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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) [...]

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 [...]

Reproductive costs must be balanced with survival to maximize lifetime reproductive rates; however, some organisms invest in a single, suicidal bout of breeding known as semelparity. The northern quoll (Dasyurus hallucatus) is an endangered marsupial in which males, but not females, are semelparous. Northern quolls living near mining sites on Groote Eylandt, Northern Territory, Australia, accumulate manganese (Mn) in their brains, testes, and hair, and elevated Mn impacts motor performance. Whether Mn is associated with other health declines is yet unknown. In the present study we show that male and female northern quolls with higher Mn accumulation had a 20% reduction in immune function and a trend toward reduced cortisol concentrations in hair. The telomere lengths of male quolls did not change pre‐ to postbreeding, but those with higher Mn levels had longer telomeres; in contrast, the telomeres of females shortened during the breeding season but recovered between the first year and second year of breeding. In addition, the telomeres of quolls that were recaptured declined at significantly higher rates in quolls with higher Mn between prebreeding, breeding, and/or postbreeding seasons. Future research should determine whether changes in cortisol, immune function, or telomere length affect reproductive output or survival—particularly for semelparous males. Environ Toxicol Chem 2024;43:74–86. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]