The role of polyols and nucleating agents in cold-hardy beetles

Advances in understanding Lepidoptera cold tolerance

Ambient thermal conditions mediate insect growth, development, reproduction, survival, and distribution. With increasingly frequent and severe cold spells, it is critical to determine low-temperature performance and cold tolerances of ecologically and economically essential insect groups to predict their responses to global environmental change. This review covers the cold tolerance strategies of 49 species of Lepidoptera (moths and butterflies), focusing on species that are known as crop pests and crop storage facilities. We synthesize cold tolerance strategies of well-studied species within this order, finding that diapause is a distinctive mechanism that has independently evolved in different genera and families of Lepidoptera. However, the occurrence of diapause in each life stage is specific to the species, and in most studied lepidopteran species, the feeding stage (as larva) is the predominant overwintering stage. We also found that the onset of diapause and the improvement of cold tolerance are interdependent phenomena that typically occur together. Moreover, adopting a cold tolerance strategy is not an inherent, fixed trait and is greatly influenced by a species' geographic distribution and rearing conditions. This review further finds that freeze avoidance rather than freeze tolerance or chill susceptibility is the primary cold tolerance strategy among lepidopteran species. The cold hardiness of lepidopteran insects primarily depends on the accumulation of cryoprotectants and the depression of the supercooling point. We highlight variations in cold tolerance strategies and mechanisms among a subset of Lepidoptera, however, further work is needed to elucidate these strategies for the vast numbers of neglected species and populations to understand broad-scale responses to global change.

Exploring Cold Hardiness within a Butterfly Clade: Supercooling Ability and Polyol Profiles in European Satyrinae

The cold hardiness of overwintering stages affects the distribution of temperate and cold-zone insects. Studies on Erebia, a species-rich cold-zone butterfly genus, detected unexpected diversity of cold hardiness traits. We expanded our investigation to eight Satyrinae species of seven genera. We assessed Autumn and Winter supercooling points (SCPs) and concentrations of putatively cryoprotective sugars and polyols via gas chromatography–mass spectrometry. Aphantopus hyperantus and Hipparchia semele survived freezing of body fluids; Coenonympha arcania, C. gardetta, and Melanargia galathea died prior to freezing; Maniola jurtina, Chazara briseis, and Minois dryas displayed a mixed response. SCP varied from −22 to −9 °C among species. Total sugar and polyol concentrations (TSPC) varied sixfold (2 to 12 μg × mg−1) and eightfold including the Erebia spp. results. SCP and TSPC did not correlate. Alpine Erebia spp. contained high trehalose, threitol, and erythritol; C. briseis and C. gardetta contained high ribitol and trehalose; lowland species contained high saccharose, maltose, fructose, and sorbitol. SCP, TSPC, and glycerol concentrations were affected by phylogeny. Species of mountains or steppes tend to be freeze-avoidant, overwinter as young larvae, and contain high concentrations of trehalose, while those of mesic environments tend to be freeze-tolerant, overwinter as later instars, and rely on compounds such as maltose, saccharose, and fructose.

Climate Mismatch between Introduced Biological Control Agents and Their Invasive Host Plants: Improving Biological Control of Tropical Weeds in Temperate Regions

Simple Summary

Mismatched distributions between biological control agents and their host plants occur for a variety of reasons but are often linked to climate, specifically differences in their low-temperature tolerances. How to measure and use low-temperature tolerances of control agents to inform agent prioritization, selection for redistribution, or predict efficacy is vitally important, but has not been previously synthesized in a single source. We discuss causes of climate mismatches between agents and target weeds, the traditional and non-traditional approaches that could be used to decrease the degree of mismatch and improve control, and regulatory issues to consider when taking such approaches. We also discuss the variety of cold tolerance metrics, their measurement and ecological value, and the types of modeling that can be carried out to improve predictions about potential distributions of agents. We also briefly touch on molecular bases for cold tolerance and opportunities for improving cold tolerance of agents using modern molecular tools.

