COLD TOLERANCE OF MICROARTHROPODS

1. Microarthropods (Acari and Collembola) are dominant components of the terrestrial fauna in the Antarctic. Their cold tolerance, which forms the mainspring of their adaptational strategy, is reviewed against a background of their structure and function, and by comparison with other arthropods. 2. Two species, the isotomid collembolan Cryptopygus antarcticus Willem and the oribatid mite Alaskozetes antarcticus (Michael), are examined in detail, and afford a comparative approach to the mechanisms underlying cold tolerance in insect and arachnid types. 3. All microarthropods appear to be freezing-susceptible (unable to tolerate tissue ice), and they utilize varying levels of supercooling to avoid freezing. Gut contents are considered to be the prime nucleation site in most arthropods when supercooled, particularly for Antarctic species. Moulting also increases individual supercooling ability especially in Collembola, and the activity of ice-nucleating bacteria in cold-hardy arthropods may be important. 4. Sources of ice nucleators are many and varied, originating externally (motes) or internally (ice-nucleating agents). They act either extracellularly (mainly in the haemolymph) to promote freezing in ice-tolerant life stages, or intracellularly in freezing-susceptible forms. Thermal hysteresis proteins, acting colligatively, occur in many arthropods including Collembola; they depress both the freezing point of body fluids and the whole-body supercooling point of freezing- susceptible and freezing-tolerant species. 5. Bimodal supercooling point distributions are a feature of microarthropods and water droplets. Samples of field populations of Antarctic mites and springtails show significant seasonal changes in these distributions, which in some respects are analogous to purely physical systems of water droplets. Supercooling points are confirmed as accurate measures of cold-hardiness and survival for Antarctic species, but not necessarily for other arthropods. The effects of constant sub-zero temperatures approaching the limit of the supercooling ability of arthropods require study. 6. Desiccation and dehydration influence microarthropod physiology in several ways; in Alaskozetes it triggers glycerol synthesis. Glycerol may aid binding of water in severely dehydrated insects, but the relationship of such ‘bound’ water to cold-hardiness is unclear. 7. Sugar alcohols (polyols) and sugars are accumulated as potential cryoprotectants in many arthropods at low temperatures, and antifreeze systems may be single or multi-component in structure. Cryoprotectant synthesis and regulation have been studied principally in insects, and fresh weight concentrations of 0–3-5 M of polyols have been found. Trehalose accumulation may also influence cold-hardiness. 8. Microarthropods fall within the spectrum of cold tolerance observed for arthropods and other invertebrates. No special adaptations are found in Antarctic species, and similar strategies and mechanisms are present in both insects and arachnids. The colonization and maintenance of microarthropod populations of polar land habitats seem not to have required the evolution of any novel features with respect to cold tolerance.     

The supercooling ability of ticks (Acari,Ixodoidea)

 The supercooling capacity of nine laboratory- held species of ticks originating from different geographical areas, as well as five field-collected species from Germany, was investigated. All but one tick species showed mean supercooling points between about −17 and −23 °C, suggesting that the capacity to supercool to temperatures of ≤−17 °C might be an inherent property of many tick species unrelated to their geographic origin. Photoperiod did not influence the mean supercooling point in any of the species and there was also no distinct seasonal pattern of supercooling in seasonally acclimatized Dermacentor marginatus. Thus, the supercooling ability was independent of the presence/absence of diapause. The finding of thermal hysteresis in D. marginatus hemolymph raises the question of whether or not anti-freeze proteins are involved in the supercooling capacity of that species. An interspecies comparison revealed a weak negative correlation between relative water content and supercooling point of the ticks and an even weaker correlation between body mass or body water mass and the supercooling point. Since the ticks exhibited low supercooling points both before and shortly after feeding, the blood used as food should lack potent ice nucleators. Accepted: 14 June 1996     

Freezing avoidance of the Antarctic icefishes (Channichthyidae) across thermal gradients in the Southern Ocean

