Changes in lichen diversity and community structure with fur seal population increase on Signy Island, South Orkney Islands

Signy Island has experienced a dramatic increase in fur seal numbers over recent decades, which has led to the devastation of lowland terrestrial vegetation, with the eradication of moss turfs and carpets being the most prominent feature. Here we demonstrate that fur seals also affect the other major component of this region’s typical cryptogamic vegetation, the lichens, although with a lower decrease in variability and abundance than for bryophytes. Classification (UPGMA) and ordination (Principal Coordinate Analysis) of vegetation data highlight differences in composition and abundance of lichen communities between areas invaded by fur seals and contiguous areas protected from these animals. Multivariate analysis relating lichen communities to environmental parameters, including animal abundance and soil chemistry (Canonical Correspondence Analysis), suggests that fur seal trampling results in the destruction of muscicolous-terricolous lichens, including several cosmopolitan and bipolar fruticose species. In addition, animal excretion favours an increase in nitrophilous crustose species, a group which typically characterizes areas influenced by seabirds and includes several Antarctic endemics. The potential effect of such animal-driven changes in vegetation on the fragile terrestrial ecosystem (e.g. through modification of the ground surface temperature) confirms the importance of indirect environmental processes in Antarctica

Diapause induces remodelling of the fatty acid composition of membrane and storage lipids in overwintering larvae of Ostrinia nubilalis, Hubn. (Lepidoptera: Crambidae)

Seasonal changes in the FA composition of triacylglycerols and phospholipids prepared from the whole body of non-diapausing and diapausing fifth instar larvae of Ostrinia nubilalis, Hubn. (Lepidoptera: Crambidae) were determined to evaluate the role of these lipids in diapause. Substantial changes in the FA composition of triacylglycerols and phospholipids were triggered by diapause development. This led to a significant increase in the overall FA unsaturation (UFAs/SFAs ratio), attributable to an increase in the relative proportion of MUFAs and the concomitant decrease in PUFAs and SFAs. In triacylglycerols, the significant changes in FAs composition is the result of an increase in the relative proportions of MUFAs, palmitoleic acid (16:1n-7) and oleic acid (18:1n-9), and a concomitant reduction in composition of SFAs and PUFAs, mainly palmitic acid (16:0) and linoleic acid (18:2n-6), respectively. Changes in the composition of phospholipids were more subtle with FAs contributing to the overall increase of FA unsaturation. Differential scanning calorimetry (DSC) analysis revealed that the melt transition temperatures of total lipids prepared from whole larvae, primarily attributable to the triacylglycerol component, were significantly lower during the time course of diapause compared with non-diapause. These observations were correlated to the FA composition of triacylglycerols, most likely enabling them to remain functional during colder winter conditions. We conclude that O. nubilalis undergoes remodelling of FA profiles of both energy storage triacylglycerols and membrane phospholipids as an element of its overwintering physiology which may improve the ability to cold harden during diapause

Ecology of moss banks on Signy Island (maritime Antarctic)

Mosses are dominant components of high-latitude environments, and Signy Island (maritime Antarctic) provides a representative example of polar cryptogam-dominated terrestrial ecosystems. In 2011, we mapped all moss banks, their characteristics (thickness, area, floristic composition) and investigated their relationship with selected environmental factors including topography (elevation, slope, aspect), biotic disturbance (fur seals), deglaciation age of the surfaces, location on the eastern vs. western side of the island and snow cover as a proxy of water supply during the summer (December). We here identify the most important environmental factors influencing moss bank characteristics and distribution and provide a baseline for future monitoring. Moss bank abundance and distribution are the result of the interaction of multiple abiotic and biotic factors acting at different spatial scales. The most important factors are the location of moss banks on the eastern vs. western side of the island at the macroscale (with thicker and larger moss banks and a prevalence of Chorisodontium aciphyllum on the western side) and their favourable aspect (mainly N, NW) at the microscale, providing better microclimatic conditions suitable for their development. The elevation threshold detected at 120 m could indicate the occurrence of a ‘moss bank line’, analogous to the tree line, and corresponds with a threshold of mean annual temperature of −4.8 °C. The other factors examined play a subsidiary role in affecting bank distribution and characteristics. These findings allow a better understanding of this key feature of maritime Antarctic vegetation and provide quantitative information about their ecology

