Gluconeogenesis in arctic ground squirrels between periods of hibernation

1975 ◽  
Vol 228 (1) ◽  
pp. 325-330 ◽  
Author(s):  
W Galster ◽  
PR Morrison
Keyword(s):  
Energy Source ◽  
Fatty Acid ◽  
Protein Metabolism ◽  
Ground Squirrel ◽  
Ammonia Nitrogen ◽  
Ground Squirrels ◽  
The Arctic ◽  
Major Energy Source ◽  
Arctic Ground Squirrels ◽  
Gluconeogenic Substrate

The hibernation season in the arctic ground squirrel (Citellus undulatus) is broken into 8- to 18- day cycles by short homeothermal periods during which the carboydrate reserves depleted during hibernation are replenished. This study follows a number of metabolities in tissues and body fluids to assess the sources for reconstitution of the glucose reserves: lactate, urea, ammonia, free fatty acid, glycerol, triglyceride, and glucose in plasma; glycogen in liver and muscle; and urea and ammonia nitrogen in urine. Fat is the major energy source during both homeothermal and heterothermal periods, the contribution from glucose being limited to glycolysis. Reconstitution of glycogen is accomplished prior to reentry through maximal use of substrates from all sources including glycolysis, fat, and protein metabolism. Of the new gluconeogenic substrate, one-fourth is supplied from protein and three-fourths from fat.

scholarly journals Hibernation strategies and patterns in sympatric arctic species, the Alaska marmot and the arctic ground squirrel

2015 ◽  
Vol 97 (1) ◽  
pp. 135-144 ◽  
Author(s):  
Trixie N. Lee ◽  
Franziska Kohl ◽  
C. Loren Buck ◽  
Brian M. Barnes
Keyword(s):  
Ground Squirrel ◽  
Core Body Temperature ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Slow Cooling ◽  
Ambient Temperatures ◽  
The Difference ◽  
Arctic Ground Squirrels ◽  
Core Body

Abstract We compared patterns of core body temperature ( Tb ) change, including inter-individual synchrony, in 2 free-living arctic hibernators that differ in size and sociality, the Alaska marmot ( Marmota broweri ) and the arctic ground squirrel ( Urocitellus parryii ). We report overwinter Tb changes from 3 to 4 marmots from the same hibernaculum in each of 3 years and from 7 ground squirrels that hibernated at 2 nearby burrow sites in 1 year. Very close synchrony in the timing of torpor and arousal cycles in Alaska marmots indicates social hibernation and thermoregulation, while lack of synchrony in arctic ground squirrels further confirms solitary hibernation. The mean duration between the first and last marmot measured within the group to initiate an arousal was 3.7±2.5h and to recool to 30°C during torpor entrance was 5.7±3.7h. The minimum Tb recorded in marmots was 0.6°C and in ground squirrels was −2.0°C. Marmots entering torpor displayed an interrupted pattern of Tb change defined by 2 distinct rates of cooling, early and late during entry, that differed by 21-fold. Ground squirrels cooled in a continuous pattern, initially 3-fold slower than marmots during rapid cooling but 4-fold faster during slow cooling. Both species must minimize energy expenditure to survive long arctic winters; our results suggest that Alaska marmots do this through social thermoregulation, while arctic ground squirrels decrease Tb below freezing to minimize the difference between body and ambient temperatures.

