Survival of Frogs in Low Temperature

SUMMARYThe physiological responses supporting freeze tolerance in anurans are well known, but the evolution of this trait remains little studied. This is the first common-garden study of geographic variation in cryoprotective responses to freezing and the degree of freeze tolerance. We studied the gray treefrogs(Hyla versicolor and H. chrysoscelis) from sympatric sites in Minnesota, Indiana and Missouri. Patterns in the literature suggest that northern frogs produce more cryoprotectants upon freezing, but we found no geographic variation in cryoprotective responses or degree of freeze tolerance. The concentration of glucose produced upon freezing was higher than previously reported for this species (liver: 475 μmol g–1dry mass). Unfrozen frogs had high levels of glycerol (liver: approx. 150μmol g–1 dry mass), and did not produce more upon freezing. Liver glycogen content (concentration multiplied by liver mass) was highest in frogs from Minnesota and Missouri, and was stored in preference to lipids in Minnesota frogs, possibly to provide energy for the longer northern winters. Minnesota frogs accumulated more ice (53.4±1.8%) after freezing to–2.5°C than Indiana frogs (45.5±3.3%). The two species differed in body size but not in any of the physiological parameters measured. We conclude that these populations show no adaptive variation in freeze tolerance and that comparing published studies may be misleading because of different acclimation and feeding regimes.

Section: Table·2 Survival Of Gray Treefrogs Of Both Species and Fromsupporting

confidence: 79%

Geographic variation in energy storage and physiological responses to freezing in the gray treefrogsHyla versicolorandH. chrysoscelis

Irwin

Lee

2003

“…Freeze-tolerant frogs of cool-temperate regions commonly experience thermal minima of -5 or -7°C within their shallow, terrestrial hibernacula (MacArthur and Dandy, 1982;Schmid, 1982), although lower temperatures and longer chilling excursions probably affect populations at higher latitudes. Temperatures in the winter microenvironment occupied by R. sylvatica in Interior Alaska are indeed more severe (Middle and Barnes, 2000;Barnes et al, 1996) and presumably demand a commensurately greater tolerance to freezing.…”

Section: Extreme Freeze Tolerancementioning

confidence: 99%

Hibernation physiology, freezing adaptation and extreme freeze tolerance in a northern population of the wood frog

Costanzo

Amaral

Rosendale

et al. 2013

117

133

SUMMARYWe 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) 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) 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.

“…Long known in arthropods and other invertebrates, it was first reported in vertebrates only some 30years ago (Schmid, 1982). It is currently known in anuran and urodele amphibians, both suborders of (Costanzo et al, 2000b).…”

Section: Freeze Tolerance As a Survival Strategymentioning

confidence: 99%

“…Thermal conditions in winter refugia vary markedly, the intensity and frequency of chilling excursions increasing with altitude and latitude, and decreasing with any insulation afforded by the microenvironment. In temperate regions, frogs overwintering on the forest floor may encounter minima of −5 or −7°C (MacArthur and Dandy, 1982;Schmid, 1982), although more severe chilling can occur in northerly regions. Temperatures ranging between −1 and −4°C were recorded in grass tussocks harboring European common lizards, Lacerta vivipara, during particularly cold periods with little snow cover (Grenot et al, 2000).…”

Section: Winter Thermal Environmentmentioning

confidence: 99%

“…Seminal studies of freeze tolerance in woodland frogs have documented their efficacious system for copiously mobilizing glucose or glycerol in direct response to corporal freezing (Schmid, 1982;Storey and Storey, 1988). Cryoprotectant is chiefly derived from glycogen that accumulates in liver, representing up to 20% of organ mass, during late summer and autumn.…”

Section: Cryoprotective Solutesmentioning

confidence: 99%

See 1 more Smart Citation

Avoidance and tolerance of freezing in ectothermic vertebrates

Costanzo

Lee

2013

113

111

Ectothermic vertebrates have successfully colonized virtually every available ecological niche on Earth, some thriving in seasonally or continuously cold habitats at high latitudes and altitudes. In this commentary we briefly discuss adaptations of these animals to survive exposure to subzero temperatures and, in certain cases, the freezing of their body fluids.Excepting certain polar fishes, which swim in ice-laden waters, most aquatic species occupy habitats that are relatively warm. Accordingly, we here focus on terrestrial species whose body temperature (T b ) may fall appreciably below the equilibrium freezing/melting point (T Feq ) of their body fluids. Some of the key tenets of cold hardiness are best illustrated from invertebrates, which are more extensively researched than higher taxa. However, we liberally reference two of the best-studied and most cold-hardy vertebrates. The wood frog (Rana sylvatica), the most northerly distributed of North American amphibians, occurs within the Arctic Circle. Throughout its range, this species overwinters beneath forest duff where it encounters subzero cold but nevertheless survives the freezing of its tissues. The painted turtle (Chrysemys picta) is a cold-adapted reptile that ranges to within 7° latitude of the Arctic Circle. Hatchlings of this species commonly overwinter within the natal nest, only 5-10cm below the ground surface, but can survive chilling to temperatures as low as −4°C in the frozen state or −15°C by avoiding freezing. Winter thermal environmentAmong cold-hardy organisms, capacity for cold tolerance is tuned to the temperatures and exposure durations that a given species encounters within its habitat (Addo-Bediako et al., 2000). Thermal conditions in winter refugia vary markedly, the intensity and frequency of chilling excursions increasing with altitude and latitude, and decreasing with any insulation afforded by the microenvironment. In temperate regions, frogs overwintering on the forest floor may encounter minima of −5 or −7°C (MacArthur and Dandy, 1982;Schmid, 1982), although more severe chilling can occur in northerly regions. Temperatures ranging between −1 and −4°C were recorded in grass tussocks harboring European common lizards, Lacerta vivipara, during particularly cold periods with little snow cover (Grenot et al., 2000). Where snow cover is routinely sparse and winters severe, temperatures can be, but are not necessarily, extreme. At a given study site, thermal minima within C. picta nests can vary by 10°C or more, reflecting differences in nest depth, slope, aspect, patchiness of snow cover, and other physiognomic factors (Costanzo et al., 2004;Weisrock and Janzen, 1999). A common but erroneous perception is that all hibernators must endure a single, winter-long bout of extreme cold. The more accurate scenario, especially for animals using wellinsulated refugia, is for the temperature to hover near 0°C for extended periods that may (or may not) be punctuated by brief (i.e. hours to days) excursions to slightly lower temperatures be...