Conservation Spotlight

Tomato Frogs

By: A. Wisnieski, V. Poole, and E. Anderson

The Madagascar Tomato Frog (Dyscophus antongilli) is a rather large terrestrial microhylid that ranges along the northeastern coast of Madagascar from Antongil Bay south to Andevoranto. They occur at elevations from sea level to 200 meters and breed in shallow pools, swamps, drainage ditches, and slow moving bodies of water.

A sexually dimorphic species, female tomato frogs range in size from 8.5 to 10.5 cm and are solid bright red or orange dorsally, which shades into a white ventral surface. Males are not as large (6 to 6.5 cm) or as brilliantly colored, being a duller yellow-orange. A toxic, whitish skin secretion is used as a defense against predators, and can occasionally produce allergic reactions in humans.

Dyscophus antongilli is endangered in its native country as a result of deforestation and over-collecting for the pet trade, and is now listed on Appendix I of the Convention on International Trade in Endangered Species (CITES). There are two other species of tomato frogs in Madagascar, D. guineti and D. insularis, neither of which are presently endangered.

Because of their endangered status and appeal, this species has been designated as high priority by the AZA Amphibian Taxon Advisory Group (TAG) and is a flagship species for the Madagascar Fauna Group, a consortium of U.S. zoos, including The Baltimore Zoo, dedicated to the preservation of threatened fauna and natural habitats of this unique island country. The captive population in U.S. zoos, currently 101 adult specimens in 21 institutions, is jeopardized by a lack of genetic diversity, unknown pedigrees, and until recently, a shortage of animals.

In an effort to preserve the species in captivity, The Baltimore Zoo spearheaded a collaborative effort in 1994 by arranging for shipment of tomato frogs to the University of California at Berkeley from the Chaffee Zoological Gardens of Fresno, Ft. Worth Zoological Park, Sedgwick County Zoo, Woodland Park Zoological Gardens, and two private collections. There, under the direction of Dr. Dale Denardo, researchers successfully induced reproduction utilizing hormones, producing 255 froglets from two spawnings.

The Baltimore Zoo received 14 of these offspring in December of 1994 with the goal of reproducing tomato frogs naturally, through environmental manipulation, as the use of hormones can sometimes produce adverse side effects. The frogs were reared in terraria (61 cm x 30.5 cm x 45 cm) equipped with drains, using a sheet moss substrate over a pea gravel bed that was sloped at one end to create a shallow pool and supported by a filter plate to facilitate cleaning and drainage. Plants, plastic huts, and cork bark were used to provide hiding spots. The frogs were fed crickets twice a day, which had been gut loaded with Zeigler Cricket Diet and dusted with a vitamin/mineral powder consisting of NektonR Rep, NektonR MSA, and RepcalR D in equal proportions. They were also misted twice daily with dechlorinated tap water and full spectrum florescent lighting was provided.

By 1995, the frogs were large enough to be sexed based on size and coloration differences, and potential breeding groups of four males and two females were established in two 122 cm x 61 cm x 61 cm terraria. Enclosure temperatures and photoperiod ranged seasonally from 21 to 26 C and 9.5 to 16 hours of daylight, respectively. Enclosures were also misted to maintain a relative humidity of 70 to 90%.

Six months prior to planned breeding attempts, staff attempted to stimulate reproduction by maintaining the frogs at a drier relative humidity (55 to 65% average). This was accomplished by decreasing the pool depth and mistings, and increasing cage ventilation. On May 23, 1997, the pool depth was increased to 8 cm, the lights were dimmed, and a misting system and humidifier were added to simulate rain storms that are the catalyst for natural tomato frog reproduction. By the next morning, the males had begun calling and amplexing the females.

On May 28, approximately 4700 eggs were found in one of the enclosures. To prevent the still calling and amplexing adults from destroying the egg mass, the adults were removed to another terrarium. The eggs began hatching within two days, and in order to minimize crowding, the majority of the 1 cm long tadpoles were separated into large RubbermaidR tubs with sponge filters for rearing. Spirulina flakes, AquarianR Tropical flakes, and TetraR basic staple flakes were offered twice daily. Water chemistry was monitored daily and water changes were performed as needed.

The first froglets began to metamorphose on July 1, and averaged 15.22 cm in snout-vent length and 0.49 g in weight. They were primarily black in color with a tan dorsal streak. It typically takes several months for them to acquire their distinctive orange-red coloration. The froglets were fed pinhead crickets and fruit flies dusted with our vitamin/mineral mixture and misted daily. By two months of age, most of the froglets had already begun to eat two-week-old crickets. The frogs produced from this spawning have been placed in the collections of other U.S. zoological institutions with the intention of pairing them with frogs from different bloodlines when they become available.

In addition to captive reproduction efforts, The Baltimore Zoo is actively involved in several other tomato frog conservation projects. For example, to educate the Malagasy people on the plight of this endangered species and to combat the challenges of insufficient genetic diversity in the captive U.S. zoo population, The Baltimore Zoo has funded the construction of a tomato frog exhibit in Parc Zoologique Ivoloina, a zoo in Madagascar. This was accomplished by working through the Madagascar Fauna Group. Significantly, this is the first and only exhibit for an amphibian species in the entire country. It features eight wild-caught tomato frogs that zookeepers there will attempt to breed so offspring may be available to zoos abroad. Photographs of The Baltimore Zoo's tomato frogs have been provided for the educational graphics at the New Parc Ivoloina exhibit. The graphics will help to educate their visitors about the preservation of this endangered species and its habitat, as very few people in Madagascar are aware of the threats to its survival.

The Baltimore Zoo has also provided funding for Dr. Edward Louis of Omaha's Henry Doorly Zoo to perform DNA testing on blood samples taken from tomato frogs in U.S. zoos with unknown pedigrees. This will enable zoos to determine exact lineages for all captive tomato frogs, so they can breed pairs that provide maximum genetic diversity in the captive population. Additionally, The Baltimore Zoo is also working towards exchanging tomato frogs with the Copenhagen Zoo so that European and U.S. institutions can benefit from shared bloodlines.

For additional information on Tomato Frogs or any of the projects mentioned, contact Anthony Wisnieski, Curator of Reptiles and Amphibians, or Vicky Poole, Assistant Curator, The Baltimore Zoo, Druid Hill Park, Baltimore, MD 21217. Telephone (410) 396-0441 or FAX (410) 545-7397.

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