Absence of heterothermy in the European red squirrel (Sciurus vulgaris)

Dausmann, Kathrin H.; Wein, Jens; Turner, James M.; Glos, Julian

doi:10.1016/j.mambio.2013.01.004

Cited by 15 publications

(9 citation statements)

References 25 publications

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“…However, a decrease in T b during winter can not only be observed in heterothermic species, but also, to a lesser degree, in homeothermic species. The homeothermic, European red squirrels (Sciurus vulgaris), for example, lower their T b slightly during the winter [99]. This has also been observed in large mammals, such as the red deer (Cervus elaphus) [27] or the Przewalski horse (Equus ferus przewalskii) [100].…”

Section: Seasonality and Unpredictability Of Mammalian T Bmentioning

confidence: 77%

Modelling mammalian energetics: the heterothermy problem

Levesque

Nowack

Stawski

2016

Clim Chang Responses

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Global climate change is expected to have strong effects on the world's flora and fauna. As a result, there has been a recent increase in the number of meta-analyses and mechanistic models that attempt to predict potential responses of mammals to changing climates. Many models that seek to explain the effects of environmental temperatures on mammalian energetics and survival assume a constant body temperature. However, despite generally being regarded as strict homeotherms, mammals demonstrate a large degree of daily variability in body temperature, as well as the ability to reduce metabolic costs either by entering torpor, or by increasing body temperatures at high ambient temperatures. Often, changes in body temperature variability are unpredictable, and happen in response to immediate changes in resource abundance or temperature. In this review we provide an overview of variability and unpredictability found in body temperatures of extant mammals, identify potential blind spots in the current literature, and discuss options for incorporating variability into predictive mechanistic models.

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Section: Seasonality and Unpredictability Of Mammalian T Bmentioning

confidence: 77%

Modelling mammalian energetics: the heterothermy problem

Levesque

Nowack

Stawski

2016

Clim Chang Responses

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“…This strategy, however, could be conceivable for members of the Sciuridae, which includes the classic hibernators (ground squirrels and chipmunks in the clade Marmotini). Interestingly, tree squirrels (sub-family Sciurinae) including European red squirrels (Sciurus vulgaris), have not been observed to enter torpid states (Dausmann et al, 2013), although it appears likely that closely-related flying squirrels are capable of shallow torpor (Olson et al, 2017). Tropical and sub-tropical sciurids have not been studied and more field studies are clearly needed to elucidate the potential for rare use of torpor in otherwise homeothermic mammals.…”

Section: Rare Use Of Torpormentioning

confidence: 99%

Variable Climates Lead to Varying Phenotypes: “Weird” Mammalian Torpor and Lessons From Non-Holarctic Species

Nowack

Levesque

Reher³

et al. 2020

Front. Ecol. Evol.

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Mammalian heterotherms, species that employ short or long periods of torpor, are found in many different climatic regions. Although the underlying physiological mechanisms of heterothermy in species from lower latitudes (i.e., the tropics and southern hemisphere) appear analogous to those of temperate and arctic heterotherms, the ultimate triggers and resulting patterns of energy expenditure and body temperature are often noticeably different. Phenotypic flexibility in the patterns of thermoregulation in non-Holarctic species can be extensive (depending on body condition, environmental parameters and species competition) and the factors responsible for inducing heterothermy are more variable in non-Holarctic species. As well as being a regular adaptation to seasonality, heterothermy can also be employed as a response to unpredictability in environmental parameters and as a response to emergency situations. Non-Holarctic heterotherms also challenge the notion that regular inter-bout arousals during hibernation are obligatory and suggest all that is necessary to maintain proper functioning during hibernation is an occasional passive return to-or maintenance of-a relatively high body temperature. The study of non-Holarctic heterotherms has led to the conclusion that heterothermy must be defined on the basis of mechanistic, physiological parameters, and not solely by body temperature; yet we are still limited in our abilities to record such mechanistic parameters in the field. It is now believed that homeothermy in mammals evolved in hot climates via an ancestral heterothermic state. Similar to extant warm-climate heterotherms, early mammals could have relied mainly on passive body temperature regulation with a capacity for short-to longer-term up-regulation of metabolism when needed. Hibernation, as seen in temperate and arctic species may then be a derived state of this ancestral heterothermy, and the study of torpor in warm climates can provide potential models for the energetics of early mammals.

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“…Among all these groups, hibernation has been most extensively studied within the squirrel family, Sciuridae, which includes hibernating ground squirrels, chipmunks, marmots and prairie dogs. The expression of torpor is highly variable among sciurid species, with some exhibiting only daily episodes, others exhibiting multiday torpor bouts as long as 24 days repeated over the course of a hibernation season (Geiser & Ruf, 1995) and others that do not express torpor at all (Kenagy, 1981a;Brigham & Geiser, 2012;Dausmann et al, 2013). This review focuses on sciurids that hibernate, including 'obligate' hibernators, which predictably exhibit hibernation each year, and 'facultative' hibernators, which manifest the trait only under certain environmental conditions (Kenagy, 1981b;Humphries, Kramer & Thomas, 2003;Lehmer et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Phenology of hibernation and reproduction in ground squirrels: integration of environmental cues with endogenous programming

et al. 2013

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Mammalian hibernation is characterized by prolonged dormancy consisting of pronounced depression of metabolism and body temperature. Though hibernation occurs in at least seven mammalian orders and several families of the order Rodentia, the ecology and physiology of hibernation in rodents has been most extensively studied in the family Sciuridae, particularly in the so‐called ground squirrels, that is, the tribe Marmotini. Early studies of these rodents demonstrated the important role of an endogenous circannual clock in the persistence of annual timing and phasing of key seasonal events, including weight gain, hibernation and reproduction. Here, we review the causes and consequences of intraspecific variation in the timing of hibernation and reproduction in these sciurids and examine the physiological mechanisms that contribute to phenotypic plasticity in seasonal timing. Although the duration, annual phasing and predictability of seasonal change in environmental conditions likely promoted the evolution of endogeneity, precision and brevity of breeding seasons in the annual cycles of sciurids, substantial intraspecific variation in hibernation and reproductive phenology exists along latitudinal and altitudinal clines, as well as among locally varying environmental micro‐conditions. We suggest that much of this variation is a function of plasticity in the physiological mechanisms controlling annual cycles. While studies of captive animals have been instrumental in establishing the role of an endogenous rhythm, a greater emphasis on experimental field manipulations is needed to better understand the function, causes and consequences of phenological shifts in wild populations. Ultimately, the capacity of hibernators to adjust their timing in response to changing environmental conditions, either through phenotypic plasticity or microevolution, will be an important determinant of the resilience of sciurid species to changing climate.

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Absence of heterothermy in the European red squirrel (Sciurus vulgaris)

Cited by 15 publications

References 25 publications

Modelling mammalian energetics: the heterothermy problem

Modelling mammalian energetics: the heterothermy problem

Variable Climates Lead to Varying Phenotypes: “Weird” Mammalian Torpor and Lessons From Non-Holarctic Species

Phenology of hibernation and reproduction in ground squirrels: integration of environmental cues with endogenous programming

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