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Hibernation is associated with long lifespan: on average, hibernating mammals live 15% longer than nonhibernators of equivalent mass. We investigated how survival varies with sex, season, and the deployment of biologgers in arctic ground squirrels (Urocitellus parryii (Richardson, 1825)), a widely distributed northern hibernator. The duration of hibernation in arctic ground squirrels differs markedly by sex: females hibernate 30% longer each year than males, a behavioural trait that could positively affect female survival. Additionally, males engage in aggressive territorial and food cache defense in spring and fall, which may decrease survival in this sex. From 13 years of mark-recapture data, we estimated apparent survival of arctic ground squirrels in Arctic Alaska (USA) using Cormack-Jolly-Seber models in program MARK. We found that females had higher annual survival ( Key words: survival, lifespan, hibernation, biologging, arctic ground squirrel, Cormack-Jolly-Seber modeling, demographics, Urocitellus parryii. L'hibernation est associee a la duree de vie : en moyenne, les mammiferes qui hibernent vivent 15 % plus longtemps que les mammiferes de masse semblable qui n'hibernent pas. Nous examinons les variations de la survie en fonction du sexe, de la saison et du deploiement de capteurs de parametres biologiques chez le spermophile arctique (Urocitellus parryii (Richardson, 1825)), un mammifere nordique hibernant caracterise par une vaste repartition geographique. La duree de l'hibernation des spermophiles arctiques differe considerablement selon le sexe : les femelles hibernant 30 % plus longtemps chaque annee que les males, un caractere comportemental qui pourrait avoir une incidence positive sur la survie des femelles. En outre, les males s'adonnent a la defense agressive de leur territoire et de leurs caches de nourriture au printemps et a l'automne, ce qui peut reduire la survie chez ce sexe. A la lumiere de 13 annees de donnees de marquagerecapture, nous estimons le taux de survie apparent de spermophiles arctiques en Alaska arctique (Etats-Unis) en utilisant des modeles de Cormack-Jolly-Seber dans le programme MARK. Nous constatons que les femelles ont un plus haut taux de survie annuel ([[^.[phi].sub..sup.nnuel] = 0,753 (l'intervalle de confiance (IC) de 95 % : 0,469, 0,913)) que les males ([[^.phi].sup.annual.sub.M] = 0,546 (IC de 95 % : 0,416, 0,670)) et une duree de vie maximum observee (10 ans) plus grande que celle des males (6 ans). Nous demontrons egalement que l'utilisation et l'implantation de capteurs de parametres biologiques n'a pas d'impact significatif sur la survie. La quantification de parametres demographiques de base des spermophiles arctiques a la lumiere de cette population bien etudiee illustre l'influence que peuvent avoir les variations selon le sexe de parametres associes a l'hibernation sur les differences de duree de vie des spermophiles arctiques males et etaie l'argument voulant que les appareils d'enregistrement de parametres biologiques soient securitaires. [Traduit par la Redaction] Mots-cles: survie, duree de vie, hibernation, enregistrement de parametres biologiques, spermophile arctique, modelisation Cormack-Jolly-Seber, demographie, Urocitellus parryii., Introduction Hibernation is a strategy used by diverse species of mammals to survive prolonged resource scarcity (Geiser 1998; Staples 2016) and is associated with long lifespan: Turbill et al. (2011) [...]

Seasonal affective disorder (SAD) is a recurrent depression triggered by exposure to short photoperiods, with a subset of patients reporting hypersomnia, increased appetite, and carbohydrate craving. Dysfunction of the microbiota – gut – brain axis is frequently associated with depressive disorders, but its role in SAD is unknown. Nile grass rats (Arvicanthis niloticus) are potentially useful for exploring the pathophysiology of SAD, as they are diurnal and have been found to exhibit anhedonia and affective-like behavior in response to short photoperiods. Further, given grass rats have been found to spontaneously develop metabolic syndrome, they may be particularly susceptible to environmental triggers of metabolic dysbiosis. We conducted a 2 × 2 factorial design experiment to test the effects of short photoperiod (4 h:20 h Light:Dark (LD) vs. neutral 12:12 LD), access to a high concentration (8%) sucrose solution, and the interaction between the two, on activity, sleep, liver steatosis, and the gut microbiome of grass rats. We found that animals on short photoperiods maintained robust diel rhythms and similar subjective day lengths as controls in neutral photoperiods but showed disrupted activity and sleep patterns (i.e. a return to sleep after an initial bout of activity that occurs ~ 13 h before lights off). We found no evidence that photoperiod influenced sucrose consumption. By the end of the experiment, some grass rats were overweight and exhibited signs of non-alcoholic fatty liver disease (NAFLD) with micro- and macro-steatosis. However, neither photoperiod nor access to sucrose solution significantly affected the degree of liver steatosis. The gut microbiome of grass rats varied substantially among individuals, but most variation was attributable to parental effects and the microbiome was unaffected by photoperiod or access to sucrose. Our study indicates short photoperiod leads to disrupted activity and sleep in grass rats but does not impact sucrose consumption or exacerbate metabolic dysbiosis and NAFLD. [ABSTRACT FROM AUTHOR]

