13 April 2006

Paper read today: frogs wrapped in cocoons

"We use only the finest baby frogs, dew-picked and flown from Iraq, cleansed in the finest quality spring water, lightly killed, and then sealed in a succulent Swiss quintuple smooth treble cream milk chocolate envelope, and lovingly frosted with glucose."
Monty Python's Flying Circus Crunchy Frog

The physiological and morphological adaptations invertebrates and smaller vertebrates have evolved to survive the harsh physical conditions of terrestrial life have always fascinated me. Today’s paper review is along those lines and is about how certain Australian frogs survive dry conditions.

PC Withers & GG Thompson. Cocoon formation and metabolic depression by the aestivating hylid frogs Cyclorana australis and Cyclorana cultripes (Amphibia: Hylidae). Journal of the Royal Society of Western Australia, 83:39-40, 2000. (pdf)

Several species of Australian burrowing frogs ( Cyclorana spp.) cover their bodies with a cocoon when aestivating during dry periods. The multi-layered cocoons form from outer epidermal cells that the frogs seem to shed in layers; the longer they aestivate, the more layers they add. The cocoons made by the 2 species of frogs that were the subjects of this study, Cyclorana australis and Cyclorana cultripes, during 46 and 51 days of aestivation in the laboratory, had 34 and 32-33 layers (erroneously given as 51 in the abstract, see Table 1), respectively. The cocoons cover their entire bodies, including the eyes, mouth and cloaca, except for the openings of their noses.

During aestivation in the lab, the oxygen consumption rate of Cyclorana cultripes fell significantly by 70%. In both species, evaporative water loss decreased from about 15 to about 1.1 mg/g x hour. My only criticism of the paper is that the aestivation conditions in the lab were not clearly described, especially the ambient humidity was not reported.

According to the paper, some species of these frogs may aestivate in the wild for more than a year waiting for the rains. Do they keep adding layers to their cocoons during the entire aestivation period? The shedding of so much skin must be costly. I wonder if they eat their cocoons after they revive.

1 comment:

pascal said...

If we took the bones out it wouldn't be crunchy, would it.