Seasonal changes in body composition of the arctic ground squirrel, Citellus undulatus

1976 ◽  
Vol 54 (1) ◽  
pp. 74-78 ◽  
Author(s):  
William Galster ◽  
Peter Morrison
Keyword(s):  
Seasonal Changes ◽  
Ground Squirrel ◽  
Significant Loss ◽  
Ground Squirrels ◽  
The Arctic ◽  
Average Weight ◽  
Active Season ◽  
Loss Of Weight ◽  
Glucose Synthesis ◽  
Arctic Ground Squirrels

The depletion or accumulation of body reserves is followed in terms of the weight and proportion of lipid, protein, water, and minerals in arctic ground squirrels during the entry, deep, and emergent phases of the hibernation season and after the reproductive phase of the active season. Average weight increased slowly through the summer, from a minimum of 346 g, until mid-August when 190 g accumulated in 3 weeks to be used subsequently during the 220-day hibernation season beginning in mid-September. During hibernation, the 325-g loss in weight represents 62% lipid, 26% water, 9% protein, and 2% mineral. Fat in lipid provides most of the energy but insufficient amounts of carbon for glucose synthesis during hibernation. However, protein provides an adequate gluconeogenic reserve. Significant loss of mineral indicates that skeletal reserves of calcium are important during hibernation. After hibernation, continued loss of weight by females indicates further utilization of reserves during gestation and nursing.

scholarly journals Effects of Season and Host Physiological State on the Diversity, Density, and Activity of the Arctic Ground Squirrel Cecal Microbiota

2014 ◽  
Vol 80 (18) ◽  
pp. 5611-5622 ◽  
Author(s):  
Timothy J. Stevenson ◽  
Khrystyne N. Duddleston ◽  
C. Loren Buck
Keyword(s):  
Seasonal Changes ◽  
Ground Squirrel ◽  
Short Chain Fatty Acid ◽  
Chain Fatty Acid ◽  
Ground Squirrels ◽  
Short Chain ◽  
The Arctic ◽  
Content Type ◽  
Cecal Microbiota ◽  
Arctic Ground Squirrels

ABSTRACTWe examined the seasonal changes of the cecal microbiota of captive arctic ground squirrels (Urocitellus parryii) by measuring microbial diversity and composition, total bacterial density and viability, and short-chain fatty acid concentrations at four sample periods (summer, torpor, interbout arousal, and posthibernation). Abundance ofFirmicuteswas lower, whereas abundances ofBacteroidetes,Verrucomicrobia, andProteobacteriawere higher during torpor and interbout arousal than in summer. Bacterial densities and percentages of live bacteria were significantly higher in summer than during torpor and interbout arousal. Likewise, total short-chain fatty acid concentrations were significantly greater during summer than during torpor and interbout arousal. Concentrations of individual short-chain fatty acids varied across sample periods, with butyrate concentrations higher and acetate concentrations lower during summer than at all other sample periods. Characteristics of the gut community posthibernation were more similar to those during torpor and interbout arousal than to those during summer. However, higher abundances of the generaBacteroidesandAkkermansiaoccurred during posthibernation than during interbout arousal and torpor. Collectively, our results clearly demonstrate that seasonal changes in physiology associated with hibernation and activity affect the gut microbial community in the arctic ground squirrel. Importantly, similarities between the gut microbiota of arctic ground squirrels and thirteen-lined ground squirrels suggest the potential for a core microbiota during hibernation.

Patterns of hibernation in the arctic ground squirrel

1975 ◽  
Vol 53 (9) ◽  
pp. 1345-1355 ◽  
Author(s):  
Peter Morrison ◽  
William Galster
Keyword(s):  
Annual Cycle ◽  
Ground Squirrel ◽  
Ground Squirrels ◽  
The Arctic ◽  
Light Cycle ◽  
Arctic Ground Squirrel ◽  
Active Season ◽  
Cyclic Patterns ◽  
Arctic Ground Squirrels ◽  
Normal Light

Cyclic patterns were defined in subspecies of arctic ground squirrels (Citellus undulatus) from the Brooks and Alaskan Ranges. In the annual cycle a heterothermal (hibernation) season with entry, maintenance, and emergence stages was distinguished from a homeothermal (active) season with reproductive, recovery/growth, maintenance, and fattening stages. The heterothermal season consisted of a series of short hibernation cycles in which heterothermal (hibernation) periods with reentry, refractory, and irritable phases were distinguished from homeothermal (active) periods with arousal, maintenance, and preparation phases. Squirrels in which exposure to darkness at 5 °C was delayed (Nov. vs. Sept.) showed a lesser response but emerged synchronously with the normal group. Entry was attenuated with a normal light cycle at 5 °C (8 vs. 3 weeks). Juveniles showed a 2- to 4-week delay in entry as compared to adults.

