Amphibian Biology and Husbandry
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Amphibian Biology and Husbandry F. Harvey Pough Abstract Introduction Extant amphibians comprise three lineages—salamanders mphibians have a long history of service as research (Urodela or Caudata), frogs and toads (Anura), and caecil- animals, especially as models for studies of embry- ians (Gymnophiona, Apoda, or Caecilia)—which contain Aonic development, regeneration, and physiological more than 6000 species. Fewer than a dozen species of function. Salamanders (especially ambystomatids and sala- amphibians are commonly maintained in laboratory colo- mandrids) and frogs (notably ranids and Xenopus) have con- nies, and the husbandry requirements for the vast majority tributed much to these studies, and methods for maintaining of amphibians are poorly known. For these species, a review them in the laboratory are well established (Nace et al. of basic characteristics of amphibian biology supplemented 1974, O’Rourke 2002). Reviews of techniques for maintain- by inferences drawn from the morphological and physi- ing, breeding, and rearing these species of amphibians in ological characteristics of the species in question provides a captivity appear elsewhere in this ILAR Journal issue basis for decisions about housing and feeding. Amphibians (Browne and Zippel 2007; Browne et al. 2007; O’Rourke are ectotherms, and their skin is permeable to water, ions, 2007). Discussions of the requirements of some amphibians and respiratory gases. Most species are secretive and, in that are less commonly kept in captivity include the follow- many cases, nocturnal. The essential characteristics of their ing: Buchanan and Jaeger (1995), Cover et al. (1994), de environment include appropriate levels of humidity, tem- Vosjoli (1999), Johnson (1994), Maruska (1994), Pough perature, and lighting as well as retreat sites. Terrestrial and (1991), Wake (1994), Zimmermann (1986), and Zimmer- arboreal species require moist substrates, water dishes, and mann and Zimmermann (1994). high relative humidity. Because temperature requirements Increased interest in organismal biology and in environ- for most species are poorly known, it is advisable to use a mental and evolutionary physiology has brought novel spe- temperature mosaic that will allow an animal to find an cies into the laboratory. These species often are selected for appropriate temperature within its cage. Photoperiod may study because they have particular ecological, environmen- affect physiology and behavior (especially reproduction and tal, or phylogenetic characteristics. Because investigators hibernation), and although the importance of ultraviolet and others have usually collected the animals from the wild, light for calcium metabolism by amphibians is not yet the individual animals have no history of exposure to cap- known, ecological observations suggest that it might be im- tivity, and as species, they have not experienced selection portant for some species of frogs. Some amphibians are for tolerance of captivity. territorial, and some use olfactory cues to mark their terri- Currently there are no established husbandry methods tory and to recognize other individuals of their species. All for most species of amphibians, and only scanty information amphibians are carnivorous as adults, and the feeding re- is available about ecology and behavior for many of them. sponse of many species is elicited by the movement of prey. Meeting the basic physical needs of a species—terrestrial or Diets should include a mixture of prey species, and it may aquatic conditions, and the appropriate temperature and hu- be advisable to load prey with vitamins and minerals. midity—is obviously important, but other issues may be equally significant. Stimuli that elicit behavioral responses, Key Words: amphibian; caecilian; care; frog; herpetocul- for example, may inadvertently increase stress. The social ture; husbandry; salamander; toad behavior of amphibians is substantially more complex and subtle than one would guess from observations of laboratory colonies of Xenopus and axolotls (Ambystoma mexicanum and Ambystoma tigrinum). Social behaviors such as territo- riality and dominance hierarchies may influence feeding and reproduction (e.g., Gabor and Jaeger 1995, Jaeger and Schwarz 1991, Jaeger et al. 1995, Murray and Jenkins 1999, F. Harvey Pough, Ph.D., is Professor of Organismal Biology, Department Simons et al. 1997). Olfactory stimuli deposited on the sub- of Biological Sciences, Rochester Institute of Technology, Rochester, NY. Address correspondence and reprint requests to Dr. F. Harvey Pough, strate or carried through the air are elements of the behav- Department of Biological Sciences, Rochester Institute of Technology, 85 ioral ecology of some species