Biogeographic studies separate the Antarctic Notothenioid fish fauna into high- and low-latitude species. Past studies indicate that some species found in the high-latitude freezing waters of the High-Antarctic Zone have low-serum hysteresis freezing points, while other species restricted to the low-latitude seasonal pack ice zone have higher serum hysteresis freezing points above the freezing point of seawater (−1.9°C), but the relationship has not been systematically investigated. Freeze avoidance was quantified in 11 species of Antarctic icefishes by determining the hysteresis freezing points of their blood serum, in addition, the freezing point depression from serum osmolytes, the antifreeze activity from serum antifreeze glycoproteins (AFGPs), and the antifreeze activity from serum antifreeze potentiating protein were measured for each species. Serum hysteresis freezing point, a proxy for organismal freeze avoidance, decreased as species were distributed at increasing latitude (linear regression r ² 0.66, slope −0.046°C °latitude⁻¹), which appeared largely independent of phylogenetic influences. Greater freeze avoidance at high latitudes was largely a result of higher levels of antifreeze activity from serum AFGPs relative to those in species inhabiting the low-latitude waters. The icefish fauna could be separated into a circum High-Antarctic Group of eight species that maintained serum hysteresis freezing points below −1.9°C even when sampled from less severe habitats. The remaining three species with low-latitude ranges restricted to the waters of the northern part of the west Antarctic Peninsula and Scotia Arc Islands had serum hysteresis freezing points at or above −1.9°C due to significantly lower combined activity from all of their serum antifreeze proteins than found in the High-Antarctic Zone icefish.     

Subzero temperature tolerance in spiders: The role of thermal-hysteresis-factors

Summary The immature stages of two species of spiders which overwinter under the bark of standing dead trees survive subzero temperatures by depressing their supercooling points in winter. These are a crab spider,Philodromus sp. (Philodromidae), and a sac spider,Clubiona sp. (Clubionidae). The solutes which are at least partially responsible for the decrease in supercooling points in winter are: (1) proteins which produce a thermal hysteresis (a difference between the freezing and melting points) of approximately 2°C in the hemolymph and (2) glycerol. The thermal-hysteresis-factors and glycerol are only found in the spiders in winter. Acclimation of winter spiders to warm temperatures, at either long or short photoperiods, results in loss of the thermal hysteresis within two weeks. These thermal-hysteresis-factors appear to be similar to protein and glycoprotein antifreezes previously found in polar marine fishes and certain overwintering insects.     

