Thermal Tolerance and Preferred Temperature in the Critical Endangered Montseny Brook Newt (Calotriton arnoldi)

Climate change, driven by increased human greenhouse gas emissions since the beginning of the industrial revolution up to the present day, is considered one of the major threats to biodiversity in the twenty-first century. One of the most affected groups is the ectotherms due to their direct dependence on environmental temperatures. In recent years, several studies have analysed the effects of temperature and thermal tolerance on several species of ectotherms. However, there are species whose thermal tolerances are still unknown. Such is the case of the critically endangered species, the Montseny Brook Newt (Calotriton arnoldi), endemic to the Montseny massif in Spain and whose thermal biology is unknown. Its critical situation makes it essential to know its tolerance to cooling, warming and thermopreferendum in water environments where the newt lives. Three experimental procedures were conducted from the western and eastern subspecies of C. arnoldi, considering four classes separately (males, females, juveniles and larvae). The results obtained showed that the CTmax of the species exceeded 31 °C, with a significant difference between the two subspecies. We found that the species tolerates low temperatures (<1 °C) well because the genera Calotriton is adapted to live in cold waters with temperatures below 15 °C. Although the thermopreference of the species was expected to trend to cold temperatures, some individuals chose relatively high temperatures, obtaining a range of 11.7 °C to 21.6 °C. The results presented in this study are an advance in the knowledge of the thermal physiology of this species and support the importance of the temperature of the torrent on its survival. Knowing their thermal limits and their preferred temperature range will help to propose management measures that promote the conservation of streams and riparian forest cover to mitigate temperature increases due to climate change.

Longer days, larger grays: carryover effects of photoperiod and temperature in gray treefrogs, Hyla versicolor

Environmental conditions like temperature and photoperiod can strongly shape organisms' growth and development. For many ectotherms with complex life cycles, global change will cause their offspring to experience warmer conditions and earlier-season photoperiods, two variables that can induce conflicting responses. We experimentally manipulated photoperiod and temperature during gray treefrog (Hyla versicolor) larval development to examine effects at metamorphosis and during short (10-day) and long (56-day) periods post-metamorphosis. Both early- and late-season photoperiods (April and August) decreased age and size at metamorphosis relative to the average-season (June) photoperiod, while warmer temperatures decreased age but increased size at metamorphosis. Warmer larval temperatures reduced short-term juvenile growth but had no long-term effect. Conversely, photoperiod had no short-term carryover effect, but juveniles from early- and late-season larval photoperiods had lower long-term growth rates than juveniles from the average-season photoperiod. Similar responses to early- and late-season photoperiods may be due to reduced total daylight compared with average-season photoperiods. However, juveniles from late-season photoperiods selected cooler temperatures than early-season juveniles, suggesting that not all effects of photoperiod were due to total light exposure. Our results indicate that despite both temperature and photoperiod affecting metamorphosis, the long-term effects of photoperiod may be much stronger than those of temperature.

Gluconeogenesis in frogs during cooling and dehydration exposure: new insights into tissue plasticity of the gluconeogenic pathway dependent on abiotic factors

Anurans undergo significant physiological changes when exposed to environmental stressors such as low temperatures and humidity. Energy metabolism and substrate management play a crucial role in their survival success. Therefore, understanding the role of the gluconeogenic pathway and demonstrating its existence in amphibians is essential. In this study, we exposed the subtropical frog Boana pulchella to cooling (-2.5°C for 24 h) and dehydration conditions (40% of body water loss), followed by recovery (24 h), and assessed gluconeogenesis activity from alanine, lactate, glycerol and glutamine in the liver, muscle and kidney. We report for the first time that gluconeogenesis activity by 14C-alanine and 14C-lactate conversion to glucose occurs in the muscle tissue of frogs, and this tissue activity is influenced by environmental conditions. Against the control group, liver gluconeogenesis from 14C-lactate and 14C-glycerol was lower during cooling and recovery (P<0.01), and gluconeogenesis from 14C-glutamine in the kidneys was also lower during cooling (P<0.05). In dehydration exposure, gluconeogenesis from 14C-lactate in the liver was lower during recovery, and that from 14C-alanine in the muscle was lower during dehydration (P<0.05). Moreover, we observed that gluconeogenesis activity and substrate preference respond differently to cold and dehydration. These findings highlight tissue-specific plasticity dependent on the nature of the encountered stressor, offering valuable insights for future studies exploring this plasticity, elucidating the importance of the gluconeogenic pathway and characterizing it in anuran physiology.

Dynamics of epigenetic regulation in Dryophytes versicolor skeletal muscle: Lysine methylation and acetylation involvement in metabolic rate depression

For the breadth of the winter, Dryophytes versicolor can survive full body freezing utilizing a phenomenon known as metabolic rate depression (MRD). Epigenetic transcriptional control on gene expression, such as histone methylation and acetylation, can aid in implementing a balance between permissive and restricted chromatin required to endure this stress. As such, this study explores the interplay between histone lysine methyl and acetyl transferases (HKMTs, HATs), as well as the abundance of various acetyl-lysine and methyl-lysine moieties on histone H3 and H4. Results showing that overexpression of transcriptionally repressive marks, and under expression of active ones, suggest a negative effect on overall gene transcription in skeletal muscle tissue.

Comparative transcriptomic analysis delineates adaptation strategies of Rana kukunoris toward cold stress on the Qinghai-Tibet Plateau

BACKGROUND

Cold hardiness is fundamental for amphibians to survive during the extremely cold winter on the Qinghai-Tibet plateau. Exploring the gene regulation mechanism of freezing-tolerant Rana kukunoris could help us to understand how the frogs survive in winter.

RESULTS

Transcriptome of liver and muscle of R. kukunoris collected in hibernation and spring were assisted by single molecule real-time (SMRT) sequencing technology. A total of 10,062 unigenes of R. kukunoris were obtained, and 9,924 coding sequences (CDS) were successfully annotated. Our examination of the mRNA response to whole body freezing and recover in the frogs revealed key genes concerning underlying antifreeze proteins and cryoprotectants (glucose and urea). Functional pathway analyses revealed differential regulated pathways of ribosome, energy supply, and protein metabolism which displayed a freeze-induced response and damage recover. Genes related to energy supply in the muscle of winter frogs were up-regulated compared with the muscle of spring frogs. The liver of hibernating frogs maintained modest levels of protein synthesis in the winter. In contrast, the liver underwent intensive high levels of protein synthesis and lipid catabolism to produce substantial quantity of fresh proteins and energy in spring. Differences between hibernation and spring were smaller than that between tissues, yet the physiological traits of hibernation were nevertheless passed down to active state in spring.

CONCLUSIONS

Based on our comparative transcriptomic analyses, we revealed the likely adaptive mechanisms of R. kukunoris. Ultimately, our study expands genetic resources for the freezing-tolerant frogs.

Urea and glucose modulation during freezing exposure in three temperate frogs reveals specific targets in relation to climate

Amphibian diversity is most prominent in the warm and humid tropical and subtropical regions across the globe. Nonetheless, amphibians also inhabit high-altitude tropical mountains and regions at medium and high latitudes, exposing them to subzero temperatures and requiring behavioural or physiological adaptations to endure freezing events. While freeze tolerance has been predominantly reported in high-latitude zones where species endure prolonged freezing (several weeks or months), less is known about mid-latitudes amphibians exposed to occasional subzero temperatures. In this study, we employed a controlled ecological protocol, subjecting three frog species from the Iberian Peninsula (Rana parvipalmata, Epidalea calamita, and Pelobates cultripes) to a 2-h exposure to temperatures of -2 °C to investigate the accumulation of urea and glucose as physiological mechanisms associated with survival at freezing temperatures. Our results revealed a moderate response in the production of cryoprotectant metabolites under experimental freezing conditions, particularly urea, with notable findings in R. parvipalmata and E. calamita and no response in P. cultripes. However, no significant alterations in glucose concentrations were observed in any of the studied frog species. This relatively weak freezing tolerance response differs from the strong response exhibited by amphibians inhabiting high latitudes and enduring prolonged freezing conditions, suggesting potential reliance on behavioural adaptations to cope with occasional freezing episodes.