of salamanders (Jaeger 1986). Lomb Memorial Drive, Rochester, NY 14623, or email [email protected]. Lighting conditions may also be more important than we Volume 48, Number 3 2007 203 realize—photoperiod as well as the intensity and spectral Phylogenetic and Ecological Diversity quality of light are probably important stimuli for some amphibians. A recent revision of the extant amphibians (Frost 2006) has Caring for exotic species of amphibians has much in resulted in a change of the generic names of many species. common with herpetoculture, and herpetocultural resources The literature of amphibian biology uses the old names, and can be useful sources of information and advice. Recom- literature searches require these names. To minimize con- mended resources include the Herpetocultural Library (de fusion, I have used the familiar names with the new names Vosjoli 2004, 2006; de Vosjoli et al. 2005); web sites (e.g., in parentheses. www.pumilio.com); and chat groups (e.g., www.groups The extant amphibians illustrate an approach to terres- .msn.com/HerpetocultureChatGroup/amphibians.msnw). In trial vertebrate life that combines ectothermy and a low addition, information about the ecology, geographic ranges, metabolic rate with highly efficient secondary production and conservation status of amphibians is available from (Pough 1983). A low metabolic rate reduces the mass- Amphibiaweb (www.amphibiaweb.org) and Global Am- specific metabolic rate with the result that small body size is phibian Assessment (www.globalamphibians.org). energetically feasible. Most amphibians are small. Twenty Herpetological Review, which the Society for the Study percent of the species of salamanders and 17% of frog spe- of Amphibians and Reptiles publishes, includes a section on cies have adult body masses of1gorless, and 65% of Herpetological Husbandry; and the International Zoo Year- salamanders and 50% of anurans are smaller than5gas book includes information about the care of amphibians. adults. Because they are ectotherms, amphibians do not use Professional staff members at zoos and aquaria may be able ingested energy to control their body temperature. As a to provide suggestions about the husbandry of particular result, their net secondary production efficiency is high— species. amphibians convert half or more of the energy they ingest When species-specific information about the behavioral, into their own body mass compared with less than 1% for ecological, and physiological characteristics of a species of birds and mammals. The combination of small body size amphibian is not available, inferences based on elements of and efficient biomass production allows amphibians to play the basic biology of amphibians may provide the only a unique role in ecosystems by consuming prey items that guidelines. Two characteristics of amphibians—ectothermal are too small for other vertebrates to eat and by repackaging regulation of body temperature and permeable skin—play most of that energy into salamander and frog-size packages central roles in their biology and provide starting points for (Pough 1980). inferences about their requirements in captivity. It is pos- The skin of amphibians lacks scales, is plentifully sup- sible to amplify these general characteristics with informa- plied with mucus and poison glands, and is a site of oxygen tion about the phylogenetic relationships and by and carbon dioxide exchange for adults as well as for larvae. observations of the morphological characteristics of the spe- Small body size and glandular skin profoundly influence the cies in question. ecology, physiology, and behavior of amphibians. Cutane- ous respiration accounts for a significant proportion of re- Biological Characteristics and Life Style spiratory gas exchange, water evaporates from the skin of of Amphibians some amphibians as rapidly as from a free-water surface, and amphibians are sensitive to toxins in the environment The extant amphibians (Amphibia [Frost 2006] or Lissam- (Alford and Richards 1999; Boutilier et al. 1992; Maerz et phibia [Tree of Life Web Project 1995]) appear in the fossil al. 2005; Shoemaker et al. 1992). record during the Mesozoic. A large number of derived The discussion that follows emphasizes features that are characters (initially identified by Parsons and Williams helpful starting points for inferences about the habits, habi- [1963] and subsequently restated and modified [Duellman tats, and husbandry of unfamiliar species of amphibians. and Trueb 1985, Frost 2006]) support the monophyly of the group. The lower Triassic form Triadobatrachus forms a Frogs and Toads monophyletic group with frogs and toads (Rage and Rocˆek 1989). The earliest salamander fossils are from Middle Ju- Anurans are the largest group of amphibians. Approxi- rassic sites in England and