Abstract

Many weed biological control programs suffer from large-scale spatial variation in success due to restricted distributions or abundances of agents in temperate climates. For some of the world’s worst aquatic weeds, agents are established but overwintering conditions limit their survival in higher latitudes or elevations. The resulting need is for new or improved site- or region-specific biological control tools. Here, we review this challenge with a focus on low-temperature limitations of agents and propose a roadmap for improving success. Investigations across spatial scales, from global (e.g., foreign exploration), to local (selective breeding), to individual organisms (molecular modification), are discussed. A combination of traditional (foreign) and non-traditional (introduced range) exploration may lead to the discovery and development of better-adapted agent genotypes. A multivariate approach using ecologically relevant metrics to quantify and compare cold tolerance among agent populations is likely required. These data can be used to inform environmental niche modeling combined with mechanistic modeling of species’ fundamental climate niches and life histories to predict where, when, and at what abundance agents will occur. Finally, synthetic and systems biology approaches in conjunction with advanced modern genomics, gene silencing and gene editing technologies may be used to identify and alter the expression of genes enhancing cold tolerance, but this technology in the context of weed biological control has not been fully explored.

An open source cryostage and software analysis method for detection of antifreeze activity

The aim of this study is to provide the reader with a simple setup that can detect antifreeze proteins (AFP) by inhibition of ice recrystallisation in very small sample sizes. This includes an open source cryostage, a method for preparing and loading samples as well as a software analysis method. The entire setup was tested using hyperactive AFP from the cerambycid beetle, Rhagium mordax. Samples containing AFP were compared to buffer samples, and the results are visualised as crystal radius evolution over time and in absolute change over 30 min. Statistical analysis showed that samples containing AFP could reliably be told apart from controls after only two minutes of recrystallisation. The goal of providing a fast, cheap and easy method for detecting antifreeze proteins in solution was met, and further development of the system can be followed at https://github.com/pechano/cryostage.

Cold tolerance of the montane Sierra leaf beetle, Chrysomela aeneicollis

Small ectothermic animals living at high altitude in temperate latitudes are vulnerable to lethal cold throughout the year. Here we investigated the cold tolerance of the leaf beetle Chrysomela aeneicollis living at high elevation in California's Sierra Nevada mountains. These insects spend over half their life cycle overwintering, and may therefore be vulnerable to winter cold, and prior studies have demonstrated that survival is reduced by exposure to summertime cold. We identify overwintering microhabitat of this insect, describe cold tolerance strategies in all life stages, and use microclimate data to determine the importance of snow cover and microhabitat buffering for overwinter survival. Cold tolerance varies among life history stages and is typically correlated with microhabitat temperature: cold hardiness is lowest in chill-susceptible larvae, and highest in freeze-tolerant adults. Hemolymph osmolality is higher in quiescent (overwintering) than summer adults, primarily, but not exclusively, due to elevated hemolymph glycerol. In nature, adult beetles overwinter primarily in leaf litter and suffer high mortality if early, unseasonable cold prevents them from entering this refuge. These data suggest that cold tolerance is tightly linked to life stage. Thus, population persistence of montane insects may become problematic as climate becomes more unpredictable and climate change uncouples the phenology of cold tolerance and development from the timing of extreme cold events.

Responses of invertebrates to temperature and water stress: A polar perspective

As small bodied poikilothermic ectotherms, invertebrates, more so than any other animal group, are susceptible to extremes of temperature and low water availability. In few places is this more apparent than in the Arctic and Antarctic, where low temperatures predominate and water is unusable during winter and unavailable for parts of summer. Polar terrestrial invertebrates express a suite of physiological, biochemical and genomic features in response to these stressors. However, the situation is not as simple as responding to each stressor in isolation, as they are often faced in combination. We consider how polar terrestrial invertebrates manage this scenario in light of their physiology and ecology. Climate change is also leading to warmer summers in parts of the polar regions, concomitantly increasing the potential for drought. The interaction between high temperature and low water availability, and the invertebrates' response to them, are therefore also explored.

NATURAL HISTORY, CLASSIFICATION, RECONSTRUCTED PHYLOGENY, AND GEOGRAPHIC HISTORY OF PYTHO LATREILLE (COLEOPTERA: HETEROMERA: PYTHIDAE)

