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A critical time in the life of a male occurs at reproduction, when his behaviour, physiology and resources must be brought to bear for the central purpose of his life—propagating his genes. We ask whether reproduction results in dysfunction of the stress axis, is linked to life history, and causes senescence. We assessed if deterioration in the axis underlies variation in reproductive lifespan in males of five species of North American ground squirrels whose life history varies from near semelparity to iteroparity. The most stressful and energy-demanding time occurs in spring during the intense 2–3 week breeding competition just after arousal from hibernation. We compared their stress axis functioning before and after the mating period using a hormonal challenge protocol. We found no evidence of stress axis dysfunction after reproduction in any species nor was there a relationship between reproductive lifespan and stress axis functional deterioration. Moreover, there was no consistent relationship between free cortisol levels and downstream measures (energy mobilization, haematology, immunity and body indices of condition). Thus, stress axis function was not traded off to promote reproduction irrespective of life history and lifespan, and we conclude that it is a prerequisite for life. Hence, it functions as a constraint and does not undergo senescence. [ABSTRACT FROM AUTHOR]

Telomeres are specialized non-coding DNA sequences located at the end of chromosomes and that protect genetic information. Telomere loss over lifespan is generally viewed as a phenomenon associated with aging in animals. Recently, telomere elongation after hibernation has been described in several mammals. Whether this pattern is an adaptation to repair DNA damage caused during rewarming from torpor or if it coevolved as a mechanism to promote somatic maintenance in preparation for the upcoming reproductive effort remains unclear. In a longitudinal study measuring telomere length using buccal swabs, we tested if telomere elongation was related to reproductive success in wild adult female Columbian ground squirrels (Urocitellus columbianus) that were monitored from emergence from hibernation to the end of the reproductive season. We found three key results. First, female telomere length increased at the start of the breeding season, both in breeding and non-breeding individuals. Second, post-emergence telomere lengthening was unrelated to female future reproductive output. Third, telomere length decreased in breeding females during lactation, but remained stable in non-breeding females over a similar period. Within breeders, telomeres shortened more in females producing larger and heavier litters. We concluded that telomere lengthening after hibernation did not constrain immediate female reproductive capacities. It was more likely to be part of the body recovery process that takes place after hibernation. Telomere erosion that occurs after birth may constitute a physiological cost of female reproduction. [ABSTRACT FROM AUTHOR]

Abstract: We examined hematological parameters in four related sciurid species in the late summer–autumn to assess the role of habitat, elevation, body size, and behavior in shaping these parameters. Red squirrels (Tamiasciurus hudsonicus) and Arctic ground squirrels (Spermophilus parryii) were sampled in southwestern Yukon, yellow-pine chipmunks (Tamias amoenus) in southern Alberta, and the eastern grey squirrel (Sciurus carolinensis) in southern Ontario. We obtained whole blood samples from each species and compared glucose levels, red blood cell characteristics (hematocrit, red blood cell count, hemoglobin concentration, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration), and white blood cell counts (neutrophils, lymphocytes, monocytes, eosinophils, basophils) across species. We found species differences in glucose and red blood cell characteristics that may be a function of activity levels, phylogeny, or elevation, but not of body size, body condition, or adaptations to a semi-fossorial habitat. We also found species differences in white blood cell counts that remain unexplained by any single simple explanation and may be more useful for comparison of individuals within a given species than for interspecies comparisons. [Copyright &y& Elsevier]

Northern environments present ecological and physiological problems for homeotherms that require adaptations to cope with severe and less predictable physical factors while at the same time continuing to have to cope with the biological ones, such as competition and predation. The stress axis plays a central role in these adaptations and I discuss the range of solutions that birds and mammals have evolved. The stress response in these animals is not static when a challenge occurs, but may be modulated depending on the biological function during the annual cycle (breeding versus nonbreeding), either under-responding to permit reproduction (some song birds) or responding vigorously, yet not having this compromise reproduction (Arctic ground squirrels). Both may trade off survival for reproduction. In contrast, the snowshoe hare shows the expected stress response to chronic high predation risk over 2-3 years: body resources are geared to survival and reproduction is inhibited. Two long term, persistent, and pervasive changes will confront northern birds and mammals in the 21st century: global change and persistent organochlorine pollutants (POPs). These may result in either adaptations or shifts in distribution and abundance. For the former, latitudinal variation in the stress axis may help song birds respond rapidly; population variation in the stress axis response is unknown in northern mammals and relatively sedentary mammals may be unable to shift their distribution rapidly to adjust major climate shifts. For the latter, the few POPs studies that have examined the stress axis indicate marked negative effects. [ABSTRACT FROM AUTHOR]