Insect antifreezes and ice-nucleating agents

Cold-tolerant, freeze-susceptible insects (those which die if frozen) survive subzero temperatures by proliferating antifreeze solutes which lower the freezing and supercooling points of their body fluids. These antifreezes are of two basic types. Lowmolecular-weight polyhydroxy alcohols and sugars depress the freezing point of water on a colligative basis, although at higher concentrations these solutes may deviate from linearity. Recent studies have shown that these solutes lower the supercooling point of aqueous solutions approximately two times more than they depress the freezing point. Consequently, if a freeze-susceptible insect accumulates sufficient glycerol to lower the freezing point by 5 °C, then the glycerol should depress the insect's supercooling point by 10 °C.Some cold-tolerant, freeze-susceptible insects produce proteins which produce a thermal hysteresis (a difference between the freezing and melting point) of several degrees in the body fluids. These thermal hysteresis proteins (THPs) are similar to the antifreeze proteins and glycoproteins of polar marine teleost fishes. The THPs lower the freezing, and presumably the supercooling, point by a noncolligative mechanism. Consequently, the insect can build up these antifreezes, and thereby gain protection from freezing, without the disruptive increases in osmotic pressure which accompany the accumulation of polyols or sugars. Therefore the THPs can be more easily accumulated and maintained during warm periods in anticipation of subzero temperatures. It is not surprising then that photoperiod, as well as temperature, is a critical environmental cue in the control of THP levels in insects.Some species of freeze-tolerant insects also produce THPs. This appears somewhat odd, since most freeze-tolerant insects produce ice nucleators which function to inhibit supercooling and it is therefore not clear why such an insect would produce antifreeze proteins. It is possible that the THPs have an alternate function in these species. However, it also appears that the THPs function as antifreezes during those periods of the year when these insects are not freeze tolerant (i.e., early autumn and spring) but when subzero temperatures could occur. In addition, at least one freeze-tolerant insect which produces THPs, Dendroides canadensis, typically loses freeze tolerance during midwinter thaws and then regains tolerance. The THPs could be important during those periods when Dendroides loses freeze tolerance by making the insect less susceptible to sudden temperature decreases.Comparatively little is known of the biochemistry of insect THPs. However, comparisons of those few insect THPs which have been purified with the THPs of fishes show some interesting differences. The insect THPs lack the large alanine component commonly found in the fish THPs. In addition, the insect THPs generally contain greater percentages of hydrophilic amino acids than do those of the fish. Perhaps the most interesting insect THPs are those from Tenebrio molitor which have an extremely large cysteine component (28% in one THP). Studies on the primary and higher-order structure of the insect THPs need to be carried out so that more critical comparisons with the fish THPs can be made. This may provide important insights into the mechanisms of freezing point and supercooling point depression exhibited by these molecules. In addition, comparative studies of the freezing and supercooling point depressing activities of the various THPs, in relation to their structures, should prove most interesting.It has become increasingly apparent over the last few years that most freeze-tolerant insects, unlike freeze-susceptible species, inhibit supercooling by accumulating ice-nucleating agents in their hemolymph. These nucleators function to ensure that ice formation occurs in the extracellular fluid at fairly high temperatures, thereby minimizing the possibility of formation of lethal intracellular ice. Little is known of the nature of the insect ice-nucleating agents. Those few which have been studied are heat sensitive and nondialyzable and are inactivated by proteolytic enzymes, thus indicating that they are proteinaceous. Studies on the structure-function relationships of these unique molecules should be done.     

The effect of feeding on specific soil algae on the cold-hardiness of two Antarctic micro-arthropods (Alaskozetes antarcticus and Cryptopygus antarcticus)

The effect of consuming terrestrial algae on the cold tolerance of two Antarctic micro-arthropods was examined. From the results of preferential feeding experiments, seven species of Antarctic terrestrial micro-algae were chosen and fed to two common, freeze-avoiding Antarctic micro-arthropods: the springtail Cryptopygus antarcticus (Collembola: Isotomidae), and the mite Alaskozetes antarcticus (Acari: Oribatida). Mites were very selective in their choice of food whereas the springtails were less discriminating. The ice nucleating activity of each species of alga was measured using an ice nucleator spectrometer and a differential scanning calorimeter. Pure cultures of individual species of algae had characteristic supercooling points ranging from ca. −5 to −18 °C. The effect of eating a particular alga on the supercooling point of individual micro-arthropods cultured at two different temperatures (0 and 10 °C) was examined. Neither species showed a preference for algae with low ice-nucleating activity and there was no clear correlation between the supercooling point of food material and that of the whole animal. However, feeding on certain algae such as Prasiola crispa, which contained the most active ice nucleators, decreased the cold tolerance of both species of arthropods. Accepted: 6 May 2000     

Stabilization of supercooled fluids by thermal hysteresis proteins.

It has been reported that thermal hysteresis proteins found in many cold-hardy, freeze-avoiding arthropods stabilize their supercooled body fluids. We give evidence that fish antifreeze proteins, which also produce thermal hysteresis, bind to and reduce the efficiency of heterogenous nucleation sites, rather than binding to embryonic ice nuclei. We discuss both possible mechanisms for stabilization of supercooled body fluids and also describe a new method for measuring and defining the supercooling point of small volumes of liquid.     