The classification of the nine world species of Pytho Latreille is reviewed by study of adult, larval, and pupal stages. Keys are provided for separation of species in these three life stages. Taxonomic changes (senior synonym in brackets) include synonymy of P. fallax Seidlitz 1916 [= P. niger Kirby 1837]; P. americanus Kirby 1837 [= P. planus (Olivier 1795)]; P. deplanatus Mannerheim 1843 is transferred from a junior subjective synonym of P. depressus (Linnaeus 1767) to a junior subjective synonym of P. planus (Olivier 1795). Lectotype designations are provided for the following: P. seidlitzi Blair 1925; P. nivalis Lewis 1888; P. niger Kirby 1837; P. fallax Seidlitz 1916; P. abieticola J. Sahlberg 1875; and P. americanus Kirby 1837. Eight larval stage, and 12 adult stage characters were selected for cladistic analysis. Lacking out-group material, pupal characters were not analysed. Character states were polarized using a generalized out-group composed of the three other genera of Pythinae (all monobasic). Phylogenetic analysis based on these 18 characters suggests four monophyletic species-groups: P. seidlitzi group (P. seidlitzi Blair — North America); P. kolwensis group (P. strictus LeConte – North America, P. kolwensis C. Sahlberg —Fennoscandia and the U.S.S.R., P. nivalis Lewis — Japan); P. niger group (P. niger Kirby — North America, P. abieticola J. Sahlberg — Europe, P. jezoensis Kôno — Japan); P. depressus group [P. planus (Olivier, 1795) — North America, P. depressus (Linnaeus, 1767) — Europe and the U.S.S.R.]. Larval stage synapomorphies are relatively more important in defining the species-groups than are those of the adult stage. The ancestor of Pythidae may have been associated with Coniferae as early as the Jurassic. The common ancestor of Northern Hemisphere Pythinae became isolated upon Laurasia once separation from Gondwanaland occurred near the end of the Jurassic. Two of the species-groups have similar disjunctions in North America, Europe, and Japan. The relatively eastern distributions of the North American member of each suggests that the ancestor of each species-group was Euramerican, and underwent vicariance with the opening of the North Atlantic in the Middle Cretaceous. The present distribution of both species-groups is thought to have been caused by the same vicariant event. The ancestor of the P. depressus group, which is presently circumboreal, was probably widespread and could have been Asiamerican in distribution. In the middle to late Tertiary, evidence suggests that Beringia was covered with coniferous forest, and the ancestor of the P. depressus group probably extended across this land bridge. Final separation between any North American and European/Asian species occurred in the Late Miocene or Pliocene, when a cooling climate made possible the evolution of treeless tundra in the north.

Do ice nucleating lipoproteins protect frozen insects against toxic chemical agents?

As the body fluid of freeze-tolerant organisms freezes, solutes become concentrated in the gradually smaller unfrozen fluid fraction, and dissolved trace metals may reach toxic levels. A dialysis technique was used to investigate the metal binding capacity of the low density fraction of the hemolymph from the freeze tolerant beetle Phyto depressus. The low density fraction, assumed to contain the ice nucleating lipoproteins, showed approximately 100 times greater capacity to bind metals (Cd (2+), Cu (2+) and Zn (2+)) than the proteins albumin, hemoglobin and similar to metallothionein. The high metal binding capacity in the low density fraction raises the question if the ice nucleating lipoproteins might assist in detoxification of potentially toxic concentrations of metals that may occur when a large fraction of the bodyfluids of freeze tolerant insects freeze. This hypotheis is consistent with the fact that the lipoprotein ice nucleators are present in far greater amounts than required for ice nucleation, and also with the fact that the lipoprotein ice nucleators have a remarkably high content of amino acids with negatively charged residues that may act as metal binding sites.

The overwintering physiology of the emerald ash borer, Agrilus planipennis fairmaire (coleoptera: buprestidae)

Ability to survive cold is an important factor in determining northern range limits of insects. The emerald ash borer (Agrilus planipennis) is an invasive beetle introduced from Asia that is causing extensive damage to ash trees in North America, but little is known about its cold tolerance. Herein, the cold tolerance strategy and mechanisms involved in the cold tolerance of the emerald ash borer were investigated, and seasonal changes in these mechanisms monitored. The majority of emerald ash borers survive winter as freeze-intolerant prepupae. In winter, A. planipennis prepupae have low supercooling points (approximately -30°C), which they achieve by accumulating high concentrations of glycerol (approximately 4M) in their body fluids and by the synthesis of antifreeze agents. Cuticular waxes reduce inoculation from external ice. This is the first comprehensive study of seasonal changes in cold tolerance in a buprestid beetle.