Surviving the cold: molecular analyses of insect cryoprotective dehydration in the Arctic springtail Megaphorura arctica (Tullberg)

<p>Abstract</p> <p>Background</p> <p>Insects provide tractable models for enhancing our understanding of the physiological and cellular processes that enable survival at extreme low temperatures. They possess three main strategies to survive the cold: freeze tolerance, freeze avoidance or cryoprotective dehydration, of which the latter method is exploited by our model species, the Arctic springtail <it>Megaphorura arctica</it>, formerly <it>Onychiurus arcticus </it>(Tullberg 1876). The physiological mechanisms underlying cryoprotective dehydration have been well characterised in <it>M. arctica </it>and to date this process has been described in only a few other species: the Antarctic nematode <it>Panagrolaimus davidi</it>, an enchytraied worm, the larvae of the Antarctic midge <it>Belgica antarctica </it>and the cocoons of the earthworm <it>Dendrobaena octaedra</it>. There are no in-depth molecular studies on the underlying cold survival mechanisms in any species.</p> <p>Results</p> <p>A cDNA microarray was generated using 6,912 <it>M. arctica </it>clones printed in duplicate. Analysis of clones up-regulated during dehydration procedures (using both cold- and salt-induced dehydration) has identified a number of significant cellular processes, namely the production and mobilisation of trehalose, protection of cellular systems via small heat shock proteins and tissue/cellular remodelling during the dehydration process. Energy production, initiation of protein translation and cell division, plus potential tissue repair processes dominate genes identified during recovery. Heat map analysis identified a duplication of the trehalose-6-phosphate synthase (TPS) gene in <it>M. arctica </it>and also 53 clones co-regulated with TPS, including a number of membrane associated and cell signalling proteins. Q-PCR on selected candidate genes has also contributed to our understanding with glutathione-S-transferase identified as the major antioxdidant enzyme protecting the cells during these stressful procedures, and a number of protein kinase signalling molecules involved in recovery.</p> <p>Conclusion</p> <p>Microarray analysis has proved to be a powerful technique for understanding the processes and genes involved in cryoprotective dehydration, beyond the few candidate genes identified in the current literature. Dehydration is associated with the mobilisation of trehalose, cell protection and tissue remodelling. Energy production, leading to protein production, and cell division characterise the recovery process. Novel membrane proteins, along with aquaporins and desaturases, have been identified as promising candidates for future functional analyses to better understand membrane remodelling during cellular dehydration.</p

Inhibitory effects of climate change on the growth and extracellular enzyme activities of a widespread Antarctic soil fungus

Temperatures approaching or exceeding 20 °C have been measured during summer in polar regions at the surfaces of barren fellfield soils under cloudless skies around solar noon. However, despite the upper temperature limit for the growth of cold‐adapted microbes – which are abundant in polar soils and have pivotal roles in nutrient cycling – typically being close to this temperature, previous studies have not addressed the consequences of climate change for the metabolism of these organisms in the natural environment. Here, in a five‐year field experiment on Alexander Island in the southern maritime Antarctic, we show that the abundance of Pseudogymnoascus roseus, the most widespread decomposer fungus in maritime Antarctic fellfield soils, is reduced by 1–2 orders of magnitude when irrigated and nutrient‐amended soils are warmed to >20 °C during summer. Laboratory experiments under conditions mimicking those during midsummer in the natural environment indicated that the hyphal extension rates of P. roseus isolates and the activities of five extracellular enzymes are reduced by 54–96% at high water availability after exposure to temperatures cycling daily from 2–21 °C and 2–24 °C, relative to temperatures cycling from 2–18 °C. Given that the temperatures of surface soils at the study site already reach 19 °C during midsummer, the observations reported here suggest that, at predicted rates of warming arising from moderate greenhouse gas emissions, inhibitory effects of climate change on the metabolism of P. roseus could manifest themselves within the next few decades. Furthermore, with peak temperatures at the surfaces of fellfield soils at other maritime Antarctic locations and in High Arctic and alpine regions already exceeding 20 °C during summer, the observations suggest that climate warming has the potential to inhibit the growth of other cold‐adapted microbes, with negative effects on soils as the Earth’s climate continues to war