Temperature and the Regulation of Enzyme Activity in the Hibernator. Isoenzymes of Liver Pyruvate Kinase from the Hibernating and Non-hibernating Arctic Ground Squirrel

1974 ◽  
Vol 52 (10) ◽  
pp. 894-902 ◽  
Author(s):  
Hans W. Behrisch
Keyword(s):  
Molecular Weight ◽  
Pyruvate Kinase ◽  
Wide Temperature Range ◽  
Ground Squirrel ◽  
Energy Charge ◽  
High Energy ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Temperature Range

Liver of the hibernating (H) Arctic ground squirrel (Citellus undulatus) contains a single species of pyruvate kinase (PyK) that is distinct from the single isoenzyme of pyK observed in the non-hibernating (NH) ground squirrel, which has been previously described (Behrisch &Johnson (1974) Can. J. Biochem. 52, 547–559). The H-PyK has a pI value of 5.7 and a molecular weight of 241 000 – 243 000. Affinity of the H-PyK for the substrates phosphoenolpyruvate (PEP) and ADP is not affected by changing temperature. It is argued that this stability of the apparent Km's for substrate over a wide temperature range permits the hibernator to take advantage of the Q10 effect in maintaining a low rate of the PyK reaction. Similarly, affinity of H-PyK for the allosteric activator fructose-1,6-phosphate (FDP) and the inhibitor ATP is also conspicuously independent of temperature, suggesting a fine stoichiometry in the relative concentrations of the regulatory ligands in control of H-PyK over a wide temperature range. Further, affinity of H-PyK for the inhibitor ATP is about three- to fourfold lower than that of the NH-PyK, a condition that would favor the maintenance of a high energy charge in the hibernating liver cell. ATP apparently inhibits PyK by causing a dissociation of the enzyme molecule into two "halves" of about 110 000 molecular weight each. This dissociation is offset and reversed by FDP. Removal of the ATP by dialysis does not of itself result in a reassociation of the PyK "halves"; FDP and/or the substrates are required for the two subunits of PyK to reassociate. As the apparent Ki of H-PyK for ATP is higher than that of NH-PyK, substantially higher concentrations of ATP are required to effect the dissociation of H-PyK. Similarly, elevated concentrations of FDP are required to offset the ATP-caused dissociation of the H-PyK.Hibernating Arctic ground squirrels that are preparing to emerge finally from the hibernating state already possess substantial activities of the NH-PyK isoenzyme. This suggests that the animal "anticipates" its transition from one metabolic state from another. On the basis of these data a formal mechanism is proposed for the regulation of liver PyK in the Arctic ground squirrel in both the non-hibernating and hibernating states.

Ketone body metabolism in a ground squirrel during hibernation and fasting

1985 ◽  
Vol 249 (4) ◽  
pp. R462-R470 ◽  
Author(s):  
B. L. Krilowicz
Keyword(s):  
Energy Source ◽  
Glucose Uptake ◽  
Ground Squirrel ◽  
Ketone Body ◽  
Glucose Utilization ◽  
Ground Squirrels ◽  
Body Protein ◽  
Muscle Tissues ◽  
Spermophilus Beldingi

Hibernating Belding's ground squirrels (Spermophilus beldingi) are ketotic relative to fed nonhibernators. Muscles from torpid individuals, when incubated in media containing physiological concentrations of glucose and ketone, show reduced uptake of glucose in the presence of ketone. The magnitude of the reduction is dependent on ketone concentration and reaches 60% in heart and 100% in pectoralis at 1.4 mM ketone. Fasted squirrels are also ketotic. However, ketone does not reduce glucose uptake in muscles from fed or fasted animals. Glucose utilization by muscles decreases during a long-term fast, but the reduction is independent of ketone. Thus both a long-term fast and hibernation lead to changes in muscle tissues that decrease their reliance on glucose as an energy source. Ketosis leads to glucose sparing during hibernation, whereas muscle glucose utilization is decreased independently of ketone during a fast. The glucose sparing achieved in both hibernation and fasting leads to conservation of body protein, the major source of gluconeogenic precursors in fasting mammals.