The Siberian timberman Acanthocinus aedilis: a freeze-tolerant beetle with low supercooling points

Larvae of the Siberian timberman beetle Acanthocinus aedilis display a number of unique features, which may have important implications for the field of cold hardiness in general. Their supercooling points are scattered over a wide temperature range, and some individuals have supercooling points in the low range of other longhorn beetles. However, they differ from other longhorn beetles in being tolerant to freezing, and in the frozen state they tolerate cooling to below -37 degrees C. In this respect they also differ from the European timberman beetles, which have moderate supercooling capacity and die if they freeze. The combination of freezing tolerance and low supercooling points is unusual and shows that freezing at a high subzero temperature is not an absolute requirement for freezing tolerance. Like other longhorn beetles, but in contrast to other freeze-tolerant insects, the larvae of the Siberian timberman have a low cuticular water permeability and can thus stay supercooled for long periods without a great water loss. This suggests that a major function of the extracellular ice nucleators of some freeze-tolerant insects may be to prevent intolerable water loss in insects with high cuticular water permeability, rather than to create a protective extracellular freezing as has generally been assumed. The freezing tolerance of the Siberian timberman larvae is likely to be an adaptation to the extreme winter cold of Siberia.

Effects of polyhydroxy compounds on beetle antifreeze protein activity

Antifreeze proteins (AFPs) noncolligatively depress the nonequilibrium freezing point of a solution and produce a difference between the melting and freezing points termed thermal hysteresis (TH). Some low-molecular-mass solutes can affect the TH values. The TH enhancement effects of selected polyhydroxy compounds including polyols and carbohydrates on an AFP from the beetle Dendroides canadensis were systematically investigated using differential scanning calorimetry (DSC). The number of hydroxyl groups dominates the molar enhancement effectiveness of polyhydroxy compounds having one to five hydroxyl groups. However, the above rule does not apply for polyhydroxy compounds having more than five hydroxyl groups. The most efficient polyhydroxy enhancer identified is trehalose. In a combination of enhancers the strongest enhancer plays the major role in determining the TH enhancement. Mechanistic insights into identification of highly efficient AFP enhancers are discussed.

Cold hardiness of Apteropanorpa tasmanica Carpenter (Mecoptera: Apteropanorpidae)

There are very few investigations of cold hardiness in native Australian insects, and no such studies on insects from Tasmania. The Apteropanorpidae is a family of wingless Mecoptera endemic to Tasmania, comprising four described species that can be active in winter. In this study, we used infrared video thermography to investigate the physiological and behavioural responses of Apteropanorpa tasmanica to fast (0.3 degrees Cmin(-1)) and slow (0.03 degrees Cmin(-1)) rates of temperature reduction down to -10 degrees C. No adults survived cooling to -10 degrees C at either cooling rate. Mean supercooling points (SCPs) from fast cooling were -7.0 and -4.6 degrees C in 2002 and 2003, respectively. Ice nucleation always began in the abdomen, however, the position of nucleation within the abdomen varied between individuals. There was no relationship between SCP and body length, and no significant difference in SCPs between males and females. Stress-induced fast walking began when insects reached approximately -1.5 degrees C. Cooling rate did not affect the SCP or the temperature at which the behavioural stress response began. Adults survived for only short periods of time in the supercooled state; however they survived in the laboratory for up to 60 days at 4 degrees C, indicating their longevity at more favourable temperatures. Members of the Apteropanorpidae are adapted to the relatively warm, maritime climate currently influencing Tasmania.

Is the strategy for cold hardiness in insects determined by their water balance? A study on two closely related families of beetles: Cerambycidae and Chrysomelidae

The strategy for cold-hardiness and water balance features of two closely related families of Coleoptera, Cerambycidae and Chrysomelidae, were investigated. Cerambycids were freeze-avoiding with low supercooling points, whereas chrysomelids froze at high temperatures and were tolerant to freezing. Hence, the two families have adopted different strategies for cold-hardiness. Due to their low trans-cuticular water permeability, the cerambycids have low rates of evaporative water loss. Chrysomelids have much higher trans-cuticular water permeability, but freezing brings their body fluids in vapour pressure equilibrium with ice and prevents evaporative water loss. The differences in cold-hardiness strategies and rates of water loss are likely to reflect the water content of the diets of the two families. Cerambycids feed on dry wood with low water content, causing a restrictive water balance. Chrysomelids feed on leaves with high water content and may use evaporation through the cuticle as a route of water excretion. Haemolymph ice nucleators help chrysomelids to freeze at a high temperature and thus to maximize the period they spend in the water saving frozen state. The diet-related differences in water balance may be the reason why the two families have developed different strategies for cold-hardiness.