Transcriptome, histological, and physiological responses of Amur sleeper (Perccottus glenii) during cold stress, freezing, and recovery

Freeze tolerance is a survival strategy employed by some ectotherms living in extremely cold environments. Some fish in extremely cold areas can recover from their frozen state, but they also have to endure cold stress. Amur sleeper (Perccottus glenii) can recover from a completely frozen state. To explore the response of freeze-resistant fish to low temperatures, we analyzed histological alterations, and antioxidant and carbohydrate-lipid metabolizing enzymes of P. glenii under low temperatures. So far, sensory genes regulating P. glenii during cold stress, freezing, and recovery have not been identified. Ultrastructure results indicated that glycogen content and mitochondrial ridge decreased during cold stress and freezing, whereas the number of endoplasmic reticulum increased during recovery. Plasma glucose and glycerol levels of the three treatment groups significantly increased. Lactate dehydrogenase and pyruvate kinase levels significantly increased during cold stress and freezing, and hexokinase levels significantly increased during cold stress. In total, 30,560 unigenes were found (average length 1724 bp, N50 2843 bp). In addition, 7370 differentially expressed genes (DEGs; including 2938 upregulated genes and 4432 downregulated genes) were identified. KEGG analysis revealed that the DEGs were enriched in carbohydrate and lipid metabolism, lipid synthesis, immune system, and anti-apoptosis. Genes involved in glycolysis and phospholipid metabolism were significantly upregulated during cold stress; genes related to circadian rhythm, oxidative phosphorylation, and lipid synthesis were significantly upregulated during freezing; and genes involved in the immune system and anti-apoptosis were significantly upregulated during recovery. Our results attempt to offer new insights into the physiological mechanisms of complex adaptation in P. glenii and provide useful information for future studies on the mechanism underlying freezing/recovery in animals.

Novel observations of "freeze resistance" and dynamic blue and green dorsal coloration in frozen and thawing Dryophytes chrysoscelis

Freeze tolerant animals survive the winter by tolerating the freezing and thawing of up to 70% of body water and the respective cessation and resumption of essential functions including circulation and respiration during each freeze-thaw cycle. Cope's gray treefrog Dryophytes chrysoscelis is a freeze tolerant anuran that uses a system of cryoprotectants to prevent intracellular freezing and mitigate osmotic stress during freezing and thawing episodes. Morphological features were documented in D. chrysoscelis using a repeated freeze-thaw protocol. Dorsal skin in frozen frogs was distinctly blue and green before reverting to brown during thawing. The dorsal color change in frozen frogs does not function similarly to other known color change events in amphibians. The return to brown skin color in thawing animals coincides with recovery of vital functions in freeze tolerant frogs, suggesting that dorsal color change is an indicator of postfreeze recovery in D. chrysoscelis. We also provide evidence of "freeze resistance" in D. chrysoscelis. Two individuals did not freeze following three successive bouts of ice inoculation at -2.5°C and maintained brown dorsal color despite ice crystallization on the dorsum and contact with frozen substrate. Both frogs had similar plasma osmolality, circulating cryoprotectants, and incidence of cryoinjury compared to frogs that were frozen and thawed once or three times. Freeze resistance may be explained by physical changes in the skin including lipid accumulation and dehydration. This integrative study presents novel attributes of organismal freeze tolerance in D. chrysoscelis.

Hepatic transcriptome and gut microbiome provide insights into freeze tolerance in the high-altitude frog, Nanorana parkeri

Among amphibians, freeze tolerance is a low-temperature survival strategy that has been well studied in several species. One influence on animal health and survival under adverse conditions is the gut microbiome. Gut microbes can be greatly affected by temperature fluctuations but, to date, this has not been addressed in high-altitude species. Nanorana parkeri (Anura: Dicroglossidae) lives at high altitudes on the Tibetan plateau and shows a good freeze tolerance. In the present study, we addressed two goals: (1) analysis of the effects of whole body freezing on the liver transcriptome, and (2) assess modifications of the gut microbiome as a consequence of freezing. We found that up-regulated genes in liver were significantly enriched in lipid and fatty acid metabolism that could contribute to accumulating the cryoprotectant glycerol and raising levels of unsaturated fatty acids. The results suggest the crucial importance of membrane adaptations and fuel reserves for freezing survival of these frogs. Down-regulated genes were significantly enriched in the immune response and inflammatory response, suggesting that energy-consuming processes are inhibited to maintain metabolic depression during freezing. Moreover, freezing had a significant effect on intestinal microbiota. The abundance of bacteria in the family Lachnospiraceae was significantly increased after freezing exposure, which likely supports freezing survival of N. parkeri. The lower abundance of bacteria in the family Peptostreptococcaceae in frozen frogs may be associated with the hypometabolic state and decreased immune response. In summary, these findings provide insights into the regulatory mechanisms of freeze tolerance in a high-altitude amphibian at the level of gene expression and gut microbiome, and contribute to enhancing our understanding of the adaptations that support frog survival in high-altitude extreme environments.

Living in the mountains: Thermal ecology and freezing tolerance of the lizard Abronia taeniata (Squamata: Anguidae)

The impact of daily and seasonal variation in environmental temperature on lizards is important, since their physiological processes are body temperature dependent. Lizards that occupy mountainous areas must have been favoured to colonize such habitats through selection on thermal biology traits to thermoregulate effectively. Moreover, mountain lizards may be able to maintain their activity near their minimum critical temperature and even have antifreeze mechanisms. Tolerance of freezing is related to the biosynthesis of cryoprotective molecules, such as glucose, whose concentration may increase after freezing. The aims of the present work were: (1) study the thermoregulation of the viviparous lizard Abronia taeniata, and (2) determine its survival and/or tolerance to freezing. This species occurs in pine forests, pine-oak forests, and mountain mesophilic forests in areas that reach freezing temperatures. In the field, we recorded air, substrate, and body temperatures at capture time of the lizards, and registered operative temperatures at the study area. In the laboratory, we determined thermal preferences, crystallization point, and blood glucose levels of individuals before and after freezing. We found out that A. taeniata sustains activity in a wide range of temperatures, actively avoids thermally favourable microhabitats in spring, and is a moderate thermoregulator during autumn and winter. In A. taeniata, the body temperatures are tightly linked to air and substrate temperatures. Seasonality had an effect over body temperature, preferred temperatures and thermoregulatory effectiveness indices. When exposed to temperatures below zero, A. taeniata showed an increase in blood glucose levels, which aided them in surviving freezing. Taken together, our results suggest that A. taeniata may sustain activity at low environmental temperatures, due to an effective behavioural thermoregulation, and in case temperatures of its habitat go below zero, is also capable of tolerate freezing.

Commonly collected thermal performance data can inform species distributions in a data-limited invader

Predicting potential distributions of species in new areas is challenging. Physiological data can improve interpretation of predicted distributions and can be used in directed distribution models. Nonnative species provide useful case studies. Panther chameleons (Furcifer pardalis) are native to Madagascar and have established populations in Florida, USA, but standard correlative distribution modeling predicts no suitable habitat for F. pardalis there. We evaluated commonly collected thermal traits- thermal performance, tolerance, and preference-of F. pardalis and the acclimatization potential of these traits during exposure to naturally-occurring environmental conditions in North Central Florida. Though we observed temperature-dependent thermal performance, chameleons maintained similar thermal limits, performance, and preferences across seasons, despite long-term exposure to cool temperatures. Using the physiological data collected, we developed distribution models that varied in restriction: time-dependent exposure near and below critical thermal minima, predicted activity windows, and predicted performance thresholds. Our application of commonly collected physiological data improved interpretations on potential distributions of F. pardalis, compared with correlative distribution modeling approaches that predicted no suitable area in Florida. These straightforward approaches can be applied to other species with existing physiological data or after brief experiments on a limited number of individuals, as demonstrated here.

Osmotic and metabolic responses to cold acclimation and acute cold challenge in a freeze avoidant lizard, Podarcis siculus

Ectotherms survive exposure to subzero temperatures through freeze tolerance or freeze avoidance. Among vertebrate ectotherms, glucose is commonly used as a cryoprotectant in freeze tolerant strategies and as an osmolyte in freeze avoidant strategies, while also functioning as a metabolic substrate. Whereas some lizard species are capable of both freeze tolerance and freeze avoidance, Podarcis siculus is limited to freeze avoidance through supercooling. We hypothesized that, even in a freeze-avoidant species such as P. siculus, plasma glucose would accumulate with cold acclimation and would increase in response to acute exposure to subzero temperatures. To investigate this, we tested whether plasma glucose concentration and osmolality would increase in response to a subzero cold challenge before and after cold acclimation. In addition, we examined the relationship between metabolic rate, cold acclimation, and glucose by measuring metabolic rate during the cold challenge trials. We found that plasma glucose increased during the cold challenge trials, and that the increase was more pronounced after cold acclimation. However, baseline plasma glucose decreased throughout cold acclimation. Interestingly, total plasma osmolality did not change, and the increase in glucose only slightly altered freezing point depression. Metabolic rate during the cold challenge decreased after cold acclimation, and changes in respiratory exchange ratio suggest an increased relative use of carbohydrates. Overall, our findings demonstrate an important role for glucose in the response of P. siculus to an acute cold challenge, thus adding evidence for glucose as an important molecule for overwintering ectotherms that use freeze avoidant strategies.