Ecological contrasts across an Antarctic land–sea interface

Abstract We report the composition of terrestrial, intertidal and shallow sublittoral faunal communities at sites around Rothera Research Station, Adelaide Island, Antarctic Peninsula. We examined primary hypotheses that the marine environment will have considerably higher species richness, biomass and abundance than the terrestrial, and that both will be greater than that found in the intertidal. We also compared ages and sizes of individuals of selected marine taxa between intertidal and subtidal zones to test the hypothesis that animals in a more stressed environment (intertidal) would be smaller and shorter lived. Species richness of intertidal and subtidal communities was found to be similar, with considerable overlap in composition. However, terrestrial communities showed no overlap with the intertidal, differing from previous reports, particularly from further north on the Antarctic Peninsula and Scotia Arc. Faunal biomass was variable but highest in the sublittoral. While terrestrial communities were depauperate with low biomass they displayed the highest overall abundance, with a mean of over 3 × 10⁵ individuals per square metre. No significant differences in ages of intertidal and subtidal individuals of the same species were found, with bryozoan colonies of up to 4 years of age being present in the intertidal. In contrast with expectation and the limited existing literature we conclude that, while the Antarctic intertidal zone is clearly a suboptimal and highly stressful habitat, its faunal community can be well established and relatively diverse, and is not limited to short‐term opportunists or waifs and strays.     

Comparative analysis of overwintering physiology in nine species of semi‐aquatic bugs (Heteroptera: Gerromorpha)

In semi‐aquatic bugs (Heteroptera: Gerromorpha), the strategies of overwintering in a cryothermic state (i.e. at body temperatures below the equilibrium freezing point) remain largely unexplored. The present study provides an analysis of the ecophysiological aspects of overwintering in nine gerromorphan species. All nine species avoid ice formation by means of a more or less extensive supercooling of their body fluids. There is a tight correlation between the supercooling point (SCP) and the lower lethal temperature. Different species use different physiological adjustments to increase the likelihood of survival in a supercooled state. These include stabilization of the supercooled state by active antifreeze factors that cause thermal hysteresis between equilibrium melting and freezing points, the accumulation of low‐molecular weight sugars and polyols with putative cryoprotective functions, or by having a relatively high body fluid osmolality, combined with a low level of hydration. The majority of species under study overwinter only as adults, whereas Velia caprai Tamanini can overwinter either as an adult or in the egg stage. The supercooling capacity of V. caprai adults is insufficient to prevent the risk of lethal freezing. The adults therefore survive only opportunistically in suitable microhabitats, and/or during mild winters. The survival of V. caprai in winter is assured by extensive supercooling and having overwintering eggs that are highly cold tolerant.     

The inhibition of ice nucleators by insect antifreeze proteins is enhanced by glycerol and citrate

Antifreeze proteins depress the freezing point of water while not affecting the melting point, producing a characteristic difference in freezing and melting points termed thermal hysteresis. Larvae of the beetle Dendroides canadensis accumulate potent antifreeze proteins (DAFPs) in their hemolymph and gut, but to achieve high levels of thermal hysteresis requires enhancers, such as glycerol. DAFPs have previously been shown to inhibit the activity of bacterial and hemolymph protein ice nucleators, however, the effect was not large and therefore the effectiveness of the DAFPs in promoting supercooling of the larvae in winter was doubtful. However, this study demonstrates that DAFPs, in combination with the thermal hysteresis enhancers glycerol (1 M) or citrate (0.5 M), eliminated the activity of hemolymph protein ice nucleators and Pseudomonas syringae ice-nucleating active bacteria, and lowered the supercooling points (nucleation temperatures) of aqueous solutions containing these ice nucleators to those of water or buffer alone. This shows that the DAFPs, along with glycerol, play a critical role in promoting hemolymph supercooling in overwintering D. canadensis. Also, DAFPs in combination with enhancers may be useful in applications which require inhibition of ice nucleators.     

Experimental studies on the cold tolerance of Alaskozetes antarcticus

The cold tolerance mechanism of the Antarctic terrestrial mite Alaskozetes antarcticus (Michael) was investigated in cultured animals. Freezing is fatal in this species and winter survival occurs by means of supercooling, which is enhanced by the presence of glycerol in the body. There is an inverse, linear relationship between the concentration of glycerol and the supercooling point, which may be as low as ?30°C. Feeding detracts from supercooling ability by providing ice nucleators in the gut which initiate freezing at relatively high sub-zero temperatures. Experiments on the effects of various environmental factors showed that low temperature acclimation gave rise to increased glycerol concentrations and suppressed feeding, while desiccation also stimulated glycerol production. Photoperiod had no effect on cold tolerance in this species. The juvenile instars of A. antarcticus were found to possess a greater degree of low temperature tolerance than adults.     