Inorganic ions in cold-hardiness

Cold exposure and freezing may affect ion distribution in several ways and reduce physiologically important ionic gradients. Both freeze-avoiding and freeze-tolerant organisms have developed mechanisms to handle this stress. Supercooled insects seem to be able to maintain their ionic gradients even at temperatures far below zero. When freeze-tolerant insects freeze, ions diffuse down their concentration gradients across the cell membranes and reach electrochemical equilibrium. They quickly reverse this transmembrane diffusion when they are thawed. Trace metals may affect mechanisms for cold-hardening in different ways and reduce cold-hardiness. Freezing may give rise to toxic concentrations of metal ions, and freeze-tolerant organisms probably need to inactivate toxic trace metals. Ice nucleating agents may be important in this context.

Ice nucleation in solutions and freeze-avoiding insects—homogeneous or heterogeneous?

This article challenges the common view that solutions and cold-hardy freeze-avoiding insects always freeze by heterogeneous nucleation. Data are presented to show that the nucleation temperatures of a variety of solutions and freeze-avoiding insects are a function of the water volume as described by the data previously published by Bigg in 1953. The article also points out that the relationships between melting point depression and depression of nucleation temperature are different for samples undergoing homogeneous nucleation and those undergoing heterogeneous nucleation. Aqueous solutions and freeze-avoiding insects display a relationship like that of homogeneously nucleated samples. It is also argued that the identity of the "impurities" assumed to cause heterogeneous nucleation in aqueous solutions and insects is obscure and that the "impurities" have features which make their existence rather unlikely.

Cold shock injury and ecological costs of rapid cold hardening in the grain aphid Sitobion avenae (Hemiptera: Aphididae)

The ability of first instar nymphs and newly moulted pre-reproductive adults of the grain aphid S. avenae to rapidly cold harden was investigated. When nymphs reared at 20 degrees C were transferred directly to -8 degrees C for 3 h, there was 18% survival. This exposure was selected as the discriminating temperature. Maximum increases in survival were achieved by acclimating nymphs for 2 h at 0 degrees C and adults for 3 h at 0 degrees C, resulting in survival of 83% and 68%, respectively. Cooling nymphs from 10 to 0 degrees C at different rates (1, 0.1 and 0.05 degrees C min(-1)) also increased cold hardiness, with the slowest rate of 0.05 degrees C min(-1) conferring the highest survival following exposure to the discriminating temperature. Adult aphids also expressed a rapid cold hardening response but to a lesser extent, with survival increasing from 16% to 68% following 3 h at 0 degrees C. There were no 'ecological costs' associated with rapid cold hardening in terms of development, longevity or fecundity. The data support the hypothesis that rapid cold hardening can be induced during the cooling phase of natural diurnal temperature cycles, allowing insects to track daily changes in environmental temperatures.

Physiological and ecological significance of biological ice nucleators

When a pure water sample is cooled it can remain in the liquid state at temperatures well below its melting point (0 degrees C). The initiation of the transition from the liquid state to ice is called nucleation. Substances that facilitate this transition so that it takes place at a relatively high sub-zero temperature are called ice nucleators. Many living organisms produce ice nucleators. In some cases, plausible reasons for their production have been suggested. In bacteria, they could induce frost damage to their hosts, giving the bacteria access to nutrients. In freeze-tolerant animals, it has been suggested that ice nucleators help to control the ice formation so that it is tolerable to the animal. Such ice nucleators can be called adaptive ice nucleators. There are, however, also examples of ice nucleators in living organisms where the adaptive value is difficult to understand. These ice nucleators might be structures with functions other than facilitating ice formation. These structures might be called incidental ice nucleators.

Effect of ice fraction and dilution factor on the antifreeze activity in the hemolymph of the cerambycid beetle Rhagium inquisitor

The freezing-melting hysteresis in a given volume of hemolymph from the cerambycid beetle Rhagium inquisitor was linearly and negatively related to the logarithm of the mass fraction of ice in the sample. When the ice fraction dropped by a factor of 10, the hysteresis activity increased by about 2 degrees C. When the hemolymph was diluted, the hysteresis activity was linearly and negatively related to the logarithm of the dilution factor. Dilution of the hemolymph by a factor of 2 led to a 1 degree C reduction in hysteresis activity. In the diluted samples, the ice growth took place along the a-axes, implying that the antifreeze peptides of insects block ice growth along the c-axis, in addition to the a-axis.

