Outwardly, the tiny wood frog, Rana sylvatica, does not look like your regular arctic inhabitant. Yet despite their tiny stature, these little frogs are actually quite hardy and can tolerate freezing of up to two-thirds of their body water. For 25 years, Jon Costanzo and Richard Lee, Jr, both from Miami University, USA, have been studying these wood frogs, which are native to Alaska, Canada and the northern USA, to unravel their secrets. Costanzo explains that one well-known technique in the Ohioan population is to stock up on cryoprotectant solutes: 'When you load your blood with solutes, whether it's glucose, urea, glycerol or whatever, you drive down the [blood's] freezing point. Therefore, at any given temperature, you reduce the amount of ice that forms.' So, even when temperatures drop to -5°C in Ohio, some water remains unfrozen. In Alaska, however, temperatures go down to -30°C during winter and so Costanzo and Lee wondered whether Alaskan frogs have some additional tricks to aid their survival.
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