Glass frogs are frogs of the amphibian family Centrolenidae (order Anura). Although the general background coloration of most glass frogs is primarily lime green, the abdominal skin of some members of this family is transparent and translucent
The internal viscera, including the heart, liver, and gastrointestinal tract, are visible through the skin, hence the common name crystal frog. However, their transparency is compromised once on land. They are considered translucent rather than truly transparent. Glass frogs are arboreal, meaning they live primarily in trees and only come out for the mating season.
Characteristics of Glass Frogs
Glass frogs are usually small, ranging from 3 to 7.5 cm in length. They are green on most of their body, except for the skin on the undersurface of the body and legs, which is transparent or translucent.
Glass frogs are similar in appearance to some green frogs of the genus Eleutherodactylus and some tree frogs of the family Hylidae. However, Hylidae tree frogs have eyes that face sideways, while those of glass frogs face forward
Some species of green treefrogs (especially juveniles), such as Hyloscirtus palmeri and Hypsiboas pellucens, have the transparent abdominal skin typical of glass frogs, but also have calcars on the heels, a character that is not present in any species of the Centrolenidae.
Two members of the glass frog family Centrolenidae (Centrolenella fleischmanni, C. prosoblepon) and the hylid subfamily Phyllomedusinae (Agalychnis moreletii, Pachymedusa dacnicolor) reflect near-infrared light (700 to 900 nanometers) when examined by infrared color photography
Infrared reflectance may confer an adaptive advantage to these tree frogs in both thermoregulation and cryptic infrared coloration.
The evolutionary advantage of a partially clear skin, but with an opaque dorsum, was a mystery, as it did not appear to be effective as camouflage. It was found that the frog’s body color changed little in the face of darker or lighter foliage, but the legs were more translucent and consequently changed in brightness.
When resting with translucent legs surrounding the body, the frog’s edge appears smoother, with less of a brightness gradient from leaf to legs and from legs to body, making the outline less noticeable
Experiments with computer-generated images and gelatin models of opaque and translucent frogs found that translucent frogs were less visible and were attacked by birds much less often.
Habitat and behavior
The Centrolenidae are a diverse family, distributed from southern Mexico to Panama, and across the Andes from Venezuela and Tobago Island to Bolivia, with some species in the Amazon and Orinoco river basins, the Guiana Shield region , southeastern Brazil and northern Argentina.
Glass frogs are primarily arboreal. They live along rivers and streams during the breeding season, and are particularly diverse in the montane cloud forests of Central and South America, although some species are also found in the rainforest and semi-deciduous forests of the Amazon and Chocó.
Hyalinobatrachium valerioi glass frogs are carnivorous, their diet includes mainly small insects such as crickets, moths, flies, spiders and other smaller frogs.
Eggs are usually deposited on the leaves of trees or bushes overhanging running water in mountain streams, creeks and small rivers. One species lays its eggs on rocks near waterfalls
The method of laying eggs on the leaf varies by species. Males usually call from leaves near their clutches.
These eggs are less vulnerable to predators than those laid in water, but are affected by the parasitic worms of some fly species
In many species, female glass frogs hatch their eggs during the night when they are fertilized, which improves egg survival, while in about one-third of the species, male glass frogs remain on guard for much longer periods. Once hatched, the tadpoles fall into the waters below. The tadpoles are elongated, with powerful tails and low fins, suitable for fast water. Outside the breeding season, some species live in the canopy.
