Water should be
provided in dishes or by misting the substrate as appropriate
for particular creatures (many reptiles will only drink by
lapping droplets, and some lizards will drown if provided
with water dishes [Schwenk and Greene 1987]). Water
sources and cage conditions must be manipulated to ensure
proper relative humidity; closed air systems can be especially desiccating and must be planned for accordingly.
Diet
Diets are widely variable among reptiles and often species
typical. Most turtles are omnivorous, although tortoises are
exclusively plant-eaters and softshells and some other aquatic
species are largely carnivorous. Crocodilians are all carnivorous, with the juveniles feeding on insects and small
vertebrates. Lizards eat insects, and a variety of sizes, shapes,
and nutritional attributes is often advisable. Amphisbaenians
typically feed on appropriately sized insects, although the
larger checkered amphisbaenian (Amphisbaena fuliginosa)
and yellow amphisbaenian (A. alba) will take small mice in
captivity. The vast majority of snakes regularly maintained
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in captivity do well on a diet of laboratory mice, and many
species that feed on frogs and lizards in the field can be
tricked into a regular diet of rodents. Guidebooks on the care
of particular species and original natural history literature
must be consulted for particular dietary requirements.
The use of mice as food for captive snakes raises several
issues. Most captive snakes readily take pre-killed rodents, a
procedure which some find ethically superior to feeding them
live prey and which also prevents mice from killing snakes if
the former are not eaten immediately (a definite risk). On the
other hand, teaching and research needs might dictate that
long-term captive snakes readily take and effectively dispatch live prey.
Sanitation
Drinking water for reptiles should be cleaned regularly and
be free of dangerous impurities. Cages should be cleaned
regularly, but not excessively, as at least lizards and snakes
probably use chemical cues as indicators of familiarity—too
frequent cleaning thus can be a source of stress (Chiszar and
others 1980). In some cases (such as green iguanas [Iguana
iguana]), juvenile herbivorous lizards even require ingestion
of adult feces to achieve appropriate gut floras (Troyer 1984).
A good general rule for effective captive sanitation is to
change substrates with sufficient frequency to prevent a
buildup of feces and to break down the cage for thorough
cleaning only as needed.
CAPTIVE BREEDING
Many species of turtles, crocodilians, and squamates are now
commonly bred in captivity. Captive breeding has the advantage of providing individuals of known history, typically
free of parasites and disease, and of reducing the demand for
collecting from wild populations. Effective captive breeding
depends on some knowledge of species-typical natural history, and usually involves manipulating temperature, humidity, and lighting conditions on a seasonal basis. Social situations must also be controlled; for example, some snakes
will not mate if they have been caged together for long periods, and conflict among males in the presence of a female
seems to be important in breeding various squamates. Captive breeding should be conducted only with a clear plan for
the offspring, as the latter must not be released into wild
populations. The popular books referred to earlier contain
the bulk of available literature on conditions for captive
breeding of reptiles.
SAFETY CONSIDERATIONS
Toxins and Other Weaponry
The vast majority of turtles and squamates are harmless to
humans. Claws and jaws of even moderate to large reptiles
ILAR Journal
can be injurious; an adult green iguana (Iguana iguana) and
even a small crocodilian or monitor can deliver an extremely
painful and scarring bite. Heavy gloves are appropriate for
handling these animals. Large constricting snakes (such as
pythons more than 2 m in total length) are potentially capable of killing an adult human by constriction in a matter of
a few minutes. At least 2 people should always be present
when large constrictors are managed.
Two species of venomous lizards—the gila monster
(Heloderma suspectum) and the beaded lizard (H. horridum)—
and perhaps 500 species of dangerously venomous snakes
(almost all of them in the Elapidae and Viperidae) are capable
of delivering potentially serious and even fatal bites. Many
states and some municipalities have regulations governing the
maintenance of venomous reptiles. Standard precautions include a posted snakebite protocol, information on the availability of appropriate antivenom, locks on all cages for venomous reptiles and heightened security for rooms containing
them, and restriction of access to trained personnel. Safe handling and well-being of the animals are ensured by never directly handling unanesthetized venomous snakes (see below).
Simple inspection not requiring anesthesia is facilitated by
coaxing a venomous snake part of the way into a plastic tube,
such that it can then be safely handled.
Zoonoses
Some turtles and lizards carry Salmonella (Grenard 1994).
Although the transfer of disease-producing organisms from
reptiles to humans is not regarded as likely, routine hygiene,
especially washing hands after handling the animals, is advisable.
syncratic color pattern markings (see Francini and others
1990, for an example with snakes in a lab colony).