Spatial distribution, habitat preference and colonization status of two alien terrestrial invertebrate species in Antarctica

The introduction of invasive species is one of the greatest threats to Earth’s biodiversity, as they can reduce native biodiversity and alter ecosystem structure and function. Currently, the only two known non-native terrestrial invertebrates in Antarctica are the chironomid midge Eretmoptera murphyi and the enchytraeid worm Christensenidrilus blocki. These invertebrates were probably introduced to ground near Signy Research Station, South Orkney Islands, during transplantation experiments in the late 1960s. Between 2007 and 2009, this study surveyed the area around the introduction site for midge larvae and worms to assess any change over the last four decades in their spatial distribution, habitat preference and colonization status. Eretmoptera murphyi was found in concentrations up to 4.1 × 105 larvae m-2 (mean 2.1 × 104 larvae m-2) at distances of up to 220 m from the probable introduction site (c. 35 000 m2), while C. blocki was only found close to the introduction site in low numbers. Significantly more E. murphyi larvae were found in peat and dead organic material (3.34 × 104 m-2) than in stony soil and gravel (1.52 × 104 m-2) or living moss and other plant material (1.16 × 104 m-2). Eretmoptera murphyi can no longer be considered a persistent alien as it clearly expanding its distribution, while C. blocki remains a persistent alien species

Factors that influence freezing in the sub-Antarctic springtail Tullbergia antarctica

Effects of 12 biotic and abiotic factors on the freezing point of the sub-Antarctic springtail, Tullbergia antarctica, were investigated. Repeated cooling of individual springtails five times resulted in very similar freezing points suggesting that ice nucleation in this freeze-susceptible species is likely to be initiated by intrinsic factors rather than being a stochastic event. Mean supercooling point (SCP) was influenced by cooling protocol, showing a linear increase in mean SCP with cooling rates from 8 to 0.1 °C min−1. However, the opposite effect (decreasing SCP) was seen with slower cooling. Slower rates may be ecologically realistic and allow time for appropriate physiological and biochemical changes. Feeding and food presence in the gut had no effect on SCP, and there was no correlation between the ice nucleating activity of bacteria isolated from the guts and the whole springtail SCP. Habitat altitude and diurnal light and temperature regimes also had no effect on SCP. There was no correlation between the cryoprotectant concentration of fresh animals and their SCP, but experimental desiccation resulted in increased osmolality and decreased SCP, although with considerable individual variation. The most significant influence on SCP was associated with ecdysis. As springtails cease feeding for a period either side of ecdysis, shedding the entire gut lining, moulting may be an efficient mechanism of clearing the gut of all ice nucleating material. This previously unrecognised relationship between ecdysis, cold tolerance and seasonal survival tactics may play an important role in over-winter survival of some arthropods

The relationship between water content and cold tolerance in the arctic collembolan Onychiurus arcticus (Collembola: Onychiuridae)