We examined how glucocorticoid and testosterone concentrations changed from spring to summer by livetrapping free-living populations of arctic ground squirrels (Spermophilus parryii). The primary glucocorticoid was found to be cortisol, with corticosterone below measurable concentrations in most individuals. Livetrapping elicited a strong stress response in both sexes: breeding males and females trapped in spring had free cortisol concentrations 4 and 34 times, respectively, those of base-line animals. The maximum corticosteroid-binding capacity (MCBC) was unaffected by trapping and was about 3 times higher in breeding females than in breeding males. Over the active season, MCBC values were lowest in all male classes (juveniles, nonreproductive adults, and reproductive adults), being less than half those in all female classes; pregnant females had values approximately twice those of juvenile females. However, free cortisol concentrations were similar in all female classes and in juvenile males and about half those in adult males. Livetrapping increased testosterone concentrations in males over those found in samples from base-line males, and testosterone concentrations did not affect MCBC values. Testosterone concentrations in livetrapped animals differed significantly among male classes, with nonreproductive males maintaining concentrations 64% of those in breeding males and 10 times those in juveniles.Nous avons examiné les variations des concentrations de glucocorticoïdes et de testostérone du printemps à l'été par piégeage d'animaux vivants dans des populations de Spermophiles arctiques (Spermophilus parryii) en nature. Le principal glucocorticoïde est le cortisol; la corticostérone est présente en quantité trop faible pour être décelée chez la plupart des individus. Le piégeage déclenche une forte réaction de stress chez les deux sexes; chez les individus reproducteurs, mâles et femelles, au printemps les animaux piégés avaient des concentrations de cortisol 4 et 34 fois plus élevées respectivement que les valeurs de base. La capacité maximale de liaison des corticostéroïdes (MCBC) n'a pas été affectée par le piégeage et était environ 3 fois plus élevée chez les femelles reproductrices que chez les mâles. Pendant la saison d'activité, les valeurs de MCBC étaient plus faibles chez les mâles de toutes les classes (juvéniles, adultes non reproducteurs et adultes reproducteurs), et équivalaient à la moitié de celles des femelles de toutes les classes d'âge et les femelles enceintes avaient des valeurs environ deux fois plus élevées que celles des femelles juvéniles. Cependant, les concentrations de cortisol libre étaient semblables chez toutes les classes de femelles et chez les mâles juvéniles et équivalaient à environ la moitié de celles des mâles adultes. Le piégeage a entraîné une augmentation des concentrations de testostérone chez les mâles par rapport aux concentrations de base et les concentrations de testostérone n'ont pas affecté les valeurs de MCBC. Les concentrations de testostérone chez les animaux capturés vivants différaient significativement d'une classe à l'autre chez les mâles et les mâles non reproducteurs avaient des concentrations équivalentes à 64 % de celles rencontrées chez les reproducteurs et à 10 fois celles des juvéniles.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Presents a report on the population of arctic ground squirrels and how such population statistics can be determined. Why there are limits to population increases; Processes that prevent population growth, including those that are density-dependent and density-independent; How the processes result in strong, density-dependent convergence of experimentally increased populations to those of control populations that had been at low, stable levels.

• We measured cortisol and oxidative stress responses to captures in Columbian ground squirrels. • Cortisol increased markedly slower than in other birds and mammals. • Cortisol responses were down-regulated in weaning females, but not post-reproductive males. • Oxidative stress increased slightly in response to captures in both sexes. • Species-specific validations are needed to design field protocols and interpret data. The measurement of glucocorticoid (GC) hormones provides us with a window into the stress physiology of vertebrates and the adaptative responses they use to cope with predictable and unpredictable changes in the environment. Baseline GCs inform us about the metabolic demands they are subject to at that point in their yearly life-history stage, whereas GC changes (often increases) in response to acute challenges inform us on their capacity to cope with more immediate environmental challenges. However, baseline GC levels and the kinetics of GC responses to acute stressors can vary substantially among and within species, depending on individual characteristics (age, sex, condition, life-history stage). In addition, a thorough understanding of the stress status of an animal requires moving beyond the measurement of GCs alone by focusing on downstream measures of metabolic activation, such as oxidative stress. Here, we evaluated the changes in blood cortisol and oxidative stress markers in wild adult Columbian ground squirrels (Urocitellus columbianus), following a 30-min capture-handling stress performed in mid-late June. Measurements were taken when males were post-reproductive and preparing for hibernation and adult females were weaning litters. We found three key results. First, the time-course of GC increase was markedly slower (by an order of magnitude) than what is currently reported in the literature for most species of mammals, birds and reptiles. Second, there were marked differences in the male and female response, linked to differences in life-history stage: females close to weaning had abolished GC responses, whereas post-reproductive males did not. Third, there were mild to moderate increases in oxidative damage and decreases in oxidative defenses in response to our short-term challenge, consistent with the idea that short-term acute metabolic activation may carry physiological costs. However, these changes were not correlated to the changes in GCs, a novel result suggesting a disconnect between the hormonal stress response and oxidative damage. [ABSTRACT FROM AUTHOR]

