Cold tolerance of Alpine, Arctic, and Antarctic Collembola and mites

Temporal regulation of temperature tolerances and gene expression in an arctic insect

Terrestrial arthropods in the Arctic are exposed to highly variable temperatures that frequently reach cold and warm extremes. Yet, ecophysiological studies on arctic insects typically focus on the ability of species to tolerate low temperatures, whereas studies investigating physiological adaptations of species to periodically warm and variable temperatures are few. In this study, we investigated temporal changes in thermal tolerances and the transcriptome in the Greenlandic seed bug Nysius groenlandicus, collected in the field across different times and temperatures in Southern Greenland. We found that plastic changes in heat and cold tolerances occurred rapidly (within hours) and at a daily scale in the field, and that these changes are correlated with diurnal temperature variation. Using RNA sequencing, we provide molecular underpinnings of the rapid adjustments in thermal tolerance across ambient field temperatures and in the laboratory. We show that transcriptional responses are sensitive to daily temperature changes, and days characterized by high temperature variation induced markedly different expression patterns than thermally stable days. Further, genes associated with laboratory-induced heat responses, including expression of heat shock proteins and vitellogenins, were shared across laboratory and field experiments, but induced at time points associated with lower temperatures in the field. Cold stress responses were not manifested at the transcriptomic level.

Ecology of the cold-adapted species Nebria germari (Coleoptera: Carabidae): the role of supraglacial stony debris as refugium during the current interglacial period

In the current scenario of climate change, cold-adapted insects are among the most threatened organisms in high-altitude habitats of the Alps. Upslope shifts and changes in phenology are two of the most investigated responses to climate change, but there is an increasing interest in evaluating the presence of high-altitude landforms acting as refugia. Nebria germari Heer, 1837 (Coleoptera: Carabidae) is a hygrophilic and cold-adapted species that still exhibits large populations on supraglacial debris of the Eastern Alps. This work aims at describing the ecology and phenology of the populations living on supraglacial debris. To this end, we analysed the populations from three Dolomitic glaciers whose surfaces are partially covered by stony debris. We found that supraglacial debris is characterised by more stable colder and wetter conditions than the surrounding debris slopes and by a shorter snow-free period. The populations found on supraglacial debris were spring breeders, differently from those documented in the 1980s on Dolomitic high alpine grasslands, which were reported as autumn breeders. Currently, Nebria germari seems, therefore, to find a suitable habitat on supraglacial debris, where micrometeorological conditions are appropriate for its life-cycle and competition and predation are reduced.

Surviving in a frozen desert: environmental stress physiology of terrestrial Antarctic arthropods

Abiotic stress is one of the primary constraints limiting the range and success of arthropods, and nowhere is this more apparent than Antarctica. Antarctic arthropods have evolved a suite of adaptations to cope with extremes in temperature and water availability. Here, we review the current state of knowledge regarding the environmental physiology of terrestrial arthropods in Antarctica. To survive low temperatures, mites and Collembola are freeze-intolerant and rely on deep supercooling, in some cases supercooling below −30°C. Also, some of these microarthropods are capable of cryoprotective dehydration to extend their supercooling capacity and reduce the risk of freezing. In contrast, the two best-studied Antarctic insects, the midges Belgica antarctica and Eretmoptera murphyi, are freeze-tolerant year-round and rely on both seasonal and rapid cold-hardening to cope with decreases in temperature. A common theme among Antarctic arthropods is extreme tolerance of dehydration; some accomplish this by cuticular mechanisms to minimize water loss across their cuticle, while a majority have highly permeable cuticles but tolerate upwards of 50–70% loss of body water. Molecular studies of Antarctic arthropod stress physiology are still in their infancy, but several recent studies are beginning to shed light on the underlying mechanisms that govern extreme stress tolerance. Some common themes that are emerging include the importance of cuticular and cytoskeletal rearrangements, heat shock proteins, metabolic restructuring and cell recycling pathways as key mediators of cold and water stress in the Antarctic.

Cold hardening processes in the Antarctic springtail, Cryptopygus antarcticus: clues from a microarray

The physiology of the Antarctic microarthropod, Cryptopygus antarcticus, has been well studied, particularly with regard to its ability to withstand low winter temperatures. However, the molecular mechanisms underlying this phenomenon are still poorly understood. 1180 sequences (Expressed Sequence Tags or ESTs) were generated and analysed, from populations of C. antarcticus. This represents the first publicly available sequence data for this species. A sub-set (672 clones) were used to generate a small microarray to examine the differences in gene expression between summer acclimated cold tolerant and non-cold tolerant springtails. Although 60% of the clones showed no sequence similarity to annotated genes in the datasets, of those where putative function could be inferred via database homology, there was a clear pattern of up-regulation of structural proteins being associated with the cold tolerant group. These structural proteins mainly comprised cuticle proteins and provide support for the recent theory that summer SCP variation within Collembola species could be a consequence of moulting, with moulting population having lowered SCPs.

Diurnal variation in supercooling points of three species of Collembola from Cape Hallett, Antarctica

Daily changes in microclimate temperature and supercooling point (SCP) of Collembola were measured during summer at Cape Hallett, North Victoria Land, Antarctica. Isotoma klovstadi and Cryptopygus cisantarcticus (Isotomidae) showed bimodal SCP distributions, predominantly in the high group during the day and in the low group during the night. There were no concurrent diurnal changes in water content or haemolymph osmolality. By contrast, Friesea grisea (Neanuridae) had a unimodal distribution of SCPs that was invariant between daytime and nighttime. Isotoma klovstadi collected foraging on moss had uniformly high SCPs, which shifted towards the low group when the animals were starved for 2-8 h. When I. klovstadi was acclimated for five days with lichen or algae, SCPs were higher than if they were supplied with moss, while those that were starved (with free water or 100% relative humidity) displayed a trimodal SCP distribution. A variety of pre-treatments, including cold, heat, desiccation and slow cooling were ineffective at inducing SCP shifts in C. cisantarcticus or I. klovstadi. It is postulated that behavioural avoidance of low temperatures by vertical migration may be key in I. klovstadi's short-term survival of nighttime temperatures. These data suggest that the full range of thermal responses of Antarctic Collembola is yet to be elucidated.

Seasonal changes in tolerance to cold and desiccation in Phauloppia sp. (Acari, Oribatida) from Finse, Norway

In the alpine region at Finse, Norway, Phauloppia spp. (Acari, Oribatida) inhabit lichens on top of boulders. Adult mites are about 0.5 mm in length and have a mean weight of ca. 15 µg. Temperatures in the lichens may drop below -35 degrees C in winter and increase to 55 degrees C in the summer. Large seasonal variations were recorded in supercooling points and body fluid osmolality. Mean January values of SCPs and osmolality were -35.3 degrees C and 3756 mOsm, while July values were -9.4 degrees C and 940 mOsm, respectively. Thermal hysteresis proteins were present in both summer and winter acclimated mites. In mid-winter, some of the mites survived more than 49 days in a water vapor saturated atmosphere at -19 degrees C, and more than 42 days enclosed in ice at the same temperature.The mites showed high tolerance to desiccation. Specimens collected in October survived up to 23 days at 22 degrees C and 5% RH. The tolerance to desiccation was lower in specimens collected during the winter. Some mites survived the loss of up to 90% of their total water content and were reactivated when given access to water. Length measurements of individual Phauloppia sp. showed that both male and female mites are clearly divided in two size groups, suggesting that they belong to two closely related species or different populations.