ANESTHESIA, EUTHANASIA, AND
SURGERY
A number of injectable and gas anesthetics are applicable to
reptiles (see Pough 1991 for extensive references, and the
accompanying article by DeNardo, p 173 of this issue, for
general comments). The former have the advantage of simplicity, but often require long put-down and recovery times.
Halothane and other vapor anesthetics have the advantage of
rapid onset and recovery, and are widely used for both surgery and restraint of lizards and snakes (Reinert 1992). Although formerly widely used and perhaps viewed as especially practical, hypothermia is of questionable effectiveness
as an anesthetic for reptiles and not recommended (see article by Martin, p 186 of this issue for additional discussion
and references).
Cranial concussion and decapitation followed by double
pithing are acceptable methods for killing reptiles, but have
the disadvantages of being aesthetically unpleasant and
physically damaging to the specimen. Whenever appropriate drugs are available, reptiles can be humanely and effectively killed by an overdose of sodium pentobarbitol; the
drug can be administered to venomous snakes while they are
safely immobilized in a plastic tube (see above). Proper
training in all such procedures is imperative.
Standard surgical techniques are generally applicable for
reptiles, and reptiles generally withstand surgery without
complication. Because these animals are ectotherms and
healing processes are surely temperature dependent, provision of conditions for effective thermoregulation are crucial
for recovery.
IDENTIFICATION TECHNIQUES
Individual identification of captive reptiles ensures that each
animal is routinely monitored for health. In the case of wildcaught individuals, identification and accompanying collection data ensure their continued usefulness as museum specimens after death (Greene 1994). Cage cards provide an
expedient method when animals are housed individually, and
should be accompanied by the original collector's field tag in
the case of wild-caught individuals. Most marking methods
that apply to reptiles are surveyed in a recent manual on
amphibian research (Heyer and others 1994), with the proviso that toe-clipping appears to cause minimal discomfort
and is appropriate for small lizards. Unlike some amphibians, reptiles do not regenerate clipped toes. Turtles are
often marked by notching unique combinations in the marginal scutes of their shells, and snakes can be identified by
combinations of ventral scale clip scars. Microchip implants
("PIT" tags) have recently gained popularity for marking
small vertebrates, their applicability limited in some cases by
the small size of the animals and cost. An excellent and still
underused method for identifying individual reptiles is idioVolume 37, Number 4
1995
ANIMAL WELFARE REGULATIONS AND
POLICIES, BEHAVIORAL COMPLEXITY,
AND SUBTLE ETHICAL ISSUES
As "lower vertebrates," nonavian reptiles are exempt from
U.S. Department of Agriculture regulations. Nevertheless it
is widely recognized that humane considerations apply to
these animals, and published general guidelines are available
(Pough 1991). Recent studies expose a variety of complex,
often chemically mediated responses to conspecifics, surroundings, and so forth by captive and free-living reptiles.
For example, rattlesnakes exhibit a chemical sense of self
and possess an internal map of their surroundings, and a
captive turtle ceased destructive self-mutilation when provided with objects for manipulation (Chiszar and others
1993; Burghardt and Layne 1995; Warwick and others 1995).
Reptiles are widely and naively regarded as behaviorally
simple, and we probably routinely underestimate conditions
appropriate for their maintenance. It behooves us to take the
complexity of their lives in nature into account in designing
effective and humane conditions for their care in captivity.
185
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Acknowledgments
I appreciate critical comments on the manuscript by Kelly R.
Zamudio.
Evaluation of Hypothermia for Anesthesia in Reptiles
and Amphibians
Brent J. Martin
INTRODUCTION
When reviewing research proposals involving ectothermic
animals, members of institutional animal care and use committees (IACUCs) are frequently required to evaluate husbandry methods and research techniques that are not well
known to them. Gathering additional information on these
techniques is often unrewarding due to the paucity of published accounts and the tremendous diversity among ectotherms.
One such topic of concern is the use of hypothermia for
Brent J. Martin, D.V.M., is the Director, Department of Animal Resources,
Vivarium, University of California, Santa Barbara, California.
186
anesthesia. This anesthetic method has been used for over a
century (Blair 1971) and is still often proposed by investigators who use amphibians and reptiles. IACUC members
frequently express discomfort with the adequacy of this
method; they may be unfamiliar with and lack specific
knowledge about hypothermia and may suspect that it is insufficient to render an animal insensible to painful procedures such as surgery. Investigators may base their arguments for its use on past successful experiences where the
hypothermic animal failed to respond to any stimuli. Investigators may also have experienced better survival rates with
hypothermia than with traditional anesthetics. The scientific
literature is replete with references to hypothermia used for
anesthesia, and there are some concerns that anesthetics can
adversely affect an experiment (Smith and others 1991).
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