Inclement weather can rapidly modify the thermal conditions experienced by animals, inducing changes in their behavior, body condition, and stress physiology, and affecting their survival and breeding success. For animals living in variable environments, the extent to which they have adapted to cope with inclement weather is not established, especially for hibernating species with a short active season that are constrained temporally to breed and store energy for subsequent hibernation. We examined behavioral (foraging activity) and physiological (body mass and fecal cortisol metabolites) responses of Columbian ground squirrels (Urocitellus columbianus), small hibernating rodents inhabiting open meadows in Rocky Mountains, to 3 events of inclement weather (two snow storms in May 2021 and May 2022, one heavy rainfall in June 2022). We found that individuals adapted to inclement weather conditions by (1) reducing above-ground activity, including foraging, (2) decreasing the mobilization of stored resources as indicated by a decrease in the activity of the hypothalamo-pituitary-adrenal (HPA) axis and lower fecal cortisol metabolites in the hours/days following periods of inclement weather; and (3) compensating through increased foraging and more local activity when favorable conditions resumed. As a result, body mass and growth did not decrease following short periods of inclement weather. Columbian ground squirrels were well-adapted to short periods of inclement weather, coping via modifications of their behavior and the activity of the HPA axis. [Display omitted] • Columbian ground squirrels are montane rodents that occupy habitats in rapidly changing environments. • Activity, foraging, and space utilization decreased during inclement weather during the breeding season. • Fecal cortisol metabolite levels were lower after inclement weather than during control periods. • Body mass and body mass gain were not affected by days of inclement weather. • These ground squirrels appeared well adapted to inclement weather. [ABSTRACT FROM AUTHOR]

Social environments can profoundly affect the behavior and stress physiology of group-living animals. In many territorial species, territory owners advertise territorial boundaries to conspecifics by scent marking. Several studies have investigated the information that scent marks convey about donors' characteristics (e.g., dominance, age, sex, reproductive status), but less is known about whether scents affect the behavior and stress of recipients. We experimentally tested the hypothesis that scent marking may be a potent source of social stress in territorial species. We tested this hypothesis for Columbian ground squirrels (Urocitellus columbianus) during lactation, when territorial females defend individual nest-burrows against conspecifics. We exposed lactating females, on their territory, to the scent of other lactating females. Scents were either from unfamiliar females, kin relatives (a mother, daughter, or sister), or their own scent (control condition). We expected females to react strongly to novel scents from other females on their territory, displaying increased vigilance, and higher cortisol levels, indicative of behavioral and physiological stress. We further expected females to be more sensitive to unfamiliar female scents than to kin scents, given the matrilineal social structure of this species and known fitness benefits of co-breeding in female kin groups. Females were highly sensitive to intruder (both unfamiliar and kin) scents, but not to their own scent. Surprisingly, females reacted more strongly to the scent of close kin than to the scent of unfamiliar females. Vigilance behavior increased sharply in the presence of scents; this increase was more marked for kin than unfamiliar female scents, and was mirrored by a marked 131% increase in free plasma cortisol levels in the presence of kin (but not unfamiliar female) scents. Among kin scents, lactating females were more vigilant to the scent of sisters of equal age, but showed a marked 318% increase in plasma free cortisol levels in response to the scent of older and more dominant mothers. These results suggest that scent marks convey detailed information on the identity of intruders, directly affecting the stress axis of territory holders. • Scent-marking is an important means of social communication in territorial species. • Scents introduced on territories of female ground squirrels increase vigilance. • Females react more strongly to the scent of female kin than unfamiliar females. • Kin scents cause a marked increase in plasma cortisol levels. • Scents of mothers cause higher cortisol elevations than sister or daughter scents. [ABSTRACT FROM AUTHOR]