title: Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance.
abstract: We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring. We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs. We also recorded the behavior of wood frogs preparing to freeze in artificial hibernacula, and tissue glucose concentrations in captive wood frogs frozen in the laboratory to -2.5°C. Wood frogs in natural hibernacula remained frozen for 193 ± 11 consecutive days and experienced average (October-May) temperatures of -6.3°C and average minimum temperatures of -14.6 ± 2.8°C (range -8.9 to -18.1°C) with 100% survival (N=18). Mean glucose concentrations were 13-fold higher in muscle, 10-fold higher in heart and 3.3-fold higher in liver in naturally freezing compared with laboratory frozen frogs. Antifreeze glycolipid was present in extracts from muscle and internal organs, but not skin, of frozen frogs. Wood frogs in Interior Alaska survive freezing to extreme limits and durations compared with those described in animals collected in southern Canada or the Midwestern United States. We hypothesize that this enhancement of freeze tolerance in Alaskan wood frogs is due to higher cryoprotectant levels that are produced by repeated freezing and thawing cycles experienced under natural conditions during early autumn.
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775, USA djlarson@alaska.edu bmbarnes@alaska.edu.
authors.forename: Don J
authors.initials: DJ
authors.lastname: Larson
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
authors.forename: Luke
authors.initials: L
authors.lastname: Middle
authors.affiliation: Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Vu
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Wenhui
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Anthony S
authors.initials: AS
authors.lastname: Serianni
authors.affiliation: Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: John
authors.initials: J
authors.lastname: Duman
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA djlarson@alaska.edu bmbarnes@alaska.edu.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Barnes
mesh_terms: D000222:Adaptation, Physiological; D000413:Alaska; D000818:Animals; D003451:Cryoprotective Agents / Q000378:metabolism*; D005260:Female; D005615:Freezing; D006017:Glycolipids / Q000378:metabolism*; D006605:Hibernation; D008297:Male; D011898:Ranidae / Q000502:physiology*; D012621:Seasons
chemical_list: D003451:Cryoprotective Agents; D006017:Glycolipids
keywords: Antifreeze glycolipid; Cryoprotectant; Freeze tolerance; Wood frog