Meeting Abstract
The Rocky Mountain Tailed Frog, Ascaphus montanus is a cryophile that is associated with permanent mountain streams in the northwestern United States and Canada. Adults overwinter in these cold, fast moving streams, which requires surviving extended bouts of subzero temperatures. The purpose of this study was to determine if these frogs can tolerate winter conditions found in mountain streams by either surviving internal ice formation or avoiding freezing by resisting ice inoculation and supercooling. Winter acclimated frogs cooled from 2°C at 0.2°C h-1 had relatively low supercooling points compared to other frog species (-5.0 ± 0.1°C;n=3). To test their ability to remain supercooled and/or resist inoculative freezing, two additional groups were cooled at the above rate until reaching and being held at -1°C. Frogs maintained at -1°C in the absence of ice were able to maintain a supercooled state prior to freezing for considerably longer than most other freeze tolerant species of frogs (73 ± 22 h; n=4). Similar to other frogs, A. montanus did not resist inoculative freezing well. Frogs cooled to and maintained at -1°C froze within 30 minutes (16.1 ± 4.6 min; n=4), following addition of a 500mg piece of ice to their skin. After the last frog froze in the supercooling point determination trial or after being held at -1°C for seven days, all frogs were warmed at 0.2°C h-1 until reaching 2°C prior to assessing survival. No frogs survived the supercooling point trials or after being frozen by ice inoculation. However, two of the four frogs that were held at -1°C in the absence of ice survived supercooling for ~2 days followed by being frozen for ~5 days. In sum, A. montanus may be able to survive the high sub-zero temperatures found in montane streams during winter by either supercooling and/or surviving mild freezing.
