A test of alternate models for increased tissue nitrogen isotope ratios during fasting in hibernating arctic ground squirrels

Lee, Trixie N.; Buck, C. Loren; Barnes, Brian M.; O’Brien, Diane M.

doi:10.1242/jeb.068528

Cited by 50 publications

(62 citation statements)

References 58 publications

(78 reference statements)

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“…However, higher δ 15 N values in the baleen of EC-WG whales occurred in the most recently grown baleen in summer, when they are known to feed heavily on zooplankton blooms. Recent studies such as Aguilar et al (2014) and Matthews and Ferguson (2015) observed a similar pattern of 15 N enrichment in summer in baleen plates of a larger sample of EC-WG bowhead whales and in fin whales (Balaenoptera physalus), respectively, that are also contrary to the proposal that fasting leads to higher δ 15 N values (e.g., Best and Schell 1996;Cherel et al 2005;Lee et al 2012). It is more likely that summer feeding in regions with different baseline values or different types of prey led to depletion in 15 N (e.g., Aguilar et al 2014).…”

Section: Seasonal Cycling: Bcb and Ec-wg Individual Whalesmentioning

confidence: 71%

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

et al. 2018

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Previous studies have demonstrated that the analysis of biogeochemical tracers along baleen can provide seasonal, annual, and longer term insights into whale movements, habitat use, diet, and ecosystem processes. We measured the mercury (Hg) concentration and stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope compositions along baleen plates of bowhead whales (Balaena mysticetus) harvested between 1988 and 1996 from the Bering-Chukchi-Beaufort (BCB) and the Eastern CanadaWest Greenland (EC-WG) populations. These measurements were compared among individuals and between populations to assess seasonal cycling and to determine if bowhead whales forage year-round rather than fasting in winter. Individuals from the BCB population had synchronous cycles with higher Hg concentrations and lower δ 13 C values in summer and lower Hg concentrations and higher δ 13 C values in winter. EC-WG individuals also had synchronized periodic variations with peak values in isotopic ratios during summer. These results reflect an annual cycle of seasonal migration between distinct food webs in both populations. Spring and fall feeding activity was indicated in the intra-annual Hg and δ 13 C cycles along the baleen plates of all whales in our study. These shorter periods, spanning about half the annual growth, have not been previously described in the baleen of these populations, and are consistent with separate foraging areas along the migration routes. The results of this study provide further support for year-round foraging in a species previously thought to fast during winter. Future monitoring of seasonal foraging patterns in baleen would help to determine whether bowhead whales alter their foraging patterns in response to shifts in zooplankton community availability, composition, and phenology.

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Section: Seasonal Cycling: Bcb and Ec-wg Individual Whalesmentioning

confidence: 71%

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

et al. 2018

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“…Urea and Ca 2+ are of particular interest due to the unique changes in the animal's regulation of the urea cycle and Ca 2+ signaling, which occur during mammalian hibernation (Chilian and Tollefson 1976;Wang et al , 2002Stenvinkel et al 2013;Lee et al 2012;Epperson et al 2011). The addition of 5 and 100 mM of urea seemed to have no effect on the binding of NFATc1, c3, or c4 to DNA, with Fig.…”

Section: Effect Of Camentioning

confidence: 99%

Regulation of gene expression by NFAT transcription factors in hibernating ground squirrels is dependent on the cellular environment

Zhang

2016

Cell Stress and Chaperones

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Calcineurin is a calmodulin-stimulated phosphatase that regulates the nuclear translocation of nuclear factor of activated T cell (NFAT) c1-4 through dephosphorylation. We believe that this mechanism plays various roles in the remodeling and maintenance of Ictidomys tridecemlineatus skeletal muscle. During hibernation, bouts of torpor and arousal take place, and squirrels do not lose muscle mass despite being inactive. Protein expression of Ca 2+ signaling proteins were studied using immunoblotting. A DNA-protein interaction ELISA technique was created to test the binding of NFATs in the nucleus to DNA probes containing the NFAT response element under environmental conditions reflective of those during hibernation. Calcineurin protein levels increased by 3.08-fold during torpor (compared to euthermic control), whereas calpain1 levels also rose by 3.66-fold during torpor. Calmodulin levels were elevated upon entering torpor. NFATc4 binding to DNA showed a 1.4-fold increase during torpor, and we found that this binding was further enhanced when 600 nM of Ca 2+ was supplemented. We also found that decreasing the temperature of ELISAs resulted in progressive decreases in the binding of NFATs c1, c3, and c4 to DNA. In summary, calmodulin and calpain1 appear to activate calcineurin and NFATc4 during torpor. NFAT binding to target promoters is affected by intranuclear [Ca 2+ ] and environmental temperatures. Therefore, Ca 2+ signaling and temperature changes play key roles in regulation of the NFAT-calcineurin pathway in skeletal muscle of hibernating 13-lined ground squirrels over the torpor-arousal cycle, and they may contribute to the avoidance of disuse-induced muscle atrophy that occurs naturally in these animals.

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“…There have been few attempts to explore the effects of metabolic mechanisms within a single species despite the obvious advantage that this has on controlling metabolic variability. In this study, we explore the effect of nutritional stress on Δ (Deschner et al 2012;Lee et al 2012;Hobson and Quirk 2014;BenDavid et al 2012), there is still a need for further experiments on a greater number of species and with varying dietary restrictions.…”

Section: Introductionmentioning

confidence: 99%

The influence of food quantity on carbon and nitrogen stable isotope values in southern African spiny mice (Acomys spinosissimus)

et al. 2015

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Stable isotope analysis is frequently applied as a tool to examine dietary patterns in animals. However, some of the underlying assumptions associated with using this approach are increasingly being questioned. We carried out a controlled diet experiment on the southern African spiny mouse (Acomys spinosissimus Peters, 1852) to test a number of aspects relating to these assumptions and also examine the hypothesis that stable isotopes, especially δ 15 N, can be used to provide evidence of nutritional stress. We compared the δ 13 C and δ 15 N values of livers and blood from animals that were fed ad libitum with animals undergoing a 10% reduction in food supply. Food-restricted animals showed no significant difference in δ 15 N; however, δ 13 C values of both liver and blood were depleted. Restricted animals also had a significantly lower C:N ratio. We examined the role of lipids and found following lipid extraction that both livers and lipids still showed the same separation in carbon values. Tissue-diet discrimination values were also calculated and found to be higher for both Δ 13 C and Δ 15 N compared with other mice species. Empirical values for discrimination rates were then compared with values calculated using an alternative method based on employing generic values and were found to be dissimilar, suggesting the use of generic values are not always appropriate. Our results highlight the need for greater understanding of the assumptions associated with using stable isotope analysis to examine diet and we suggest that studying a single species under captive conditions presents an ideal method to begin to test these hypotheses.

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A test of alternate models for increased tissue nitrogen isotope ratios during fasting in hibernating arctic ground squirrels

Abstract: SUMMARYWe describe two models explaining the increase in tissue nitrogen isotope ratios ( Supplementary material available online at

Cited by 50 publications

References 58 publications

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

Regulation of gene expression by NFAT transcription factors in hibernating ground squirrels is dependent on the cellular environment

The influence of food quantity on carbon and nitrogen stable isotope values in southern African spiny mice (Acomys spinosissimus)

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