Histone H3 and H4 Modifications Point to Transcriptional Suppression as a Component of Winter Freeze Tolerance in the Gall Fly Eurosta solidaginis

The goldenrod gall fly (Eurosta solidaginis) is a well-studied model of insect freeze tolerance. In situations of prolonged winter subzero temperatures, larvae of E. solidaginis accept ice penetration throughout extracellular spaces while protecting the intracellular environment by producing extreme amounts of glycerol and sorbitol as cryoprotectants. Hypometabolism (diapause) is implemented, and energy use is reprioritized to essential pathways. Gene transcription is one energy-expensive process likely suppressed over the winter, in part, due to epigenetic controls. The present study profiled the prevalence of 24 histone H3/H4 modifications of E. solidaginis larvae after 3-week acclimations to decreasing environmental temperatures (5 °C, -5 °C and -15 °C). Using immunoblotting, the data show freeze-mediated reductions (p < 0.05) in seven permissive histone modifications (H3K27me1, H4K20me1, H3K9ac, H3K14ac, H3K27ac, H4K8ac, H3R26me2a). Along with the maintenance of various repressive marks, the data are indicative of a suppressed transcriptional state at subzero temperatures. Elevated nuclear levels of histone H4, but not histone H3, were also observed in response to both cold and freeze acclimation. Together, the present study provides evidence for epigenetic-mediated transcriptional suppression in support of the winter diapause state and freeze tolerance of E. solidaginis.

Integrated analysis of transcriptome and metabolome data reveals insights for molecular mechanisms in overwintering Tibetan frogs, Nanorana parkeri

Nanorana parkeri (Anura, Dicroglossidae) is a unique frog living at high altitude on the Tibetan plateau where they must endure a long winter dormancy at low temperatures without feeding. Here, we presented a comprehensive transcriptomic and metabolomic analysis of liver tissue from summer-active versus overwintering N. parkeri, providing the first broad analysis of altered energy metabolism and gene expression in this frog species. We discovered that significantly up-regulated genes (2,397) in overwintering frogs mainly participated in signal transduction and immune responses, phagosome, endocytosis, lysosome, and autophagy, whereas 2,169 down-regulated genes were mainly involved in metabolic processes, such as oxidation-reduction process, amino acid metabolic process, fatty acid metabolic process, and TCA cycle. Moreover, 35 metabolites were shown to be differentially expressed, including 22 down-regulated and 13 up-regulated in winter. These included particularly notable reductions in the concentrations of most amino acids. These differentially expressed metabolites were mainly involved in amino acid biosynthesis and metabolism. To sum up, these findings suggest that gene expression and metabolic processes show adaptive regulation in overwintering N. parkeri, that contributes to maintaining homeostasis and enhancing protection in the hypometabolic state. This study has greatly expanded our understanding of the winter survival mechanisms in amphibians.

Hayvanlarda Soğuğa Dayanıklılık: Çift Yaşarların Kriyobiyolojisi

Organizmalar yaşamlarını devam ettirebilmek için abiyotik çevresel koşullara uyum sağlarlar. Özellikle ortam sıcaklığındaki değişimler; canlıların beslenme, üreme, gelişim ve morfolojileri üzerinde etkilidir. Sıra dışı sıcaklık değişimleri özellikle ektotermik hayvanlar için ölümcül olabilir. Karasal ektotermler. doğada donma noktasının altındaki sıcaklıklarda hayatta kalabilmek için davranışsal, fizyolojik ve biyokimyasal bazı özel stratejiler geliştirmişlerdir. Bazı türler göç ederek su ya da toprak altında kış uykusuna yatmak suretiyle dondurucu sıcaklıklardan kaçınırlar. Bazıları ise donma koşullarına maruz kalarak kışı geçirmek zorundadırlar. Genel olarak dondurucu soğuğa dayanıklılık donmadan kaçınma (süper soğuma) ve donma toleransı stratejilerine bağlıdır. Donmadan kaçınma durumunda vücut sıvılarının donma noktasının altındaki sıcaklıklarda sıvı formu korunurken donma toleransı stratejisini kullanan canlılarda ise vücutlarındaki toplam suyun %50’sinden fazlasının donması tolere edilebilir. Karasal hibernatör hayvanlardan bazı amfibi ve sürüngen gruplarında da tespit edilen donma toleransı stratejisi onların dondurucu kış koşullarında hayatta kalmalarını sağlamaktadır. Bu özel türler kriyoprotektif mekanizmaları ile donmanın ölümcül etkilerinden korunurlar. Donma süresince yaşamsal faaliyetleri tamamen duran bu hayvanlar çözündükten sonra kısa bir süre içerisinde de normal yaşama dönerler. Bu mucizevi mekanizmanın araştırılması yalnızca hayvanların karmaşık adaptasyonunu açıklamakla kalmaz, aynı zamanda doku ve hücre kriyoprezervasyon teknolojisine de kaynak sağlar. Bu derleme amfibilerin donma toleransı stratejilerine dair bilgiler sunarak henüz yeterince çalışılmamış bu konuda araştırma yapmak isteyenlere katkı sağlayacaktır.

Involvement of glucose in freeze tolerance in the Japanese tree frog Hyla japonica

Glycerol and aquaporin 9 (aquaglyceroporin) are known to be involved in freeze tolerance in the Japanese tree frog Hyla japonica. However, the regulatory mechanisms of freeze tolerance in this species have not been fully elucidated. In the present study, we focused on the inter- and intracellular dynamics of glucose to analyze the role of glucose and glucose-related proteins such as transporter and metabolic enzymes in freeze tolerance. Serum glucose concentrations were compared among the frogs that were nonhibernating, hibernating, and thawed after freezing at -4°C for 6 hr. Serum concentrations of glucose in thawed frogs were significantly higher than those in hibernating and nonhibernating, active frogs. Periodic acid-Schiff staining showed that the accumulation of glycogen in the hepatocytes increased before hibernation and decreased after freezing and thawing. Quantitative RT-PCR analysis using the liver showed that, compared with active frogs, the type 2 glucose transporter gene (glut2) was upregulated in frozen frogs, the liver glycogen phosphorylase gene (pygl) was upregulated in frozen or thawed frogs, and the type 2 glycogen synthase gene (gys2) was upregulated in hibernating frogs. Immunohistochemistry of liver sections showed that, compared with nonhibernating frogs, Glut2 proteins were clearly increased most likely on the plasma membrane of hepatocytes in hibernating frogs and further increased by freezing, then decreased after thawing. These results suggest the possibility that glucose acts as a cryoprotectant in H. japonica.

Physiological and biochemical differences in diapause and non-diapause pupae of Sericinus montelus (Lepidoptera: Papilionidae)

The swallowtail butterfly, Sericinus montelus Gray, is endemic to East Asia, has high ornamental value but faces an increased risk of extinction. To understand the overwintering strategies of this species, the dynamic changes in supercooling point (SCP) and water and biochemical contents of diapause-destined and non-diapause S. montelus pupae were investigated. The SCP of laboratory-reared diapause pupae was as low as -26°C compared to -24°C in diapause pupae in the field. Although there was no significant difference in total water content between diapause-destined and non-diapause pupae, the free water of diapause-destined pupae was significantly lower, and the bound water was significantly higher, than that of non-diapause pupae. Lipid, glycogen, and protein contents of diapause-destined pupae showed a downward trend, whereas the total sugar content showed the opposite trend after pupation. The glycogen content decreased rapidly during the initial stage of pupation, whereas the lipid content decreased significantly after 30 days of pupation, suggesting that diapause-destined pupae deplete glycogen stores during the pre-diapause period and then switch to using lipids during the diapause maintenance phase. Trehalose levels in diapause-destined pupae increased significantly and remained high after pupation. Meanwhile, the trehalose content of overwintering pupae during the diapause maintenance period was significantly higher than that of diapause termination pupae in the field. These results suggest that trehalose is the main cryoprotectant for overwintering pupae. Thus, diapausing S. montelus pupae appear to be freeze avoidant, accumulate trehalose as a cryoprotectant, and reduce the free water content to decrease the SCP, enhancing their cold tolerance.

Molecular insights into high-altitude adaption and acclimatisation of Aporrectodea caliginosa

A megabase genome assembly for Aporrectodea caliginosa is presented with transcriptomic and SNP-based evidence for acclimatisation and adaption to extreme weather conditions found at high altitude.