Distribution and temperature tolerance of the Antarctic free-living mite Antarcticola meyeri (Acari,Cryptostigmata)

The ecology and physiology of a free-living mite species Antarcticola meyeri, Cryptostigmata, rarely discovered in the Continental Antarctic Zone, were studied near the Japanese Antarctic Base, Syowa Station. The distribution of this mite species correlated noticeably with the distribution of its food, the imperfect lichen species, which grow in moss carpets. Within a limited habitat, this mite species preferred dry carpets to wet carpets. Low humidity appeared disadvantageous to the species at high temperatures (ca. 30°C), but at low temperatures (ca. -25°C), low humidity appeared advantageous. This may explain why this species preferred dry carpets. The mean supercooling point of starved individuals was -30.6°C (nymphs) to-33.9°C (eggs). When fed with lichens, however, it was significantly raised, probably because the gut contents functioned as ice nucleators or contained ice-nucleating agents. Acclimation to low temperatures significantly lowered the supercooling point of larvae but not of other growth stages.     

Differential thermal tolerance and energetic trajectories during ontogeny in porcelain crabs,genus Petrolisthes

Thermal tolerance limits of marine intertidal zone organisms are elevated compared to subtidal species, but are typically just slightly higher than maximal habitat temperatures. The small thermal safety margins maintained by intertidal zone organisms suggest that high thermal tolerance is associated with a physiological cost. If true, we hypothesize that species that transition between intertidal zone and planktonic habitats during ontogeny, will adjust their thermal tolerance accordingly to capitalize upon potential energy savings while in a thermally benign habitat. We tested this hypothesis in porcelain crabs that transition between the thermally stressful, intertidal zone as embryos, to the thermally benign pelagic zone as larvae, and back at settlement. We found the more thermally tolerant, mid-intertidal zone species, Petrolisthes cinctipes, and the less thermally tolerant, subtidal zone species, Petrolisthes manimacilis, exhibited reduced thermal tolerance (LT₅₀) in the transition from embryos to larvae. This was associated with an increased oxygen consumption rate in both species, though P. cinctipes exhibited a significantly greater increase in oxygen consumption. P. cinctipes also showed an increase in thermal tolerance in settled juveniles compared to pelagic zoea I larvae, resulting in an overall V-shaped thermal tolerance relationship during ontogeny, while in P. manimaculis thermal tolerance was significantly lower in juveniles compared to zoea I. In neither species were these changes (zoea I to juvenile) associated with a significant change in metabolism. While embryos and juveniles of P. cinctipes have thermal tolerance limits near intertidal habitat thermal maxima (∼32.5 °C), all three life-history stages in P. manimaculis (especially embryos and larvae) exhibit considerable thermal safety margins. The mechanisms underlying this “excess” thermal tolerance in P. manimacilis embryos are unknown, but suggest that patterns of thermal tolerance in early life history stages are species-specific.     

Strategies of cold-hardiness in three species of Antarctic dorylaimid nematodes

Summary Three species of free-living Antarctic fellfield nematodes, Eudorylaimus coniceps, E. spaulli and E. pseudocarteri exhibited differing degrees of both strategies of cold-hardiness; freeze-tolerance and freeze-avoidance. Bimodal distributions of supercooling points were obtained from monthly field samples of both E. coniceps and E. spaulli. Individuals found in the low group of this distribution (supercooling to <-15 °C) were capable of avoiding freezing by extensive supercoolint (to a mean temperature of ca-22 °C), sufficient to with-stand the environmental extremes of the maritime Antarctic. The high groups of both these species, and almost all E. pseudocarteri, were likely to have frozen at some stage during winter. Survival of freezing increased with the temperature at which nucleation occurred, and has been described by a Gompertz model. Estimates of the supercooling points at which survival fell to 50% were-10.4,-7.1 and-6.1 °C for E. coniceps, E. pseudocarteri and E. spaulli, respectively.     