Effects of food and predators on the home-range sizes of Arctic ground squirrel (Spermophilus parryii)

1998 ◽  
Vol 76 (3) ◽  
pp. 592-596 ◽  
Author(s):  
Anne H Hubbs ◽  
Rudy Boonstra
Keyword(s):  
Home Range ◽  
Ground Squirrel ◽  
Large Scale ◽  
Yukon Territory ◽  
Ground Squirrels ◽  
Home Ranges ◽  
Spermophilus Parryii ◽  
Mammalian Predators ◽  
Core Areas ◽  
Arctic Ground Squirrels

We used radiotelemetry to study the effects of food addition and predator reduction on the home-range sizes of adult Arctic ground squirrels (Spermophilus parryii) on large-scale experimental grids in the boreal forest of the southwestern Yukon Territory. Home ranges were 2-7 times smaller on food-supplemented grids than on nonsupplemented grids, regardless of whether large mammalian predators were present. Similarly, core areas (where 50% of activities occur) were 8-11 times smaller on food-supplemented grids. Food availability rather than predator presence primarily determined the sizes of home ranges and core areas of Arctic ground squirrels.

scholarly journals Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon

2015 ◽  
Vol 42 (2) ◽  
pp. 176 ◽  
Author(s):  
Jeffery R. Werner ◽  
Charles J. Krebs ◽  
Scott A. Donker ◽  
Rudy Boonstra ◽  
Michael J. Sheriff
Keyword(s):  
Boreal Forest ◽  
Ground Squirrel ◽  
Boreal Forests ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Forest Zone ◽  
Winter Climate ◽  
Population Collapse ◽  
Predator Pit

Context The arctic ground squirrel (Urocitellus parryii) comprised 17% of the biomass of herbivores in the Yukon boreal forest during the summer months from 1987 to 1996 and was responsible for 23% of the energy flow at the herbivore level. By 2000, ground squirrel populations in this region collapsed to nearly zero and have remained there. Aims We summarise the population monitoring (since 1975) and recent experimental work that has been done on this key herbivore in the Kluane area of the southern Yukon to test one mechanistic hypothesis as the possible explanation for this population collapse and subsequent lack of recovery: predation. Methods Ground squirrels are the preferred summer prey of bird and mammal predators when snowshoe hare (Lepus americanus) populations are declining. We used translocations into formerly occupied habitat and radiotelemetry to determine movements and causes of death from 2009 to 2014. We surveyed 158 sites between 2008 and 2013 to measure the disappearance of colonies in alpine and forest habitats over 25 000 km2. Key results Ground squirrels from 2000 to 2013 comprised a small fraction of the herbivore biomass in the boreal forest zone, down from 17% earlier. Most forest populations (~95%) are currently extinct, whereas just over half (65%) of low-elevation meadow populations are locally extinct. One hypothesis is that ground squirrels in the forest have been driven into a predator pit from which they cannot recover. They remain abundant in alpine tundra (93% occupancy rate) and around airport runways and human habitations (97% occupancy), but there is no apparent dispersal from alpine areas down into the boreal forest. Conclusion The predator pit hypothesis is a likely explanation for the initial collapse and sustained decline in population size from 2000 to 2013. Recent attenuation of the hare cycle and milder winter climate have allowed shrubs to expand throughout the forest, thereby reducing visibility and increasing predation risk. This conclusion will be tested in further research using reintroductions to formerly occupied sites. Implication If the loss of this herbivore from the boreal forest is not reversed, predator pressure on the other major herbivores of the montane forest zone is likely to change significantly.