Here, we explore the high-altitude adaptions and acclimatisation of Aporrectodea caliginosa. Population diversity is assessed through mitochondrial barcoding, identifying closely related populations across the island of Pico (Azores). We present the first megabase N50 assembly size (1.2 Mbp) genome for A. caliginosa. High- and low-altitude populations were exposed experimentally to a range of oxygen and temperature conditions, simulating altitudinal conditions, and the transcriptomic responses explored. SNP densities are assessed to identify signatures of selective pressure and their link to differentially expressed genes. The high-altitude A. caliginosa population had lower differential expression and fewer co-expressed genes between conditions, indicating a more condition-refined epigenetic response. Genes identified as under adaptive pressure through F_st and nucleotide diversity in the high-altitude population clustered around the differentially expressed an upstream environmental response control gene, HMGB1. The high-altitude population of A. caliginosa indicated adaption and acclimatisation to high-altitude conditions and suggested resilience to extreme weather events. This mechanistic understanding could help offer a strategy in further identifying other species capable of maintaining soil fertility in extreme environments.

A quantitative synthesis of and predictive framework for studying winter warming effects in reptiles

Increases in temperature related to global warming have important implications for organismal fitness. For ectotherms inhabiting temperate regions, ‘winter warming’ is likely to be a key source of the thermal variation experienced in future years. Studies focusing on the active season predict largely positive responses to warming in the reptiles; however, overlooking potentially deleterious consequences of warming during the inactive season could lead to biased assessments of climate change vulnerability. Here, we review the overwinter ecology of reptiles, and test specific predictions about the effects of warming winters, by performing a meta-analysis of all studies testing winter warming effects on reptile traits to date. We collated information from observational studies measuring responses to natural variation in temperature in more than one winter season, and experimental studies which manipulated ambient temperature during the winter season. Available evidence supports that most reptiles will advance phenologies with rising winter temperatures, which could positively affect fitness by prolonging the active season although effects of these shifts are poorly understood. Conversely, evidence for shifts in survivorship and body condition in response to warming winters was equivocal, with disruptions to biological rhythms potentially leading to unforeseen fitness ramifications. Our results suggest that the effects of warming winters on reptile species are likely to be important but highlight the need for more data and greater integration of experimental and observational approaches. To improve future understanding, we recap major knowledge gaps in the published literature of winter warming effects in reptiles and outline a framework for future research.

Lessons from nature: Leveraging the freeze-tolerant wood frog as a model to improve organ cryopreservation and biobanking

The freeze-tolerant wood frog, Rana sylvatica, is one of the very few vertebrate species known to endure full body freezing in winter and thaw in early spring without any significant sign of damage. Once frozen, wood frogs show no cardiac or lung activity, brain function, or physical movement yet resume full physiological and biochemical functions within hours after thawing. The miraculous ability to tolerate such extreme stresses makes wood frogs an attractive model for identifying the molecular mechanisms that can promote freeze/thaw endurance. Recapitulating these pro-survival strategies in transplantable human cells and organs could improve viability post-thaw leading to better post-transplant outcomes, in addition to providing more time for adequate distribution of these transplantable materials across larger geographical areas. Indeed, several laboratories are beginning to mimic the pro-survival responses observed in wood frogs to preservation of human cells, tissues and organs and, to date, a few trials have been successful in extending preservation time prior to transplantation. In this review, we discuss the biology of the freeze-tolerant wood frog, current advances in biobanking based on these animals, and extend our discussion to future prospects for cryopreservation as an aid to regenerative medicine.

RAGE management: ETS1- EGR1 mediated transcriptional networks regulate angiogenic factors in wood frogs

Freeze-tolerant species, such as wood frogs (Rana sylvatica), are susceptible to multiple co-occurring stresses that they must overcome to survive. Freezing is accompanied by mechanical stress and dehydration due to ice crystal formation in the extracellular space, ischemia/anoxia due to interruption in blood flood, and hyperglycemia due to cryoprotective measures. Wood frogs can survive dehydration, anoxia, and high glucose stress independently of freezing, thereby creating a multifactorial model for studying freeze-tolerance. Oxidative stress and high glucose levels favors the production of pro-oxidant molecules and advanced glycation end product (AGE) adducts that could cause substantial cellular damage. In this study, the involvement of the high mobility group box 1 (HMGB1)-AGE/RAGE (receptor for AGE) axis and the regulation of ETS1 and EGR1-mediated angiogenic responses were investigated in liver of wood frogs expose to freeze/thaw, anoxia/reoxygenation and dehydration/rehydration treatments. HMGB1 and not AGE-adducts are likely to induce the activation of ETS1 and EGR1 via the RAGE pathway. The increase in nuclear localization of both ETS1 and EGR1, but not DNA binding activity in response to stress hints to a potential spatial and temporal regulation in inducing angiogenic factors. Freeze/thaw and dehydration/rehydration treatments increase the levels of both pro- and anti-angiogenic factors, perhaps to prepare for the distribution of cryoprotectants or enable the repair of damaged capillaries and wounds when needed. Overall, wood frogs appear to anticipate the need for angiogenesis in response to freezing and dehydration but not anoxic treatments, probably due to mechanical stress associated with the two former conditions.

Hibernation with Rhythmicity in the Retina, Brain, and Plasma but Not in the Liver of Hibernating Giant Spiny Frogs (Quasipaa spinosa)

Simple Summary

Aquatic ectotherms experience hypoxia under water during hibernation, which enables them to move denoting some level of consciousness, unlike terrestrial hibernators. However, how aquatic ectotherms modulate their clocks and clock-controlled genes in different tissues and plasma melatonin and corticosterone in light-dark cycles under natural environments before and during hibernation, remains to be largely unexplored. To achieve these, in this study, we investigated circadian clock genes, circadian clock-controlled genes, antioxidant enzyme genes, and related hormones in giant spiny frog (Quasipaa spinosa). Our results demonstrated that, despite the hypometabolic state of hibernation, the retina and the brain displayed some circadian rhythms of clock and antioxidant genes, as well as melatonin, while the liver was inactive. These novel findings may contribute to an understanding of how aquatic ectotherms use their circadian system differentially to modulate their physiology in escaping hypoxia during hibernation and preparing for arousal.

Abstract

Hibernation in ectotherms is well known, however, it is unclear how the circadian clock regulates endocrine and antioxidative defense systems of aquatic hibernators. Using the giant spiny frog (Quasipaa spinosa), we studied mRNA expression levels of (1) circadian core clock (Bmal1, Clock, Cry1 and Per2), clock-controlled (Ror-α, Mel-1c and AANAT), and antioxidant enzyme (AOE) (SOD1, SOD2, CAT and GPx) genes in retina, brain, and liver; and (2) plasma melatonin (MT) and corticosterone (CORT) levels, over a 24-hour period at six intervals pre-hibernation and during hibernation. Our results showed that brain Bmal1, Cry1, Per2 and Mel-1c were rhythmic pre-hibernation and Clock and Ror-α during hibernation. However, the retina Bmal1, Clock and Mel-1c, and plasma MT became rhythmic during hibernation. All brain AOEs (SOD1, SOD2, CAT and GPx) were rhythmic pre-hibernation and became non-rhythmic but upregulated, except SOD1, during hibernation. However, plasma CORT and liver clocks and AOEs were non-rhythmic in both periods. The mRNA expression levels of AOEs closely resembled those of Ror-α but not plasma MT oscillations. In the hibernating aquatic frogs, these modulations of melatonin, as well as clock and clock-controlled genes and AOEs might be fundamental for them to remain relatively inactive, increase tolerance, and escape hypoxia, and to prepare for arousal.

Microclimate-driven trends in spring-emergence phenology in a temperate reptile (Vipera berus): Evidence for a potential "climate trap"?

Climate change can not only increase the exposure of organisms to higher temperatures but can also drive phenological shifts that alter their susceptibility to conditions at the onset of breeding cycles. Organisms rely on climatic cues to time annual life cycle events, but the extent to which climate change has altered cue reliability remains unclear. Here, we examined the risk of a "climate trap"-a climatically driven desynchronization of the cues that determine life cycle events and fitness later in the season in a temperate reptile, the European adder (Vipera berus). During the winter, adders hibernate underground, buffered against subzero temperatures, and re-emerge in the spring to reproduce. We derived annual spring-emergence trends between 1983 and 2017 from historical observations in Cornwall, UK, and related these trends to the microclimatic conditions that adders experienced. Using a mechanistic microclimate model, we computed below- and near-ground temperatures to derive accumulated degree-hour and absolute temperature thresholds that predicted annual spring-emergence timing. Trends in annual-emergence timing and subsequent exposure to ground frost were then quantified. We found that adders have advanced their phenology toward earlier emergence. Earlier emergence was associated with increased exposure to ground frost and, contradicting the expected effects of macroclimate warming, increased post-emergence exposure to ground frost at some locations. The susceptibility of adders to this "climate trap" was related to the rate at which frost risk diminishes relative to advancement in phenology, which depends on the seasonality of climate. We emphasize the need to consider exposure to changing microclimatic conditions when forecasting biological impacts of climate change.

