title: Hibernation physiology, freezing adaptation and extreme freeze tolerance in a northern population of the wood frog.
abstract: We investigated hibernation physiology and freeze tolerance in a population of the wood frog, Rana sylvatica, indigenous to Interior Alaska, USA, near the northernmost limit of the species' range. Winter acclimatization responses included a 233% increase in the hepatic glycogen depot that was subsidized by fat body and skeletal muscle catabolism, and a rise in plasma osmolality that reflected accrual of urea (to 106±10 μmol ml(-1)) and an unidentified solute (to ~73 μmol ml(-1)). In contrast, frogs from a cool-temperate population (southern Ohio, USA) amassed much less glycogen, had a lower uremia (28±5 μmol ml(-1)) and apparently lacked the unidentified solute. Alaskan frogs survived freezing at temperatures as low as -16°C, some 10-13°C below those tolerated by southern conspecifics, and endured a 2-month bout of freezing at -4°C. The profound freeze tolerance is presumably due to their high levels of organic osmolytes and bound water, which limits ice formation. Adaptive responses to freezing (-2.5°C for 48 h) and subsequent thawing (4°C) included synthesis of the cryoprotectants urea and glucose, and dehydration of certain tissues. Alaskan frogs differed from Ohioan frogs in retaining a substantial reserve capacity for glucose synthesis, accumulating high levels of cryoprotectants in brain tissue, and remaining hyperglycemic long after thawing. The northern phenotype also incurred less stress during freezing/thawing, as indicated by limited cryohemolysis and lactate accumulation. Post-glacial colonization of high latitudes by R. sylvatica required a substantial increase in freeze tolerance that was at least partly achieved by enhancing their cryoprotectant system.
authors: Department of Zoology, Miami University, Oxford, OH 45056, USA. costanjp@miamioh.edu
authors: Jon P
authors: JP
authors: Costanzo
authors: M Clara F
authors: MC
authors: do Amaral
authors: Andrew J
authors: AJ
authors: Rosendale
authors: Richard E
authors: RE
authors: Lee
mesh_terms: D000222:Adaptation, Physiological; D000413:Alaska; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005615:Freezing; D005843:Geography; D006003:Glycogen / Q000378:metabolism; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006605:Hibernation / Q000502:physiology*; D007773:Lactates / Q000097:blood; D008099:Liver / Q000378:metabolism; D009820:Ohio; D009928:Organ Specificity; D011898:Ranidae / Q000097:blood / Q000502:physiology*; D012621:Seasons; D013312:Stress, Physiological; D013997:Time Factors; D014508:Urea / Q000097:blood / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D006454:Hemoglobins; D007773:Lactates; D014508:Urea; D006003:Glycogen
keywords: Rana sylvatica; anuran; cryoprotectant; ecogeography; freeze tolerance