Thyroid hormones (TH) are key regulators of metabolism that could play an important role in altering physiology and energy allocation across life-history stages. Here, we examine seasonal TH dynamics from 345 plasma samples collected from 134 free-living arctic ground squirrels (Urocitellus parryii (Richardson, 1825)) across three consecutive years (2014-2016). We also examine whether unbound levels of triiodothyronine (free [T.sub.3]) in plasma are correlated with total [T.sub.3] levels and total thyroxine ([T.sub.4]) levels, and whether fecal [T.sub.3] metabolite levels correlate with plasma TH levels. We found significant differences in plasma TH levels across stages of the annual cycle, but these differences were highly inconsistent across years. However, within a given time period, pregnant females had lower free [T.sub.3] levels compared with lactating females. We also found that although free [T.sub.3] was correlated with both total [T.sub.3] and total [T.sub.4] in plasma, fecal [T.sub.3] was not positively correlated with plasma TH levels. Given the lack of consistent differences across life-history stages, we suggest environmental heterogeneity may be the primary driver of TH dynamics, masking any potential endogenous seasonal rhythms in TH secretion. We urge caution in the use of fecal [T.sub.3] metabolites as a proxy for circulating levels and encourage further research to understand the observed discrepancy. Key words: Urocitellus parryii, arctic ground squirrel, fecal hormones, reproductive state, thyroid, thyroxine, triiodothyronine. Les hormones thyroidiennes (HT) sont des regulateurs cles du metabolisme qui pourraient jouer un important role dans la modulation de la physiologie et de l'allocation d'energie durant les differentes etapes du cycle de vie. Nous examinons la dynamique saisonniere des HT de 345 echantillons de plasma preleves de 134 spermophiles arctiques (Urocitellus parryii (Richardson, 1825)) vivant en liberte sur trois annees consecutives (2014-2016). Nous tentons aussi de determiner si les concentrations de triiodothyronine libre ([T.sub.3] libre) dans le plasma sont correlees aux concentrations totales de [T.sub.3] et aux concentrations totales de thyroxine ([T.sub.4]), et si les concentrations fecales de metabolites de [T.sub.3] sont correlees aux concentrations plasmiques des HT. Nous relevons des differences significatives des concentrations plasmiques des HT entre les differentes etapes du cycle annuel, mais ces differences sont fortement incoherentes d'une annee a l'autre. Cependant, sur une periode de temps donnee, les femelles gestantes presentent des concentrations de [T.sub.3] libre plus faibles que les femelles en lactation. Nous constatons egalement que, si la [T.sub.3] libre est correlee a la [T.sub.3] totale et a la [T.sub.4] totale dans le plasma, la [T.sub.3] fecale n'est pas positivement correlee aux concentrations plasmiques des HT. Au vu de l'absence de difference coherente entre les differentes etapes du cycle biologique, nous proposons que l'heterogeneitedumilieu pourrait etreleprincipal facteurdemodulationdeladynamique des HT, masquant tout rythme saisonnier endogene eventuel de la secretion des HT. Nous pronons la prudence dans l'utilisation de metabolites fecaux de la [T.sub.3] comme variable substitutive des concentrations en circulation et encourageons la realisation de travaux visant a expliquer l'incoherence observee. [Traduit par la Redaction] Mots-cles : Urocitellus parryii, spermophile arctique, hormones fecales, etat reproducteur, thyroide, thyroxine, triiodothyronine., Introduction Physiological and behavioral flexibility allows free-living vertebrates to cope with environmental heterogeneity, including predictable seasonal changes and unpredictable challenges. Adjustments of physiology and behavior to environmental conditions are often [...]