Cryoprotective mechanisms in subtidally cultivated and intertidal blue mussels (mytilus edulis) from the Magdalen Islands, Québec

Centrifuged extracts from subtidally cultivated and intertidal blue mussels have higher supercooling points (up to -5.5°C) in winter than in summer (up to -12.5°C). The concentration of nucleators (as estimated by the dilution factor) is greater in winter than in summer in both groups. The nucleator concentration in the extracts of winter mussels is one to two orders of magnitude higher than that in the haemolymph of Norwegian mussels. Although these extracts show spilule-like growth of ice crystals, they caused no thermal hystersis. The seasonal variation of these cryoprotective mechanisms is similar for intertidal and cultivated mussels. However, in the spring, cultivated mussels have a lower supercooling point and a lower concentration of nucleators than their intertidal counterparts. This suggests that cultivated mussels decrease their cryoprotective capacity earlier than intertidal mussels.     

Variability in intertidal communities along a latitudinal gradient in the Southern Ocean

Despite being one of the most intensely studied habitat types worldwide, the intertidal region around Antarctica has received little more than superficial study. Despite this, the first detailed study of a single locality on the Antarctic Peninsula reported previously unanticipated levels of species richness, biomass and diversity in cryptic intertidal habitats. The current study extends the coverage achieved from this single locality. The intertidal zone at sites in the Scotia Arc, the Falkland Islands and the Antarctic Peninsula was investigated. At all the study sites selected, a wide range of macrofauna was found inhabiting the littoral fringe. These communities, although generally cryptic and occupying predominantly the undersides of boulders and protected interstices, at some locations and sites were rich at multiple taxonomic levels. Across the study locations species richness in the intertidal zone ranged from 7 to 30 species. The highest species richness and diversity were found at high latitude localities, which experienced the highest physical disturbance due to ice scour, and appeared superficially to be denuded of life. Species assemblages varied with latitude with Adelaide Island having a high proportion of bryozoans relative to all other localities.     

Causes and consequences of thermal tolerance limits in rocky intertidal porcelain crabs, genus petrolisthes

Vertical zonation of intertidal organisms, from the shallowsubtidal to the supralittoral zones, is a ubiquitous featureof temperate and tropical rocky shores. Organisms that livehigher on the shore experience larger daily and seasonal fluctuationsin microhabitat conditions, due to their greater exposure toterrestrial conditions during emersion. Comparative analysesof the adaptive linkage between physiological tolerance limitsand vertical distribution are the most powerful when the studyspecies are closely related and occur in discrete vertical zonesthroughout the intertidal range. Here, I summarize work on thephysiological tolerance limits of rocky intertidal zone porcelaincrab species of the genus Petrolisthes to emersion-related heatstress. In the eastern Pacific, Petrolisthes species live throughouttemperate and tropical regions, and are found in discrete verticalintertidal zones in each region. Whole organism thermal tolerancelimits of Petrolisthes species, and thermal limits of heartand nerve function reflect microhabitat conditions. Speciesliving higher in the intertidal zone are more eurythermal thanlow-intertidal congeners, tropical species have the highestthermal limits, and the differences in thermal tolerance betweenlow- and high-intertidal species is greatest for temperate crabs.Acclimation of thermal limits of high-intertidal species isrestricted as compared to low-intertidal species. Thus, becausethermal limits of high-intertidal species are near current habitattemperature maxima, global warming could most strongly impactintertidal species.     

