Introduction

Small, brightly-colored frogs of the Family Dendrobatidae are found in tropical central and South America (Silverstone, 1975). Among the remarkable qualities of some of the adult frogs is their production of defensive secretions of toxic or noxious alkaloids from cutaneous glands. These unique alkaloids are used by Amerindian hunters as poison for their blowgun darts, hence the common name for the entire family of frogs poison dart frogs, poison arrow frogs, or simply poison frogs. In addition to their use by hunters, the alkaloids are also the subject of toxicological and pharmacological study. For some species of poison-arrow frog, such as Phyllobates terribilis, production of toxic alkaloids is high in wild caught animals, reduced during maintenance in captivity, and absent in captive bred animals (Daly et al., 1980; 1987). The latter phenomenon may limit the scope of pharmacological investigations. Daly et al. (1987) have suggested that symbiotic microorganisms or other environmental factors may play a necessary role in the initiation of alkaloid biosynthesis during ontogeny.

Two of the five genera of poison arrow frogs, Dendrobates and Phyllobates, are threatened with extinction. This danger, plus the desire to have access to dendrobatids for scientific study, has prompted the maintenance and captive breeding of these frogs. Within the United States, the most successful breeding program is at the National Aquarium in Baltimore.

It is known that frogs and toads are hosts to many different protozoans, especially flagellates, opalinids, and ciliates; some protozoana may be pathogenic. However, little is known of the fauna of dendrobatids, either in the wild or in captivity. Our recent literature search has uncovered only two publications dealing with the protozoan fauna of dendrobatid frogs (Guerro & Ayala, 1977; Metcalf, 1923). In view of the threat to the survival of the frogs, and the paucity of information on their protozoan fauna, we are surveying the protozoa infecting two species of Dendrobates occurring in the rain forests of Costa Rica, and also maintained at the National Aquarium in Baltimore.

Materials and Methods

The two species of Dendrobates we are studying are Dendrobates auratus, the black and green poison arrow frog, and Dendrobates pumilio, the strawberry poison arrow frog. The former species, upon which most of our attention is focused, has been selected because it is one of the largest dendrobatids, is locally abundant in regions of Costa Rica, and is easy to breed in captivity. The latter species has been selected because it is also locally abundant in the same regions of Costa Rica as Dauratus.

Our aim is to identify the symbiotic protozoa infecting the frogs, and compare the fauna of wild caught and captive bred frogs. We will focus particularly on the protozoa inhabiting the blood and digestive tract, and we are preserving samples of metazoa and of other tissues for study by other investigators. The length weight and sex of the frog noted, so that we may determine any relationships between infection and condition of the host.

Blood smears are examined both fresh and after staining with Giemsa. The intestine is examined in a number of ways: fresh smears, Protargol (silver-protein) stained preparations, scanning electron microscopy, transmission electron microscopy, and histological sections. Semi-quantitative estimates of protozoa densities will be made and the species mix in the intestine recorded.

Our initial studies have been of D. auratus and D. pumilio wild caught from Costa Rica, and subsequently maintained at the National Aquarium in Baltimore. In the next year we will focus on comparison of the wild caught and captive bred D. auratus.

Results

Dendrobates auratus is host to the hemoflagellate Trypanosoma sp. The Intestinal. fauna is very diverse, and includes several kinds of flagellates including a euglenoid and two trichomonads, an opalinid belonging to the genus Zelleriella and a large ciliate tentatively identified as Nyctotheroides. The intestinal protozoa have been examined by Protargol, and scanning and transmission electron microscopy. In D. pumilio, hernoflagellates have not been seen, and the intestinal fauna is less diverse than that in D. auratus, being almost exclusively flagellates. Protargol and ultrastructure studies are in progress.

Discussion

We believe that the protozoa encountered thus far are harmless commensals rather than pathogenic parasites. The fauna was similar in frogs in good condition and ill those that were emaciated. Nonetheless, we believe that more comprehensive knowledge of the fauna will help us understand which symbionts may be helpful to the frogs, and which may be harmful. This knowledge will provide the basis for the most appropriate care and veterinary treatments for the frogs maintained in captivity.

Acknowledgements

The financial support of the National Science Foundation and the National Aquarium in Baltimore is gratefully acknowledged. We would also like to thank Mr. Jack Cover, Curator of Rain Forest Exhibits at the National Aquarium, for his interest in the project, and maintenance of the frogs. Ms. Karen Walker, and members of the Protozoology laboratory at the University of Maryland at College Park, have assisted with preparation of the Protargol stains.

References

1.  Daly, J.W., Myers, C.W., Warnick, J.E., & Albuquerque, EX 1980. Levels of batrachotoxin and lack of sensitivity to its action in poison-dart frogs (Phyllobates). Science 208: 1383 - 1385.

2.  Daly, J.W., Myers, C.W., & Whitaker, N. 1987. Further classification of skin alkaloids from neotropical frogs (Dendrobatidae), with a general survey of toxic / noxoius substances in the amphibia. Toxicon, 25, 1023 - 1095.

3.  Guerro, S. & Ayala, S.C. 1977. Hemoparasites de algunos reptiles y antifios de le selva amazonica de Peru. Revista do Instituti de Medicine Tropical de Sao Paulo 19, (5) 283 288.

4.  Metcalf, M.M. 1923. The opalinid ciliate infusorians. Bulletin of the United States National Museum 120: 1 - 471.

5.  Silverstone, P.A. 1975. A revision of the poison-arrow frogs of the genus Dendrobates Wagler. Natural History Museum of Los Angeles County, Science Bulletin 21 (June 30), 1-55.