Silverstone's Poison Frog, Rana Venenosa
© 2007 Dr. Peter Janzen (1 of 5)
Description:Male adults are large and have a maximum snout-vent length of 38.3 mm. Females are typically slightly larger than males with a maximum snout-vent length of 42.8 mm. The head is generally as wide as the body and is characterized with a sloping and rounded snout. Teeth are present on the maxillary arch. Adult males possess a shallow subgular sac and have well-developed vocal slits in the mouth. The tympanum is concealed post-dorsally. The skin of the lower body and hind limbs is coarsely granular, gradually smoothing out in the skin of the head, forelimbs and ventral surfaces. The fingers are appressed and have a relative length of 3>4≥1≥2, each terminating in small expanded discs. Hands and feet lack webbing (Myers and Daly 1979).
Coloration:Adults have an orange or red head and body and may have heavy black spotting or marbling. Hind limbs are all or partly black, and may have a concealed calf spot. The undersides of the head and body of A. silverstonei are variably pigmented, ranging from black to uniformly pale orange. Palms and the undersides of the fingers also vary from gray to bright orange (Myers and Daly 1979).
Tadpole Morphology: Tadpoles are grayish or blackish-brown, with a few smatterings of darker spotting. The beak of the tadpole is keratinized, but does not appear of considerable size. The mouth has delicately toothed edges, and the lower beak has a broad V-shape. They have a single row of pointed papillae. As they age, late tadpoles acquire dull yellow pigmentation on their forelimbs, snout, and upper eyelids. The dark brown of the larvae darkens to black as they become froglets and the yellow changes to light orange, and sometimes into red thereafter. The orange area expands over the head and torso. This pattern is developed within a month or so, and expansion of the orange-reddish areas occurs after twelve months (Myers and Daly 1979).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
To defend against predators, skin secretions contain small amounts of pumiliotoxin-A alkaloids, a toxin found in the skin of poison frogs. However, the secretions lack the more potent batrachotoxin alkaloids. Despite lacking great potency, A. silverstonei has bright coloration which deters predators. In one observation, a frog-eating snake (Chironius sp.) of the Cordillera Azul area, seized and then immediately released a member of the species. Afterwards, the snake seemed disoriented and tried to rub out its mouth with branches, indicative of the toxic deterrent in the frog’s skin. However, the poison was not fatal and the snake seemed to recover fully. Not much more is known of the predators of A. silverstonei (Myers and Daly 1979).
Trends and Threats
Although there is not enough data to determine population size and whether or not it is declining, it has been observed that these frogs have a preference for living in undisturbed forests (Myer and Daly 1979). This makes them vulnerable to agriculture, logging operations, and road constructions that border their habitat.
Relation to Humans
Possible reasons for amphibian decline
General habitat alteration and loss
Synonymy/Taxonomy:Ameerega silverstonei was originally classified as the genus Phyllobates and species bicolor. In 1976, Philip A. Silverstone observed that P. bicolor was restricted to the northern Andes of Colombia and it was therefore highly unlikely that the Peruvian frog was related to the Colombian P. bicolor. In 1979, Charles Myers and John Daly proposed that the frog be named after Silverstone for making this distinction. The frog was first put in the genus Epipedobates and was known for some time as E. silverstonei. Presently, it is recognized as a member of the genus Ameerega and is now known as Ameerega silverstonei (Myers and Daly 1979).
Myers, C. W. and Daly, J. W. (1979). ''A name for the poison frog of Cordillera Azul, eastern Peru, with notes on its biology and skin toxins (Dendrobatidae).'' American Museum Novitates, 2674, 1-24.
Stuart, S., Hoffmann, M., Chanson, J., Cox, N., Berridge, R., Ramani, P., and Young, B. (eds) (2008). Threatened Amphibians of the World. Lynx Edicions, IUCN, and Conservation International, Barcelona, Spain; Gland, Switzerland; and Arlington, Virginia, USA.
Written by Diana Lakeland, Fabiola Galvan Torres, Tracy Rosenthal (dslakeland AT ucdavis.edu, ftgalvan AT ucdavis.edu, trosenthal AT ucdavis.edu), UC Davis
First submitted 2010-10-14
Edited by Kandys Kim (2012-02-14)
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