Biochemical Response to Freezing in the Siberian Salamander Salamandrella keyserlingii

Simple Summary

The Siberian salamander is a unique amphibian that is capable to survive long-term freezing at −55 °C. We used ¹H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of the Siberian salamander in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with high levels of nucleotide degradation products. There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.

Abstract

The Siberian salamander Salamandrella keyserlingii Dybowski, 1870 is a unique amphibian that is capable to survive long-term freezing at −55 °C. Nothing is known on the biochemical basis of this remarkable freezing tolerance, except for the fact that it uses glycerol as a low molecular weight cryoprotectant. We used ¹H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of S. keyserlingii in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in ischemia manifested as increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with reduced adenosine phosphate pool and high levels of nucleotide degradation products (hypoxanthine, β-alanine, and β-aminoisobutyrate). There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.

Senescence as a trade-off between successful land colonisation and longevity: critical review and analysis of a hypothesis

BACKGROUND

Most common terrestrial animal clades exhibit senescence, suggesting strong adaptive value of this trait. However, there is little support for senescence correlated with specific adaptations. Nevertheless, insects, mammals, and birds, which are the most common terrestrial animal clades that show symptoms of senescence, evolved from clades that predominantly did not show symptoms of senescence. Thus, we aimed to examine senescence in the context of the ecology and life histories of the main clades of animals, including humans, and to formulate hypotheses to explain the causes and origin of senescence in the major clades of terrestrial animals.

METHODOLOGY

We reviewed literature from 1950 to 2020 concerning life expectancy, the existence of senescence, and the adaptive characteristics of the major groups of animals. We then proposed a relationship between senescence and environmental factors, considering the biology of these groups of animals. We constructed a model showing the phylogenetic relationships between animal clades in the context of the major stages of evolution, distinguishing between senescent and biologically 'immortal' clades of animals. Finally, we synthesised current data on senescence with the most important concepts and theories explaining the origin and mechanisms of senescence. Although this categorisation into different senescent phenotypes may be simplistic, we used this to propose a framework for understanding senescence.

RESULTS

We found that terrestrial mammals, insects, and birds show senescence, even though they likely evolved from non-senescent ancestors. Moreover, secondarily aquatic animals show lower rate of senescence than their terrestrial counterparts. Based on the possible life histories of these groups and the analysis of the most important factors affecting the transition from a non-senescent to senescent phenotype, we conclude that aging has evolved, not as a direct effect, but as a correlated response of selection on developmental strategies, and that this occurred separately within each clade. Adoption of specific life history strategies could thus have far-reaching effects in terms of senescence and lifespan.

CONCLUSIONS

Our analysis strongly suggests that senescence may have emerged as a side effect of the evolution of adaptive features that allowed the colonisation of land. Senescence in mammals may be a compromise between land colonisation and longevity. This hypothesis, is supported by palaeobiological and ecological evidence. We hope that the development of new research methodologies and the availability of more data could be used to test this hypothesis and shed greater light on the evolution of senescence.

Evaluation of the impact of extreme floods on the biodiversity of terrestrial animals

Extreme floods seriously affect the biodiversity of terrestrial animals (birds, mammals, reptiles, amphibians, and insects). The degree of impact depends on many factors, e.g., animal characteristics, natural conditions, and flood characteristics. Previous evaluation methods are not suitable for assessing the impact of floods on the biodiversity of all species in the entire submerged area, nor do they accurately reflect variability in the degree of impact. First, the influencing factors were boiled down to four: ratio of flood duration to survival time of animals in floods (D), ratio of flood depth to plant height (S), migration ability of animals (M), and temperature (T), which are represented by a coefficient I. Then, we proposed a calculation method for I based on the four factors. Third, we proposed the total and average biodiversity impact indices, namely, the TBI and ABI, respectively, indicating the overall and average impacts of floods on biodiversity in the submerged area, with the calculation method considering both the number of species and I. An extreme flood was simulated to obtain the flood parameters. In addition, we analyzed monthly changes in partial influencing factors. Finally, the impact of extreme floods on the biodiversity of terrestrial animals in the submerged area was evaluated monthly, and it was found that (1) TBI and ABI changed with space; (2) the ABI of different animals in descending order were mammals, insects, reptiles, amphibians, and birds; (3) the ABI of different land use types in descending order were cropland, orchard and shrubland, grassland, and forest and for TBI were orchard and shrubland, cropland, forest, and grassland; and (4) the TBI and ABI of different animals and land use types changed over time. The proposed method and indices are suitable for assessing the impact of floods on the biodiversity of any organism in any area.

Decisive Effects of Life Stage on the Gut Microbiota Discrepancy Between Two Wild Populations of Hibernating Asiatic Toads (Bufo gargarizans)

Until now, the effects of driving factors on the gut microbiota of amphibians are still mostly confounded. Due to a long-term fasting, hibernating amphibians are ideal experimental materials to explore this question. In this study, we characterized the small intestine microbiota of adult hibernating Asiatic toads (Bufo gargarizans) collected from two geographical populations using 16S rRNA amplicon sequencing technique and evaluated the effects of non-dietary factors (e.g., sex and host genetic background). Proteobacteria (0.9196 ± 0.0892) was characterized as the most dominant phylum in the small gut microbiota of hibernating Asiatic toads, among which five core OTUs were identified and three were classified into Pseudomonas. In view of the coincidence between the dominant KEGG pathways (such as the two-component system) and Pseudomonas, Pseudomonas appeared to be a key adaptor for small gut microbiota during hibernation. Furthermore, we detected a greater discrepancy of gut microbiota between geographical populations than between sexes. Both sex and host genetic background showed a minor effect on the gut microbiota variation. Finally, life stage was determined to be the decisive factor driving the gut microbiota discrepancy between populations. However, a large proportion of the gut microbiota variation (∼70%) could not be explained by the measured deterministic factors (i.e., sex, location, body length, and routine blood indices). Therefore, other factors and/or stochastic processes may play key roles in shaping gut bacterial community of hibernating amphibians.

Freeze tolerance in neotropical frogs: an intrageneric comparison using Pristimantis species of high elevation and medium elevation

Paramos are high-elevation tropical Andean ecosystems above the tree line that display variable temperature and frequent freezing spells. Because a significant anuran community lives in this environment, physiological protection against freezing must characterise individuals in this community. Antifreeze protection has been studied in amphibians from other communities, and it is likely that Paramo anurans rely on the same underlying molecules that convey such protection to Nearctic species. However, given the pervasive presence of freezing spells in the Paramos year-round, the processes of activating protection mechanisms may differ from that of seasonal counterparts. Accordingly, this study investigated cryoprotection strategies in high-elevation tropical frogs, using as a model the terrestrial and nocturnal genus Pristimantis, specifically P. bogotensis, P. elegans and P. nervicus from Paramos, and the warm ecosystem counterparts P. insignitus, P. megalops and P. sanctaemartae. We focused on freeze tolerance and its relationship with glucose accumulation and ice formation. Under field conditions, the highest elevation P. nervicus exhibited higher glucose concentration at dawn compared to noon (1.7 ± 0.6 mmol/L versus 3.5 ± 1.32 mmol/L). Under experimental thermal freeze exposure for 2 hours between −2 and −4 ºC, the glucose concentration of the three Paramo species increased but physiological diversity was evident (P. nervicus 126%; P. bogotensis 100%; and P. elegans 55%). During this test, body ice formation was assessed calorimetrically. The species with the highest body ice formation was P. bogotensis (17% ± 5.37; maximum value: 63%; n = 8), followed by P. nervicus (5% ± 3.27; maximum value: 11%; n = 5) and P. elegans (0.34% ± 0.09; maximum value: 1%; n = 4). The study shows physiological diversity both within a genus and across the amphibian community around the freezing contour. Overall, Paramo species differ in freezing physiology from their low-elevation counterparts. Thus, climate shifts increasing freezing spells may affect the structure of communities in this zone.

Tropicalization of temperate ecosystems in North America: The northward range expansion of tropical organisms in response to warming winter temperatures

Tropicalization is a term used to describe the transformation of temperate ecosystems by poleward-moving tropical organisms in response to warming temperatures. In North America, decreases in the frequency and intensity of extreme winter cold events are expected to allow the poleward range expansion of many cold-sensitive tropical organisms, sometimes at the expense of temperate organisms. Although ecologists have long noted the critical ecological role of winter cold temperature extremes in tropical-temperate transition zones, the ecological effects of extreme cold events have been understudied, and the influence of warming winter temperatures has too often been left out of climate change vulnerability assessments. Here, we examine the influence of extreme cold events on the northward range limits of a diverse group of tropical organisms, including terrestrial plants, coastal wetland plants, coastal fishes, sea turtles, terrestrial reptiles, amphibians, manatees, and insects. For these organisms, extreme cold events can lead to major physiological damage or landscape-scale mass mortality. Conversely, the absence of extreme cold events can foster population growth, range expansion, and ecological regime shifts. We discuss the effects of warming winters on species and ecosystems in tropical-temperate transition zones. In the 21st century, climate change-induced decreases in the frequency and intensity of extreme cold events are expected to facilitate the poleward range expansion of many tropical species. Our review highlights critical knowledge gaps for advancing understanding of the ecological implications of the tropicalization of temperate ecosystems in North America.