The arctic collembolan Onychiurus arcticus is freezing intolerant and experiences temperatures below -25°C during winter periods of low air temperatures and only light snow cover. Summer-collected individuals have a mean (±SE) supercooling point of -6.1 ± 0.1°C. This study was designed to measure the desiccation resistance and subsequent recovery of O. arcticus from partial dehydration and relate these to its cold-hardiness in terms of changes in the supercooling point (SCP) and solute concentration. Drying curves measured with a recording microbalance showed two distinct phases characteristic of the loss of free and chemically bound (osmotically inactive) water. Rates of water loss at 0°C and low relative humidity (< 5%) were similar to those measured for Antarctic Collembola (5% h-1 of the initial total water content). O. arcticus survived losses of 40% of its total body water content and recovered within 36 h but could not survive losses of 50% of its original water content. Differential scanning calorimetry was used to investigate the nature of the body water, i.e. the proportion of freezable to unfreezable water and the nucleation temperature. The melt onset temperature correlated positively with the body water content. But no clear relationship was seen between the water content and the SCP, either because the springtails had low levels of cryoprotectants or because the ice nucleation activity was unaffected. However, long periods (7 months) at -2.5°C reduced the water content from 74 ± 10.1 to 43 ± 7.2% of fresh weight and lowered the SCP from -6.1 ± 2.1 to -15.5 ± 2.3°C. When given access to water these individuals re-gained their body weight within 24 h. During periods of desiccation water losses were attributed to the loss of freezable water with the unfreezable portion remaining almost constant at 16.5 ± 2.0%. It appears that O. arcticus may experience a reduction of body water during winter periods of sub-zero temperatures, which may lower its SCP and enhance its cold tolerance but that it can rapidly return to summer levels given access to free water during the spring melt

Ice-nucleating bacteria from the guts of two sub-Antarctic beetles,Hydromedion sparsutum and Perimylops antarcticus(Perimylopidae)

The site of ice nucleation in the freeze-tolerant, sub-Antarctic beetleHydromedion sparsutumhas been investigated. Ice+bacteria, active at above −2.0°C, were isolated from the guts of beetles and identified as a fluorescentPseudomonasspecies. Other possible sites of nucleation, including the hemolymph, were examined but had a lower activity. Ice+bacteria were isolated from mixed populations, isolated from the guts of adult beetles, and grown on nutrient agar plates and in nutrient broth. Nucleation activity of the broth culture peaked after only 2 days although the number of live cells continued to increase until day 6. These cultures were used to determine the maximum nucleation activity of a bacterial suspension in sterile distilled water (−3.4°C) and the dilution factor required to cause a 50% reduction in activity (104). The original bacterial suspension had an absorbance of 0.5 measured at 660 nm and contained 6 × 1011bacteria per milliliter. From this it is estimated that only 1 in 106bacteria possessed the highest levels of ice-nucleating activity. Other insect species, including Perimylops antarcticus,which are found in habitats similar to that ofH. sparsutum,were examined for the presence of ice+bacteria. All contained ice-nucleating bacteria in their guts but with a lower level of activity than in H. sparsutum

An Automatic Respirometer for use with Small Invertebrates

1. An automatic respirometer is described which has been developed to measure the rate of oxygen consumption by small arthropods in closed chambers. 2. The instrument removes 0.5 \mul subsamples of air from the head space of specially designed sample chambers using a precision sampling valve and a motorized syringe. The prototype can monitor up to 10 sample chambers automatically over periods of several hours, using an electronic sequence switch to control the operation. 3. Oxygen concentration is measured using a coulometric fuel cell which produces an output signal directly proportional to the mass of oxygen passing over it and requires no calibration. The results are recorded on an integrator of the type commonly used with gas chromatographs. 4. The sensitivity of the respirometer is better than 1 \mul h-1 when small chambers (1-2 ml) are monitored over 3-4 h. 5. The instrument is also capable of measuring the volume of the sample chambers to an accuracy of c. 2% allowing the volume of oxygen consumed by the sample to be calculated. 6. The instrument may be modified to measure the oxygen concentration in the head space of almost any container and would operate on a low-voltage DC supply for field operation