Thermal plasticity is independent of environmental history in an intertidal seaweed

Organisms inhabiting the intertidal zone have been used to study natural ecophysiological responses and adaptations to thermal stress because these organisms are routinely exposed to high‐temperature conditions for hours at a time. While intertidal organisms may be inherently better at withstanding temperature stress due to regular exposure and acclimation, they could be more vulnerable to temperature stress, already living near the edge of their thermal limits. Strong gradients in thermal stress across the intertidal zone present an opportunity to test whether thermal tolerance is a plastic or canalized trait in intertidal organisms. Here, we studied the intertidal pool‐dwelling calcified alga, Ellisolandia elongata, under near‐future temperature regimes, and the dependence of its thermal acclimatization response on environmental history. Two timescales of environmental history were tested during this experiment. The intertidal pool of origin was representative of long‐term environmental history over the alga's life (including settlement and development), while the pool it was transplanted into accounted for recent environmental history (acclimation over many months). Unexpectedly, neither long‐term nor short‐term environmental history, nor ambient conditions, affected photosynthetic rates in E. elongata. Individuals were plastic in their photosynthetic response to laboratory temperature treatments (mean 13.2°C, 15.7°C, and 17.7°C). Further, replicate ramets from the same individual were not always consistent in their photosynthetic performance from one experimental time point to another or between treatments and exhibited no clear trend in variability over experimental time. High variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level over time.     

Local distribution and thermal ecology of two intertidal fishes

Geographic variability in the physiological attributes of widely distributed species can be a result of phenotypic plasticity or can reflect evolutionary responses to a particular habitat. In the field, we assessed thermal variability in low and high intertidal pools and the distribution of resident fish species Scartichthys viridis and transitory Girella laevifrons along this vertical intertidal gradient at three localities along the Chilean coast: Antofagasta (the northernmost and warmest habitat), Carrizal Bajo (central coast) and Las Cruces (the southernmost and coldest habitat). In the laboratory, we evaluated the thermal sensitivity of fish captured from each locality. The response to temperature was estimated as the frequency of opercular movements and as thermal selectivity in a gradient; the former being a indirect indicator of energy costs in a particular environment and the latter revealing differential occupation of habitat. Seawater temperature in intertidal pools was greatest at Antofagasta, and within each site was greatest in high intertidal pools. The two intertidal fish species showed opposite patterns of local distribution, with S. viridis primarily inhabiting the lower sectors of the intertidal zone, and G. laevifrons occupying the higher sectors of the intertidal zone. This pattern was consistent for all three localities. Locality was found to be a very important factor determining the frequency of opercular movement and thermal selectivity of both S. viridis and G. laevifrons. Our results suggest that S. viridis and G. laevifrons respond according to: (1) the thermal history of the habitat from which they came, and (2) the immediate physical conditions of their habitat. These results suggest local adaptation rather than plasticity in thermoregulatory and energetic mechanisms.     

Winter survival of an adult bark beetle Ips acuminatus Gyll

Freezing-susceptible adult Ips acuminatus hibernate underneath bark of Scots pine. The beetles lower their supercooling points from ?20 to ?34°C due to accumulation of low molecular weight antifreezes. The capability of specimens to supercool to about ?20°C in the absence of cryoprotective solutes during winter, seemed to be at least partially attributable to the presence of a thermal hysteresis factor at 3–4°C.Using a GC-MS-COM technique, a unique combination of accumulated solutes present only in specimens demonstrating supercooling points below ?20°C was identified as ethylene glycol, mannitol, sorbitol and dulcitol. Not previously found in nature, ethylene glycol was the major solute (90%) synthesized at sub-zero temperatures. Exposure to ?10°C was an effective cue to accumulation of ethylene glycol and nearly 5 times as effective in promoting sorbitol synthesis than was ?5°C. When low molecular weight substances were lost at high temperatures, they were not re-synthesized in beetles re-exposed to sub-zero temperature. The supercooling point was closely related to both the concentration of ethylene glycol and to the haemolymph melting point. Attempts to correlate changes in sorbitol concentrations to changes in supercooling points were not conclusive.Proliferation of thermal hysteresis was observed in the beginning of November. A melting-hysteresis freezing point differential of about 3.6°C was demonstrated in the haemolymph of beetles during December. No thermal hysteresis was demonstrated in the haemolymph of positive phototactic beetles or in the outdoor beetles in May. The combination of high temperature and long photoperiod appeared to be a more effective cue to the final loss of thermal hysteresis than was high temperature alone.