High Sub-Zero Organ Preservation: A Paradigm of Nature-Inspired Strategies

The field of organ preservation is filled with advancements that have yet to see widespread clinical translation, with some of the more notable strategies deriving their inspiration from nature. While static cold storage (SCS) at 2 °C to 4 °C is the current state-of-the-art, it contributes to the current shortage of transplantable organs due to the limited preservation times it affords combined with the limited ability of marginal grafts (i.e. those at risk for post-transplant dysfunction or primary non-function) to tolerate SCS. The era of storage solution optimization to minimize SCS-induced hypothermic injury has plateaued in its improvements, resulting in a shift towards the use of machine perfusion systems to oxygenate organs at normothermic, sub-normothermic, or hypothermic temperatures, as well as the use of sub-zero storage temperatures to leverage the protection brought forth by a reduction in metabolic demand. Many of the rigors that organs are subjected to at low sub-zero temperatures (-80 °C to -196 °C) commonly used for mammalian cell preservation have yet to be surmounted. Therefore, this article focuses on an intermediate temperature range (0 °C to -20 °C), where much success has been seen in the past two decades. The mechanisms leveraged by organisms capable of withstanding prolonged periods at these temperatures through either avoiding or tolerating the formation of ice has provided a foundation for some of the more promising efforts. This article therefore aims to contextualize the translation of these strategies into the realm of mammalian organ preservation.

Expanded Supercooling Capacity With No Cryoprotectant Accumulation Underlies Cold Tolerance of the European Grapevine Moth

The European grapevine moth, Lobesia botrana (Denis et Schiffermuller), is a serious invasive pest that causes significant losses to the flowers and fruits of grapes in most of the world. This multivoltine pest passes the winter as the third-generation diapausing pupa. The current study was designed to compare nondiapausing (first and second generations) and diapausing pupae (third generation) and to investigate the relationship among cold tolerance, the supercooling point (SCP), and diapause development of the third-generation diapausing pupae. The lethal temperatures (LTs) for the three generations were determined using 24-h exposure at subzero temperatures. The mean SCP of the pupae was estimated at approx. -22.6°C, the lowest level of which (-23.7°C) was recorded in the well-developed diapausing pupae in February. The highest level of cold tolerance was also recorded in February. There were no significant differences among the temperatures required to kill 30, 50, and 90% of the pupae. The temperatures significantly decreased from October onward and reached the lowest levels in February during which the lowest SCP and the highest cold tolerance were observed in the diapausing pupae. No significant differences were found in the cryoprotectant levels, among the diapausing and nondiapausing pupae, and the diapause development. The highest activity of cAMP-dependent protein kinase (AMPK) was recorded in the late diapause in February. The findings suggested a relationship among SCP depression, cold tolerance enhancement, and diapause development. A bimodal cold-tolerance strategy (freeze-intolerant and freeze-tolerant) was found to be a feature of the pupae.

Response of Anatolian mountain frogs (Rana macrocnemis and Rana holtzi) to freezing, anoxia, and dehydration: Glucose as a cryoprotectant

Cryoprotectants play an essential role in the survival of some amphibians in response to different stress conditions such as freezing, anoxia, and dehydration. Glucose is one of the cryoprotectants important for freeze-tolerant frogs. The aim of the present study was to investigate the survival strategies of Anatolian mountain frogs (Rana macrocnemis and Rana holtzi), which are terrestrial hibernators, by examining the changes in glucose and water content in some tissues at subzero temperatures. In the current study, animals were exposed to freezing (-2.5 °C), anoxia, and dehydration treatments. During these treatments, all frogs survived. The glucose levels in the plasma, liver, and skeletal muscle and the water content of the tissues were measured during the freezing, anoxia, and dehydration. Changes in body weight were also recorded in both species. During the freezing, a 3.3-fold increase was seen in the blood glucose level of R. macrocnemis (1.35 ± 0.25 to 4.45 ± 0.51 μmol mL^-1), whereas the blood glucose level of R. holtzi exhibited a 4.5-fold increase (1.90 ± 0.25 to 8.67 ± 2.22 μmol mL^-1). In the liver, a 6.7-fold increase was seen in the glucose level of R. macrocnemis (5.66 ± 0.15 to 38.27 ± 8.53 μmol g^-1) and the increase in R. holtzi was approximately 6.0-fold (2.25 ± 0.46 to 13.36 ± 1.32 μmol g^-1) during freezing. The liver glucose levels of both species also increased significantly in response to the anoxia and dehydration. In both species, the glucose levels of the skeletal muscle were found to be higher in dehydration than with freezing and anoxia. In conclusion, our results suggest that glucose may be identified as an important cryoprotectant that plays an important role in the survival of Anatolian mountain frogs during extreme conditions.

Future winters present a complex energetic landscape of decreased costs and reduced risk for a freeze-tolerant amphibian, the Wood Frog (Lithobates sylvaticus)

Winter climate warming is rapidly leading to changes in snow depth and soil temperatures across mid- and high-latitude ecosystems, with important implications for survival and distribution of species that overwinter beneath the snow. Amphibians are a particularly vulnerable group to winter climate change because of the tight coupling between their body temperature and metabolic rate. Here, we used a mechanistic microclimate model coupled to an animal biophysics model to predict the spatially explicit effects of future climate change on the wintering energetics of a freeze-tolerant amphibian, the Wood Frog (Lithobates sylvaticus), across its distributional range in the eastern United States. Our below-the-snow microclimate simulations were driven by dynamically downscaled climate projections from a regional climate model coupled to a one-dimensional model of the Laurentian Great Lakes. We found that warming soil temperatures and decreasing winter length have opposing effects on Wood Frog winter energy requirements, leading to geographically heterogeneous implications for Wood Frogs. While energy expenditures and peak body ice content were predicted to decline in Wood Frogs across most of our study region, we identified an area of heightened energetic risk in the northwestern part of the Great Lakes region where energy requirements were predicted to increase. Because Wood Frogs rely on body stores acquired in fall to fuel winter survival and spring breeding, increased winter energy requirements have the potential to impact local survival and reproduction. Given the geographically variable and intertwined drivers of future under-snow conditions (e.g., declining snow depths, rising air temperatures, shortening winters), spatially explicit assessments of species energetics and risk will be important to understanding the vulnerability of subnivium-adapted species.

Freeze tolerance and the underlying metabolite responses in the Xizang plateau frog, Nanorana parkeri

The frog Nanorana parkeri (Dicroglossidae) is endemic to the Tibetan Plateau, and overwinters shallow pond within damp caves for up to 6 months. Herein, we investigate the freeze tolerance of this species and profile changes in liver and skeletal muscle metabolite levels using an untargeted LC-MS-based metabolomic approach to investigate molecular mechanisms that may contribute to freezing survival. We found that three of seven specimens of N. parkeri could survive after being frozen for 12 h at - 2.0 °C with 39.91% ± 5.4% (n = 7) of total body water converted to ice. Freezing exposure induced partial dehydration of the muscle, which contributed to decreasing the amount of freezable water within the muscle and could be protective for the myocytes themselves. A comparative metabolomic analysis showed that freezing elicited significant responses, and a total of 33 and 36 differentially expressed metabolites were identified in the liver and muscle, respectively. These metabolites mainly participate in alanine, aspartic acid and glutamic acid metabolism, arginine and proline metabolism, and D-glutamine and D-glutamate metabolism. After freezing exposure, the contents of ornithine, melezitose, and maltotriose rose significantly; these may act as cryoprotectants. Additionally, the content of 8-hydroxy-2-deoxyguanine, 7-Ketocholesterol and hypoxanthine showed a marked increase, suggesting that freezing induced oxidative stress in the frogs. In summary, N. parkeri can tolerate a brief and partial freezing of their body, which was accompanied by substantial changes in metabolomic profiles after freezing exposure.