Stable isotope mixing models (SIMMs) are widely used for characterizing wild animal diets. Such models rely upon using accurate trophic discrimination factors (TDFs) to account for the digestion, incorporation, and assimilation of food. Existing methods to calculate TDFs rely on controlled feeding trials that are time‐consuming, often impractical for the study taxon, and may not reflect natural variability of TDFs present in wild populations.We present TDFCAM as an alternative approach to estimating TDFs in wild populations, by using high‐precision diet estimates from a secondary methodological source—in this case nest cameras—in lieu of controlled feeding trials, and provide a framework for how and when it should be applied.In this study, we evaluate the TDFCAM approach in three datasets gathered on wild raptor nestlings (gyrfalcons Falco rusticolus; peregrine falcons Falco perigrinus; common buzzards Buteo buteo) comprising contemporaneous δ13C & δ15N stable isotope data and high‐quality nest camera dietary data. We formulate Bayesian SIMMs (BSIMMs) incorporating TDFs from TDFCAM and analyze their agreement with nest camera data, comparing model performance with those based on other relevant TDFs. Additionally, we perform sensitivity analyses to characterize TDFCAM variability, and identify ecological and physiological factors contributing to that variability in wild populations.Across species and tissue types, BSIMMs incorporating a TDFCAM outperformed any other TDF tested, producing reliable population‐level estimates of diet composition. We demonstrate that applying this approach even with a relatively low sample size (n < 10 individuals) produced more accurate estimates of trophic discrimination than a controlled feeding study conducted on the same species. Between‐individual variability in TDFCAM estimates for ∆13C & ∆15 N increased with analytical imprecision in the source dietary data (nest cameras) but was also explained by natural variables in the study population (e.g., nestling nutritional/growth status and dietary composition).TDFCAM is an effective method of estimating trophic discrimination in wild animal populations. Here, we use nest cameras as source dietary data, but this approach is applicable to any high‐accuracy method of measuring diet, so long as diet can be monitored over an interval contemporaneous with a tissue's isotopic turnover rate. [ABSTRACT FROM AUTHOR]

Circadian systems are principally entrained to 24 h light--dark cycles, but this cue is seasonally absent in polar environments. Although some resident polar vertebrates have weak circadian clocks and are seasonally arrhythmic, the arctic ground squirrel (AGS) maintains daily rhythms of physiology and behavior throughout the summer, which includes 6 weeks of constant daylight. Here, we show that persistent daily rhythms in AGS are maintained through a circadian system that readily entrains to the polar day yet remains insensitive to entrainment by rapid light--dark transitions, which AGS generate naturally as a consequence of their semi-fossorial behavior. Additionally, AGS do not show 'jet lag', the slow realignment of circadian rhythms induced by the inertia of an intrinsically stable master circadian clock in the suprachiasmatic nucleus (SCN). We suggest this is due to the low expression of arginine vasopressin in the SCN of AGS, as vasopressin is associated with inter-neuronal coupling and robust rhythmicity. [ABSTRACT FROM AUTHOR]

Tactics of resource use for reproduction are an important feature of life-history strategies. A distinction is made between 'capital' breeders, which finance reproduction using stored energy, and 'income' breeders, which pay for reproduction using concurrent energy intake. In reality, vertebrates use a continuum of capital-to-income tactics, and, for many species, the allocation of capital towards reproduction is a plastic trait. Here, we review how trophic interactions and the timing of life-history events are influenced by tactics of resource use in birds and mammals. We first examine how plasticity in the allocation of capital towards reproduction is linked to phenological flexibility via interactions between endocrine/neuroendocrine control systems and the sensory circuits that detect changes in endogenous state, and environmental cues. We then describe the ecological drivers of reproductive timing in species that vary in the degree to which they finance reproduction using capital. Capital can be used either as a mechanism to facilitate temporal synchrony between energy supply and demand or as a means of lessening the need for synchrony. Within many species, an individual's ability to cope with environmental change may be more tightly linked to plasticity in resource allocation than to absolute position on the capital-to-income breeder continuum.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'., (© 2017 The Author(s).)

Stable carbon isotope ratios (δ 13 C) in breath show promise as an indicator of immediate metabolic fuel utilization in animals because tissue lipids have a lower δ 13 C value than carbohydrates and proteins. Metabolic fuel consumption is often estimated using the respiratory exchange ratio (RER), which has lipid and carbohydrate boundaries, but does not differentiate between protein and mixed fuel catabolism at intermediate values. Because lipids have relatively low δ 13 C values, measurements of stable carbon isotopes in breath may help distinguish between catabolism of protein and mixed fuel that includes lipid. We measured breath δ 13 C and RER concurrently in arctic ground squirrels (Urocitellus parryii) during steady-state torpor at ambient temperatures from -2 to -26°C. As predicted, we found a correlation between RER and breath δ 13 C values; however, the range of RER in this study did not reach intermediate levels to allow further resolution of metabolic substrate use with the addition of breath δ 13 C measurements. These data suggest that breath δ 13 C values are 1.1‰ lower than lipid tissue during pure lipid metabolism. From RER, we determined that arctic ground squirrels rely on nonlipid fuel sources for a significant portion of energy during torpor (up to 37%). The shift toward nonlipid fuel sources may be influenced by adiposity of the animals in addition to thermal challenge., (Copyright © 2017 Elsevier Inc. All rights reserved.)