Australian frogs become "moisture farmers" to stay alive in droughts

Frogs in northern Australia have to find a way to survive months of cold, dry climate. Their solution? Hang around outside just long enough to trap condensation, which they use to hydrate themselves. By any standard, this is pretty ingenious.

Green tree frogs live in the tropical savannas of northern Australia. For much of the year, the living is pretty easy, but things get tricky in the dry season, when temperatures drop and there's little water to be found. As is typical for amphibians, these frogs drink using their entire bodies, and that puts them in a tricky situation. Their porous skin needs to be surrounded by water for the frogs to hydrate properly, and they risk dying of dehydration if they remain exposed to dry conditions for too long.

That's why it's so strange that the frogs actually venture outside their warm, humid dens in the middle of night to brave the dry, frigid exterior. At first blush, it's the sort of behavior that seems downright suicidal, but there's a rather brilliant method to this apparent madness. By stepping outside, the frogs can coat themselves in a thin layer of frost. When they venture back inside their dens - which are about 20 degrees Fahrenheit warmer and reach 90 to 100% humidity - the frost condenses into water, just like morning dew.

It's a cool theory, and now researchers at the University of Melbourne have found evidence to support it. To replicate these conditions, they placed frogs in the cool night air or in ice baths. Once the frogs were suitable chilled, they were then put inside dens, and they became coated in condensation. More importantly, the frogs were indeed drinking in the water, gaining an additional 1% of body mass after just 15 minutes in the tree.

According to the researchers' calculations, this dew harvesting isn't a terribly efficient process, and that the water gained back by collecting condensation is only just enough to offset all they lose from evaporation while hanging around outside. It also appears that the frogs need to have a very fine-grained sense of just when to use the condensation trick - if the den isn't warm enough or if the night is too cold, they could end up losing more than they gain, and that could soon be fatal. Basically, you should never underestimate a thirsty green tree frog.

Via ScienceNOW. Image via.