MondoA:MLX complex regulates glucose-dependent gene expression and links to circadian rhythm in liver and brain of the freeze-tolerant wood frog, Rana sylvatica

The wood frog, Rana sylvatica, is one of only a few vertebrate species that display natural freeze tolerance. Frogs survive the freezing of about two-thirds of their body water as extracellular ice over the winter months. Multiple adaptations support freeze tolerance including metabolic rate depression and the production of huge amounts of glucose (often 200 mM or more) as a cryoprotectant that protects cells from freeze damage. To understand how high glucose levels affect gene expression, we studied MondoA, a glucose sensing transcription factor, and its partner MLX (Max-like protein) to assess their ability to modulate the expression of genes involved in glucose metabolism and circadian rhythm. Wood frog liver and brain tissues were analyzed, assessing protein levels, nuclear distribution, and DNA binding activity of MondoA:MLX during freezing (24 h at - 2.5 °C) and subsequent thawing (8 h returned to 5 °C), as compared with 5 °C controls. Downstream targets of MondoA:MLX were also evaluated: TXNIP (thioredoxin interacting protein), ARRDC4 (arrestin domain containing 4), HK-2 (hexokinase-2), PFKFB-3 (6-phosphofructo-2-kinase isozyme 3) and KLF-10 (Kruppel-like factor-10). Both KLF-10 and PFKFB-3 are also involved in circadian dependant regulation which was also explored in the current study via analysis of BMAL-1 (aryl hydrocarbon receptor nuclear translocator-like protein 1) and CLOCK (circadian locomotor output cycles kaput) proteins. Our data establish the MondoA-MLX complex as active under the hyperglycemic conditions in liver to regulate glucose metabolism and may also link to circadian rhythm in liver via KLF-10 and PFKFB-3 but not in brain.

Overwintering Physiology and Cold Tolerance of the Sunn Pest, Eurygaster integriceps, an Emphasis on the Role of Cryoprotectants

As a serious pest of wheat, the Sunn pest, Eurygaster integriceps Puton (Hem.: Scutelleridae), is prevalent in Iran. This pest belongs to univoltine species and tends to estivate and overwinter in high altitudes of nearby mountains as diapausing adults. The economic importance of the crop was attacked by this pest, i.e., wheat led the authors to study the physiological adaptations of these diapausing adults, that is, changes in the supercooling point (SCP), in the accumulation of cryoprotectants, and in the activities of the related enzymes in relation to diapause development. The mean SCP of the diapausing adults was found to be −8°C. The lowest SCP, i.e., approximately −11°C, was observed in the middle of diapause, October, when the highest cold hardiness was also interestingly recorded. This finding proposed that SCP depression could be a feasible cold-tolerance strategy for diapausing adults. The sugar content was high in the initiation and at the termination of diapause and was low during diapause maintenance. These sugar reserves were most likely utilized to be converted to glycogen and lipid during diapause maintenance as a survival strategy. The changes in the glycogen and lipid contents were inversely proportional to the changes in the total sugar content. The authors also found that the changes in the glycogen content were directly proportional to those in the low-molecular-weight carbohydrates (e.g., glycerol and trehalose) and in the diapause development. This finding underlined the role of the low-molecular-weight carbohydrates, such as the cryoprotectants, in enhancing the cold tolerance of the given insect. In this study, the diapause-associated changes in the activities of α-amylases and proteases were also investigated. The results showed that the enzyme activities were related to diapause development and cold-tolerance enhancement. The highest enzyme activity was observed in September. Since the overwintering adults of the Sunn pest could not tolerate temperatures below their SCPs, they were grouped in the freeze-intolerant species.

Metabolic characteristics of overwintering by the high-altitude dwelling Xizang plateau frog, Nanorana parkeri

The Xizang plateau frog, Nanorana parkeri, has the highest altitudinal distribution of all frogs in the world and survives the cold of winter without feeding by entering into a hibernating state. However, little attention has been paid to its physiological and biochemical characteristics that support overwintering underwater in small ponds. Here, we measured metabolic rate and heart rate, and collected liver and muscle samples from N. parkeri in summer and winter for analysis of mitochondrial respiration rate, and activities and relative mRNA transcript expression of metabolic enzymes. Compared with summer-collected frogs, both resting metabolic rate and heart rate were significantly reduced in winter-collected frogs. Both state 3 and state 4 respiration of liver mitochondria were also significantly reduced in winter but muscle mitochondria showed a decline only in state 3 respiration in winter. The activities and corresponding mRNA expression of cytochrome c oxidase showed a marked decline in winter, whereas the activities and corresponding mRNA expression of lactate dehydrogenase increased in winter-collected frogs, compared to summer. The thermal sensitivity (Q₁₀ values) for state 3 respiration rate by liver mitochondria, and activities of lactate dehydrogenase, and cytochrome c oxidase all increased in winter-collected frogs, compared with summer frogs, suggesting that overwintering frogs were more sensitive to changes in external temperature. Enzyme changes mainly result from lower overall quantities of these enzymes as well as post-translational modifications. We conclude that overwintering N. parkeri exhibit a seasonal, temperature-independent suppression of metabolism that is mediated at multiple levels: physiological, mitochondrial, gene expression and enzyme activity levels.

Hepatic transcriptome of the freeze-tolerant Cope's gray treefrog, Dryophytes chrysoscelis: responses to cold acclimation and freezing

Background

Cope’s gray treefrog, Dryophytes chrysoscelis, withstands the physiological challenges of corporeal freezing, partly by accumulating cryoprotective compounds of hepatic origin, including glycerol, urea, and glucose. We hypothesized that expression of genes related to cryoprotectant mobilization and stress tolerance would be differentially regulated in response to cold. Using high-throughput RNA sequencing (RNA-Seq), a hepatic transcriptome was generated for D. chrysoscelis, and gene expression was compared among frogs that were warm-acclimated, cold-acclimated, and frozen.

Results

A total of 159,556 transcripts were generated; 39% showed homology with known transcripts, and 34% of all transcripts were annotated. Gene-level analyses identified 34,936 genes, 85% of which were annotated. Cold acclimation induced differential expression both of genes and non-coding transcripts; freezing induced few additional changes. Transcript-level analysis followed by gene-level aggregation revealed 3582 differentially expressed genes, whereas analysis at the gene level revealed 1324 differentially regulated genes. Approximately 3.6% of differentially expressed sequences were non-coding and of no identifiable homology. Expression of several genes associated with cryoprotectant accumulation was altered during cold acclimation. Of note, glycerol kinase expression decreased with cold exposure, possibly promoting accumulation of glycerol, whereas glucose export was transcriptionally promoted by upregulation of glucose-6-phosphatase and downregulation of genes of various glycolytic enzymes. Several genes related to heat shock protein response, DNA repair, and the ubiquitin proteasome pathway were upregulated in cold and frozen frogs, whereas genes involved in responses to oxidative stress and anoxia, both potential sources of cellular damage during freezing, were downregulated or unchanged.

Conclusion

Our study is the first to report transcriptomic responses to low temperature exposure in a freeze-tolerant vertebrate. The hepatic transcriptome of Dryophytes chrysoscelis is responsive to cold and freezing. Transcriptomic regulation of genes related to particular pathways, such as glycerol biosynthesis, were not all regulated in parallel. The physiological demands associated with cold and freezing, as well as the transcriptomic responses observed in this study, are shared with several organisms that face similar ecophysiological challenges, suggesting common regulatory mechanisms. The role of transcriptional regulation relative to other cellular processes, and of non-coding transcripts as elements of those responses, deserve further study.

Ice Binding Proteins: Diverse Biological Roles and Applications in Different Types of Industry

More than 80% of Earth’s surface is exposed periodically or continuously to temperatures below 5 °C. Organisms that can live in these areas are called psychrophilic or psychrotolerant. They have evolved many adaptations that allow them to survive low temperatures. One of the most interesting modifications is production of specific substances that prevent living organisms from freezing. Psychrophiles can synthesize special peptides and proteins that modulate the growth of ice crystals and are generally called ice binding proteins (IBPs). Among them, antifreeze proteins (AFPs) inhibit the formation of large ice grains inside the cells that may damage cellular organelles or cause cell death. AFPs, with their unique properties of thermal hysteresis (TH) and ice recrystallization inhibition (IRI), have become one of the promising tools in industrial applications like cryobiology, food storage, and others. Attention of the industry was also caught by another group of IBPs exhibiting a different activity—ice-nucleating proteins (INPs). This review summarizes the current state of art and possible utilizations of the large group of IBPs.