Ice nucleation and antinucleation in nature

Plants and ectothermic animals use a variety of substances and mechanisms to survive exposure to subfreezing temperatures. Proteinaceous ice nucleators trigger freezing at high subzero temperatures, either to provide cold protection from released heat of fusion or to establish a protective extracellular freezing in freeze-tolerant species. Freeze-avoiding species increase their supercooling potential by removing ice nucleators and accumulating polyols. Terrestrial invertebrates and polar marine fish stabilize their supercooled state by means of noncolligatively acting antifreeze proteins. Some organisms also depress their body fluid melting point to ambient temperature by evaporation and/or solute accumulation.

Cold hardiness adaptations of codling moth, cydia pomonella

The cold hardiness adaptations of natural and laboratory reared populations of the codling moth, Cydia pomonella, were examined. Hemolymph, gut, and whole body supercooling points (SCPs), 24-h LT50s, polyhydroxy alcohol concentrations, hemolymph freezing points, and hemolymph melting points were determined. Nondiapausing codling moth larvae do not have appreciable levels of ice nucleators in the hemolymph or gut. Whole body supercooling points were higher than hemolymph supercooling points. For nondiapausing larvae, LT50s were significantly higher than both the whole body and the hemolymph supercooling points, indicating the presence of chill sensitivity. As the larvae left the food source and spun a cocoon, both hemolymph and whole body SCPs decreased. Diapause destined larvae had significantly lower hemolymph SCPs than nondiapausing larvae, but whole body SCPs were not significantly different from nondiapausing larvae of the same age. The LT50s of diapause destined and diapausing larvae were significantly lower than that of nondiapausing larvae. Codling moths are freezing intolerant, with LT50s close to the average whole body supercooling point in diapause destined and diapausing larvae. The overwintering, diapausing larvae effectively supercool to avoid lethal freezing by removal of ice nucleators from the gut and body without appreciable increase of antifreeze agents such as polyols or antifreeze proteins.

Factors affecting the freeze tolerance of the hoverfly Syrphus ribesii (Diptera: syrphidae)

Larvae of Syrphus ribesii collected from overwintering sites in the U.K. are strongly freeze tolerant with 70% survival at -35 degrees C. The cold tolerance of laboratory reared insects increased with increasing periods of acclimation at 0 degrees C, with a concurrent rise in the supercooling point (SCP) from -6.8+/-0.1 to -5.1+/-0.3 degrees C. There was 50% survival in the most cold-hardy group 72h after brief exposures to -30 degrees C. The retention of gut contents caused a decrease in cold hardiness, with only 13% of larvae surviving 72h after exposure to -15 degrees C, with no subsequent pupation or emergence. Wet larvae had a significantly higher SCP (-5.0+/-0.2 degrees C) compared to dry larvae (-7.8+/-0.4 degrees C), although survival of larvae was similar in both groups. There was no nucleator activity in the haemolymph of field collected larvae. The importance of these findings are discussed in relation to the freeze tolerance strategy of S. ribesii.

Cryopreservation of mammalian embryos and oocytes: Recent advances

The cryopreservation of embryos of most domestic species has become a routine procedure in embryo transfer, and recently, advances have been made in the cold storage of mammalian oocytes. The ability to sustain viable oocytes and embryos from mammalian species at low temperature for prolonged periods of time has important implications to basic and applied biotechnology. Recent advances in the study of physico-chemical behaviour of different cryoprotectants, use of various macromolecule additives in cryoprotective solutions and isolation and use of proteins of plant and animal origin with antifreeze activity offers many new options for cryopreservation of oocytes and embryos of animal and human origin. At the same time rapidly developing methods of oocyte/embryo manipulation such as in vitro embryo production, embryo splitting, embryo biopsying for gene and sex determination, embryo cloning and the isolation of individual blastomers, create new challenges in cryopreservation. Very recent advances in the cryopreservation of mammalian oocytes, in vivo- and in vitro-derived embryos, and micromanipulated embryos are reviewed in this manuscript.

