This summer, while in Costa Rica, Steinhart aquarium biologists were privileged to encounter a variety of glass frogs, Family Centrolinidae. These frogs are appropriately called glass frogs because of the see-through nature of their skin. Although glass frogs have some pigment in their skin, mostly green, it is possible to see through their bellies and observe their organs.
Above: Hyalinobatrachium colymbiphyllum
Glass frogs breed and lay their eggs on leaves overhanging water, usually streams. Eggs may be predated on by insects and so the male sticks around to protect the eggs.
Above: Cochranella granulosa eggs develop on a leaf over a stream at the Costa Rica Amphibian Research Center, located on Costa Rica’s Carribean slope.
Above: Hyalinobatrachium valerioi male gaurds eggs on a leaf above a stream on Costa Rica’s Pacific slope.
Snakes also may eat the eggs. We observed this snake, Dipsas longiferis eating the eggs of a granular glass frog, Cochranella granulosa. It is unlikely that the attending male could do anything to protect his eggs in this case. We did not observe him nearby.
Above: Dipsas longiferis was seen eating a glass frog egg mass above a rainforest stream.
When the eggs hatch they fall into the stream below. The tadpoles lack pigment and as a result are red in coloration. While many tadpoles are dark in color and active in the water column or on the bottom of ponds or streams, glass frog tadpoles seem to be adapted well to life under rocks and other cover in streams.
Above: Cochranella granulosa tadpole. Note the reduced eyes, long , strong swimming tail and lack of pigment.
Just before the tadpoles metamorphose into tiny little frogs their eyes begin to enlarge, their hind legs grow in and their digestive tracks change from one well suited to eating vegetation to one that will exclusively feed on animal prey.
Above: Cochranella granulosa tadpole has developed legs, large eyes and the vertebrae are much thicker than those of earlier stage tadpole.
Above: Cochranella granulosa tadpoles at different stages of development. Note the one on the left has started to develop the typical characters of a frog, though the mouthparts are still distinctly tadpole. The one on the right is much less developed with its spiral shaped gut being its most obvious characteristic.
Above: This Cochranella granulosa has its front legs and is now a terrestrial animal, despite having not yet absorbed its strong swimming tail.
Above: This Cochranella granulosa has nearly absorbed all of its tail. Within the next several days it will start feeding on bugs—an entirely different diet than it has ever had before.
During our trip we saw several species of glass frog. We were fortunate to bring back two species for exhibit. Currently, we are growing out tadpoles which will be the founders of a captive population that will supply our exhibits in the years to come.
Above: Teratohyla spinosa on the Carribean slope of Costa Rica.