Predicting the potential distribution of Amblyomma americanum (Acari: Ixodidae) infestation in New Zealand, using maximum entropy-based ecological niche modelling

Although currently exotic to New Zealand, the potential geographic distribution of Amblyomma americanum (L.), the lone star tick, was modelled using maximum entropy (MaxEnt). The MaxEnt model was calibrated across the native range of A. americanum in North America using present-day climatic conditions and occurrence data from museum collections. The resulting model was then projected onto New Zealand using both present-day and future climates modelled under two greenhouse gas emission scenarios, representative concentration pathways (RCP) 4.5 (low) and RCP 8.5 (high). Three sets of WorldClim bioclimatic variables were chosen using the jackknife method and tested in MaxEnt using different combinations of model feature class functions and regularization multiplier values. The preferred model was selected based on partial receiver operating characteristic tests, the omission rate and the lowest Akaike information criterion. The final model had four bioclimatic variables, Annual Mean Temperature (BIO₁), Annual Precipitation (BIO₁₂), Precipitation Seasonality (BIO₁₅) and Precipitation of Driest Quarter (BIO₁₇), and the projected New Zealand distribution was broadly similar to that of Haemaphysalis longicornis Neumann, New Zealand's only livestock tick, but with a more extensive predicted suitability. The climate change predictions for the year 2050 under both low and high RCP scenarios projected only moderate increases in habitat suitability along the mountain valleys in the South Island. In conclusion, this analysis shows that given the opportunity and license A. americanum could and would successfully establish in New Zealand and could provide another vector for theileriosis organisms.

Me2SO- and serum-free cryopreservation of human umbilical cord mesenchymal stem cells using electroporation-assisted delivery of sugars

Cryopreservation is the universal technology used to enable long-term storage and continuous availability of cell stocks and tissues for regenerative medicine demands. The main components of standard freezing media are dimethyl sulfoxide (hereinafter Me₂SO) and fetal bovine serum (FBS). However, for manufacturing of cells and tissue-engineered products in accordance with the principles of Good Manufacturing Practice (GMP), current considerations in regenerative medicine suggest development of Me₂SO- and serum-free biopreservation strategies due to safety concerns over Me₂SO-induced side effects and immunogenicity of animal serum. In this work, the effect of electroporation-assisted pre-freeze delivery of sucrose, trehalose and raffinose into human umbilical cord mesenchymal stem cells (hUCMSCs) on their post-thaw survival was investigated. The optimal strength of electric field at 8 pulses with 100 μs duration and 1 Hz pulse repetition frequency was determined to be 1.5 kV/cm from permeabilization (propidium iodide uptake) vs. cell recovery data (resazurin reduction assay). Using sugars as sole cryoprotectants with electroporation, concentration-dependent increase in cell survival was observed. Irrespective of sugar type, the highest cell survival (up to 80%) was achieved at 400 mM extracellular concentration and electroporation. Cell freezing without electroporation yielded significantly lower survival rates. In the optimal scenario, cells were able to attach 24 h after thawing demonstrating characteristic shape and sugar-loaded vacuoles. Application of 10% Me₂SO/90% FBS as a positive control provided cell survival exceeding 90%. Next, high glass transition temperatures determined for optimal concentrations of sugars by differential scanning calorimetry (DSC) suggest the possibility to store samples at -80 °C. In summary, using electroporation to incorporate cryoprotective sugars into cells is an effective strategy towards Me₂SO- and serum-free cryopreservation and may pave the way for further progress in establishing clinically safe biopreservation strategies for efficient long-term biobanking of cells.

Adaptation of the Andean Toad Rhinella spinulosa (Anura: Bufonidae) at Low Temperatures: The Role of Glucose as Cryoprotectant

We studied the role of plasma glucose concentration on individuals of Rhinella spinulosa in response to annual temperature variation and freezing temperatures. Measurements and collection of toads were made every 2 mo for a period of 1 yr. To determine whether toads were exposed to low temperatures in their habitat, we proceeded with the study of operating temperatures (T _e). The measures of operating temperature were determined by using plaster models placed in the field, simulating the situation where toads are outside or inside shelters, for which it was determined that individuals in the winter season would have been exposed to temperatures below 0°C. Glucose levels measured in field specimens showed an annual variation, but laboratory specimens exposed to freezing temperatures had higher plasma glucose levels than field toads. Furthermore, the crystallization temperature for the species has been recorded at -1.6°C. The increase in glucose concentration indicates its possible use as a cryoprotectant before freezing events in this species of frogs and also in the coldest months at temperatures below 0°C.

Overwintering adaptations and extreme freeze tolerance in a subarctic population of the wood frog, Rana sylvatica

The terrestrially hibernating wood frog (Rana sylvatica) is well-known for its iconic freeze tolerance, an overwintering adaptation that has received considerable investigation over the past 35 years. Virtually, all of this research has concerned frogs indigenous to the temperate regions of its broad range within North America. However, recent investigations have shown that frogs of subarctic populations are extremely cold hardy, being capable of surviving freezing for longer periods and at much lower temperatures as compared to conspecifics from temperate regions. Their exceptional freeze tolerance is partly supported by an enhanced cryoprotectant system that uses very high levels of urea and glucose to limit ice formation, regulate metabolism, and protect macromolecules and cellular structures from freezing/thawing stresses. In the weeks before they begin hibernating, northern frogs undertake radical physiological transitions, such as depletion of fat stores and catabolism of muscle protein, that prime the cryoprotectant system by accruing urea and stockpiling glycogen from which glucose is mobilized during freezing. Concentrations of cryoprotectants ultimately achieved in Alaskan frogs when freezing occurs vary among tissues but generally are higher than those of frogs inhabiting milder climates. This review summarizes the molecular, biochemical, and physiological adaptations permitting this northern phenotype to survive the long and harsh winters of the region.

Ecophysiology of Amphibians: Information for Best Mechanistic Models

Several amphibian lineages epitomize the faunal biodiversity crises, with numerous reports of population declines and extinctions worldwide. Predicting how such lineages will cope with environmental changes is an urgent challenge for biologists. A promising framework for this involves mechanistic modeling, which integrates organismal ecophysiological features and ecological models as a means to establish causal and consequential relationships of species with their physical environment. Solid frameworks built for other tetrapods (e.g., lizards) have proved successful in this context, but its extension to amphibians requires care. First, the natural history of amphibians is distinct within tetrapods, for it includes a biphasic life cycle that undergoes major habitat transitions and changes in sensitivity to environmental factors. Second, the accumulated data on amphibian ecophysiology is not nearly as expressive, is heavily biased towards adult lifeforms of few non-tropical lineages, and overlook the importance of hydrothermal relationships. Thus, we argue that critical usage and improvement in the available data is essential for enhancing the power of mechanistic modeling from the physiological ecology of amphibians. We highlight the complexity of ecophysiological variables and the need for understanding the natural history of the group under study and indicate directions deemed crucial to attaining steady progress in this field.

Nitric oxide metabolites in hypoxia, freezing, and hibernation of the wood frog, Rana sylvatica

Nitric oxide (NO) is a gaseous free radical that in diverse organisms performs many signaling and protective functions, such as vasoregulation, inhibition of apoptosis, antioxidation, and metabolic suppression. Increased availability of NO may be especially important during life-history periods when organisms contend with multiple stresses. We investigated dynamics of the NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-), in the blood plasma, heart, liver, and skeletal muscle of the wood frog (Rana sylvatica), an amphibian that endures chronic cold, freezing, hypoxia, dehydration, and extended aphagia during hibernation. We found elevated concentrations of NO₂^- and/or NO₃^- in the plasma (up to 4.1-fold), heart (3.1-fold), and liver (up to 4.1-fold) of frogs subjected to experimental hypoxia (24 h, 4 °C), and in the liver (up to 3.8-fold) of experimentally frozen frogs (48 h, - 2.5 °C), suggesting that increased NO availability aids in survival of these stresses. During a 38-week period of simulated hibernation, NO₂^- and/or NO₃^- increased in the plasma (up to 10.4-fold), heart (up to 3.3-fold), and liver (5.0-fold) during an initial 5-week winter-acclimatization regimen and generally remained elevated thereafter. In hibernation, plasma NO₂^- was higher in frogs indigenous to Interior Alaska than in conspecifics from a temperate locale (southern Ohio), suggesting that NO availability is matched to the severity of environmental conditions prevailing in winter. The comparatively high NO availability in R. sylvatica, a stress-tolerant species, together with published values for other species, suggest that the NO protection system is of general importance in the stress adaptation of vertebrates.

Phenotypic Plasticity in Animals Exposed to Osmotic Stress - Is it Always Adaptive?

Hyperplasia and hypertrophy are elements of phenotypic plasticity adjusting organ size and function. Because they are costly, we assume that they are beneficial. In this review, the authors discuss examples of tissue and organ systems that respond with plastic changes to osmotic stress to raise awareness that we do not always have sufficient experimental evidence to conclude that such processes provide fitness advantages. Changes in hydranth architecture in the hydroid Cordylophora caspia or variations in size in the anal papillae of insect larvae upon changes in medium salinity may be adaptive or not. The restructuring of salt glands in ducklings upon salt-loading is an example of phenotypic plasticity which indeed seems beneficial. As the genomes of model species are recently sequenced and the animals are easy to rear, these species are suitable study objects to investigate the biological significance of phenotypic plasticity and to study potential epigenetic and other mechanisms underlying phenotypic changes.