Ice nucleating activity in the blood of the freeze-tolerant frog, Rana sylvatica

Although the presence of antifreeze and ice nucleating agents in the hemolymph of insects has been well documented, there have been no reports of either of these types of agent in vertebrates. The technique of differential scanning calorimetry was used to examine the blood, serum, and plasma of a freeze-tolerant frog, Rana sylvatica, for the presence of antifreeze protein activity. Results demonstrate the absence of antifreeze protein but the presence of an ice nucleating agent that may serve as a functional component of the overwintering strategy of this species. Ice nucleating activity was detected in samples of cell-free blood, serum, and plasma, suggesting that the agent is a soluble component and possibly plasma protein. To our knowledge, the identification of ice nucleating activity in this freeze-tolerant vertebrate is novel.

Freeze tolerance and intolerance as strategies of winter survival in terrestrially-hibernating amphibians

The ability to tolerate extracellular freezing as an adaptation for winter survival was tested in seven species of terrestrially-hibernating amphibians found in eastern Canada. All species had only moderate supercooling abilities, with whole animal supercooling points of -1.5 to -3 degrees C. Two salamander species, Plethodon cinereus and Ambystoma laterale, and the toad, Bufo americanus, were freezing intolerant and were killed when frozen for 24 hr at temperatures just below their supercooling points. The major winter strategy of these animals appears to behavioural avoidance of subzero temperatures. Four species of frogs Rana sylvatica, Hyla versicolor, Hyla crucifer and Pseudacris triseriata, survived extracellular freezing at moderate subzero temperatures (-2 to -4 degrees C) for periods of time ranging up to 2 weeks. All four frog species accumulated low molecular weight carbohydrates as cryoprotectants, glycerol being the major cryoprotectant in adult H. versicolor, while immature adults of this species as well as the other three species all produced high levels of glucose as the cryoprotectant.

Metabolism and bound water in overwintering insects

The freezing-tolerant gall fly larva, Eurosta solidaginis, provides an excellent model system for the study of metabolic adaptation and metabolic control for low-temperature survival during overwintering. Low-temperature acclimation of the larvae results in dramatic alterations in metabolic flux producing a sequential synthesis of two cryoprotectants, glycerol at warmer temperatures followed by sorbitol when larvae are exposed to 5 degrees C. Regulation of metabolism in the larvae appears to exploit temperature change, temperature effects on enzyme kinetics, and temperature/modulator interactions with enzymes producing the alterations in metabolic flux leading to differential polyol synthesis. For instance, temperature/modulator effects on phospho-fructokinase appear to be the major factor halting carbon flow into glycerol synthesis at low temperatures and diverting flux instead into the pathway of sorbitol synthesis. Alterations in the cellular content of bound water and the metabolic pools of free versus bound soluble metabolites may also have important regulatory consequences for low-temperature metabolism. Bound water content of the larvae increases with low-temperature acclimation and is attributable to changes in water binding by both low-molecular-weight (polyols) and high-molecular-weight (proteins, glycogen) subcellular components. A restrictive effect of high bound water content may be one factor causing the strong depression of metabolic activity seen in the larvae as a result of extracellular freezing. In addition, bound water may have a more subtle effect in determining the relative pool sizes of bound versus free metabolites in the cell. 31P-NMR studies of whole larvae show that the content of free phosphorylated intermediates in the cell diminishes with decreasing temperatures despite a measured constancy in the total pool size of these intermediates. An increase in the content of bound metabolites with low temperature may restrict metabolism by limiting the availability of substrates and effectors of enzyme reactions.

Properties of sodium and potassium channels of the squid giant axon far below 0 degrees C

Squid giant axon could be excited in concentrated glycerol solutions containing normal concentrations of electrolytes, when osmolalities of solutions inside and outside the axon were matched. These glycerol solutions did not freeze at the temperature as low as -19 degrees C. The nerve excitation in these solutions were observed at this low temperature. The excitation process at this low temperature was slowed down and time constants of the excitation kinetics were several hundredfold larger than those in normal seawater at 10 degrees C, under which temperature the squid habituated. The temperature coefficients for the electrophysiological membrane parameters under this condition were larger than those in normal seawater above 0 degrees C. The Q10 value for the conduction velocity was 2.0 and that of the duration of the action potential was around 8.5. The time course of the membrane currents was also slowed with the Q10 value of around 5 and the magnitude decreased with the Q10 value of around 2 as the temperature was lowered. The Q10 values for the kinetics of the on process of the Na-channel were around 4.5 and were almost the same as those of the off process of the Na-channel in the wide range of the temperature below 0 degrees C. The Q10 value of the on process of K-channel was around 6.5 and was larger than those for Na-channel. The Q10 values increased gradually as the temperature was lowered.