ILAR Journal Online, Volume 37(4) 1995: Fish, Amphibians and Reptiles

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ILAR Journal V37(4) 1995
Fish, Amphibians and Reptiles

Nonavian Reptiles as Laboratory Animals
Harry W. Greene

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.

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--in-deed 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 chelo-nians) range from strictly terrestrial, dome-bodied, herbivorous tortoises to highly aquatic, flat-bodied, carnivorous soft-shelled turtles. Most species used in laboratory research are omnivorous and semi-aquatic. Crocodilians (alligators, 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) 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 gutrata]) 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.

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, wild-caught 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 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 chuckwal-las (Sauromalus obesus) and desert iguanas (Dipsosaurus dorsalis) will not thrive unless they can heat up to 38-40°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 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 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. horridurn)-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.

IDENTIFICATION TECHNIQUES

Individual identification of captive reptiles ensures that each animal is routinely monitored for health. In the case of wild-caught 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 idiosyncratic 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.

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.

ACKNOWLEDGMENTS

I appreciate critical comments on the manuscript by Kelly R. Zamudio.

REFERENCES

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