CAN BOREAL COMMON FROG (RANA TEMPORARIA L.) SURVIVE IN FROST

Abstract

The first observations concerning the tolerance of vertebrate species to freezing were reported about fifteen years ago in America (Schmid 1982, Storey 1985) where four amphibian species were found to be able to endure freezing (even – 6°C– – 10°C). Since that discovery, many articles have been published on this topic (e.g. Franks 1985, Marchand 1987, Pegg & Karow 1988, Storey & Storey 1988, 1990, Storey 1990, Storey et al. 1996). One of the species that tolerates freezing is the wood frog (Rana sylvatica), whose relative in Finland is the common frog (Rana temporaria L.). Previously we suggested that in Finland, under severe winter conditions, the common frog generally survives if wintering in aquatic sites, and terrestrial wintering is successful only occasionally (Koskela & Pasanen 1974, Pasanen & Koskela 1980). However, at the end of the 1980s we observed that part of the frog population overwinter on land (Pasanen et al. 1993, 1994), and our observations during the winter of 1992–1993 suggested that the Finnish common frog manages to survive the winter on the ground (Pasanen & Sorjonen 1994). Nevertheless, we cannot say on the basis of these experiments if the frogs placed in the wintering boxes were in the frozen state or not. The aim of this study was to establish whether the common frog (Rana temporaria L.) can endure freezing and survive in frost. In the experiments, all frogs survived 24 hours at – 2°C, but a longer period at temperatures below 0°C caused death in three days. The glucose concentration in the liver after three days was about six times higher than the control level. Glycerol content in the liver was very low the whole time. The common frog is not as well adapted to freezing as the wood frog (Rana sylvatica) but can tolerate short periods of freezing temperature (less than three days).