Survivable hypothermia or torpor in a wild-living rat: rare insights broaden our understanding of endothermic physiology

Convergent accelerated evolution of mammal-specific conserved non-coding elements in hibernators

Mammals maintain their body temperature, yet hibernators can temporarily lower their metabolic rate as an energy-saving strategy. It has been proposed that hibernators evolved independently from homeotherms, and it is possible that the convergent evolution of hibernation involved common genomic changes among hibernator-lineages. Since hibernation is a seasonal trait, the evolution of gene regulatory regions in response to changes in season may have been important for the acquisition of hibernation traits. High-frequency accumulation of mutations in conserved non-coding elements (CNEs) could, in principle, alter the expression of neighboring genes and thereby contribute to the acquisition of new traits. To address this possibility, we performed a comparative genomic analysis of mammals to identify accelerated CNEs commonly associated with hibernation. We found that accelerated CNEs are common to hibernator-lineages and could be involved with hibernation. We also found that common factors of genes that located near accelerated CNEs and are differentially expressed between normal and hibernation periods related to gene regulation and cell-fate determination. It suggests that the molecular mechanisms controlling hibernation have undergone convergent evolution. These results help broaden our understanding of the genetic adaptations that facilitated hibernation in mammals and may offer insights pertaining to stress responses and energy conservation.

Rare and Opportunistic Use of Torpor in Mammals-An Echo from the Past?

Torpor was traditionally seen as a winter survival mechanism employed by animals living in cold and highly seasonal habitats. Although we now know that torpor is also used by tropical and subtropical species, and in response to a variety of triggers, torpor is still largely viewed as a highly controlled, seasonal mechanism shown by Northern hemisphere species. To scrutinize this view, we report data from a macroanalysis in which we characterized the type and seasonality of torpor use from mammal species currently known to use torpor. Our findings suggest that predictable, seasonal torpor patterns reported for Northern temperate and polar species are highly derived forms of torpor expression, whereas the more opportunistic and variable forms of torpor that we see in tropical and subtropical species are likely closer to the patterns expressed by ancestral mammals. Our data emphasize that the torpor patterns observed in the tropics and subtropics should be considered the norm and not the exception.

Saving energy via short and shallow torpor bouts

Maintaining a high and stable body temperature as observed in most endothermic mammals and birds is energetically costly and many heterothermic species reduce their metabolic demands during energetic bottlenecks through the use of torpor. With the increasing number of heterotherms revealed in a diversity of habitats, it becomes apparent that triggers and patterns of torpor use are more variable than previously thought. Here, we report the previously overlooked use of, shallow rest-time torpor (body temperature >30 °C) in African lesser bushbabies, Galago moholi. Body core temperature of three adult male bushbabies recorded over five months showed a clear bimodal distribution with an average active modal temperature of 39.2 °C and a resting modal body temperature of 36.7 °C. Shallow torpor was observed in two out of three males (n = 29 torpor bouts) between June and August (austral winter), with body temperatures dropping to an overall minimum of 30.7 °C and calculated energy savings of up to 10%. We suggest that shallow torpor may be an ecologically important, yet mostly overlooked energy-saving strategy employed by heterothermic mammals. Our data emphasise that torpor threshold temperatures need to be used with care if we aim to fully understand the level of physiological plasticity displayed by heterothermic species.

Mechanistic considerations for adenosine-lidocaine-magnesium (ALM) in controlling coagulopathy

Adenosine-lidocaine-magnesium (ALM) mixture is a cardioplegic agent that improves survivability in rodent, but not swine, models of noncompressible torso hemorrhage (NCTH). However, despite protection from comorbid coagulopathy being the one common effect reported in both NCTH models, the underlying prothrombotic mechanism for ALM has not been elucidated in either. Here, we undertook a component-based approach focusing on individual drugs in the mixture to elaborate on the protective mechanism against coagulopathy within the frames of adenosine signaling and metabolic pathways. Additionally, the translational potential of small and large animal models of NCTH for human survival is critically appraised, owing to substantial quantitative/qualitative differences between humans and rodents, particularly regarding the genetics of G protein-coupled receptors (GPCRs) interacting with ALM's constituents.

Siberian hamsters nonresponding to short photoperiod use fasting-induced torpor

Nonresponding Siberian hamsters Phodopus sungorus do not develop the winter phenotype with white fur, low body mass (mb) and spontaneous torpor use in response to short photoperiod. However, their thermoregulatory response to fasting remains unknown. We measured body temperature and mb of 12 nonresponders acclimated to short photoperiod and then to cold, and fasted four times for 24h. Four individuals used torpor and in total we recorded 19 torpor bouts, which were shallow, short, and occurred at night. Moreover fasting increased the heterothermy index in all hamsters. Low mb was not a prerequisite for torpor use and mb loss correlated with neither heterothermy index nor torpor use. This is the first evidence that individuals which do not develop the winter phenotype, can use torpor or increase body temperature variability to face unpredictable, adverse environmental conditions. Despite the lack of seasonal changes, thermoregulatory adjustments may increase winter survival probability of nonresponders.