scholarly journals Cytoprotection by a naturally occurring variant of ATP5G1 in Arctic ground squirrels

2020 ◽  
Author(s):  
Neel S. Singhal ◽  
Meirong Bai ◽  
Evan M. Lee ◽  
Shuo Luo ◽  
Kayleigh R. Cook ◽  
...  
Keyword(s):  
Anaerobic Bacteria ◽  
Ectopic Expression ◽  
Metabolic Stress ◽  
Ground Squirrels ◽  
The Arctic ◽  
Cellular Mechanisms ◽  
Base Editing ◽  
Naturally Occurring ◽  
Mitochondrial Atp Synthase ◽  
Arctic Ground Squirrels

AbstractMany organisms, from anaerobic bacteria to hibernating ground squirrels, have evolved mechanisms to tolerate severe hypoxia or ischemia. In particular, the arctic ground squirrel (AGS) has been shown to be highly resilient to ischemic and reperfusion injuries, demonstrating an ability to withstand metabolic stress under hibernation conditions. Although physiological adaptations are critical to ischemic tolerance in AGS, little is known about cellular mechanisms underlying intrinsic AGS cell tolerance to metabolic stressors. Through cell survival-based cDNA expression screens and comparative genomics, we have discovered that in AGS, a cytoprotective variant of ATP5G1 helps confer improved mitochondrial metabolism and cell resilience to metabolic stress. ATP5G1 encodes a proton-transporting subunit of the mitochondrial ATP synthase complex. Ectopic expression in mouse cells and CRISPR/Cas9 base editing of the endogenous AGS locus revealed causal roles of one AGS-specific amino acid substitution (leucine-32) in mediating the cytoprotective effects of AGS ATP5G1. We provide evidence that AGS ATP5G1 promotes cell resilience to stress by modulating mitochondrial morphological change and metabolic functions. Thus, our results identify a naturally occurring variant of ATP5G1 from a mammalian hibernator that causally contributes to intrinsic cytoprotection against metabolic stresses.

scholarly journals Daily body temperature rhythms persist under the midnight sun but are absent during hibernation in free-living arctic ground squirrels

2011 ◽  
Vol 8 (1) ◽  
pp. 31-34 ◽  
Author(s):  
Cory T. Williams ◽  
Brian M. Barnes ◽  
C. Loren Buck
Keyword(s):  
Body Temperature ◽  
Circadian Rhythms ◽  
Ground Squirrels ◽  
The Arctic ◽  
Constant Light ◽  
Polar Regions ◽  
Free Living ◽  
Active Season ◽  
Temperature Rhythms ◽  
Arctic Ground Squirrels

In indigenous arctic reindeer and ptarmigan, circadian rhythms are not expressed during the constant light of summer or constant dark of winter, and it has been hypothesized that a seasonal absence of circadian rhythms is common to all vertebrate residents of polar regions. Here, we show that, while free-living arctic ground squirrels do not express circadian rhythms during the heterothermic and pre-emergent euthermic intervals of hibernation, they display entrained daily rhythms of body temperature ( T b ) throughout their active season, which includes six weeks of constant sun. In winter, ground squirrels are arrhythmic and regulate core body temperatures to within ±0.2°C for up to 18 days during steady-state torpor. In spring, after the use of torpor ends, male but not female ground squirrels, resume euthermic levels of T b in their dark burrows but remain arrhythmic for up to 27 days. However, once activity on the surface begins, both sexes exhibit robust 24 h cycles of body temperature. We suggest that persistence of nycthemeral rhythms through the polar summer enables ground squirrels to minimize thermoregulatory costs. However, the environmental cues (zeitgebers) used to entrain rhythms during the constant light of the arctic summer in these semi-fossorial rodents are unknown.

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