Environmental physiology of three species of Collembola at Cape Hallett, North Victoria Land, Antarctica

The environmental physiology of three speciesof Collembola: Cryptopygus cisantarcticus, Isotoma klovstadi (Isotomidae) and Friesea grisea (Neanuridae) was investigated from November 2002 to February 2003 at Cape Hallett, North Victoria Land, Antarctica. All three species were freeze avoiding, and while supercooling points were variable on seasonal and daily scales in I. klovstadi and C. cisantarcticus, they remained largely static in F. grisea. LT50 (temperature where 50% of animals are killed by cold) was -13.6, -19.1 and -19.8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, respectively. Upper lethal temperature was 34, 34 and 38 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Critical thermal minimum onset (the temperature where individuals entered chill coma) was ca. -7, -12 and -8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, and 25% of I. klovstadi individuals froze without entering chill coma. Critical thermal maximum (the onset of spasms at high temperature) was 30, 33 and 34 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Haemolymph osmolality was approximately 720 mOsm for C. cisantarcticus and 680 mOsm for I. klovstadi, and both species showed a moderate degree of thermal hysteresis, which persisted through the season. Desiccation resistance was measured as survival above silica gel, and the species survived in the rank order of C. cisantarcticus< I. klovstadi = F. grisea. Desiccation resulted in an increase in haemolymph osmolality in I. klovstadi, and water was quickly regained by desiccation-stressed individuals that had access to liquid water, but not by individuals placed in high humidity, indicating that this species is unable to absorb atmospheric water vapour. SDS-PAGE did not suggest any strong patterns in protein synthesis either seasonally or in response to temperature or desiccation stress. Microclimate temperatures were measured at sites representative of collection sites for the three species. Microclimate temperatures were highly variable on a diurnal and weekly scale (the latter relating to weather patterns), but showed little overall variation across the summer season. Potentially lethal high and low temperatures were recorded at several sites, and it is suggested that these temperature extremes account for the observed restriction of the less-tolerant C. cisantarcticus at Cape Hallett. Together, these data significantly increase the current knowledge of the environmental physiology of Antarctic Collembola.     

Terrestrial vegetation at Canada Glacier,Southern Victoria Land,Antarctica

Summary Bryophyte flushes in the vicinity of Canada Glacier in S.S.S.I. No. 12, Taylor Valley, Southern Victoria Land, were investigated in order to describe the vegetation present and to investigate factors affecting vegetation distribution. Biomass values from 950 to 1,250 g m^–2 (dry weight) and vegetated areas up to 14,450 m² indicate this is a significant area of bryophyte growth in Southern Victoria Land. The pattern of plant species in relation to water flow was investigated through detailed mapping. This is the first confirmed identification of Bryum argenteum, and Pottia heimii, and the first report of Bryum pseudotriquetrum from this area. Tissue nitrogen values for plants at this site are lower than other reported data, but it seems unlikely this would be a limiting factor for growth. It is concluded that, in this area, summer water flow in conjunction with microtopography has the greatest influence in determining where mosses, cyanobacteria and algae grow.     

Water geochemistry and sedimentary pigments in northern Victoria Land lakes,Antarctica

Total concentrations of algal pigments, organic C, C, N, P and S were determined in surface sediments from the littoral zone of 21 lakes in ice-free areas of northern Victoria Land (Antarctica) with different climatic and environmental conditions. Concentrations of major ions and nutrients were also determined in water samples from the same lakes. The latter samples had extremely variable chemical compositions; however, all the lakes resulted oligotrophic. Pigment concentrations in surface sediments were comparable to those reported for other Antarctic lakes and lower than those in oligotrophic lakes at lower latitudes. Cyanophyta, Chlorophyta and Bacillariophyta were the main taxa identified. These taxa correspond to those reported in previous microscopy-based studies on Antarctic phytoplankton and phytobenthos. Discriminant Function Analysis and Canonical Correspondence Analysis of data indicate that the distribution of pigments in these Victoria Land lakes depends mainly on their geographical location (particularly the distance from the sea) and nutrient status.     

Hexadecane mineralization activity in ornithogenic soil from Seabee Hook,Cape Hallett,Antarctica

Ornithogenic soils that form in penguin rookeries contain high levels of organic carbon and nitrogen. On Seabee Hook, Cape Hallett, Antartica, ornithogenic soil was contaminated with hydrocarbons following establishment of a scientific research station. In these soils hydrocarbon biodegradation could be supported by available soil nitrogen. Hexadecane mineralization activity was detected in vitro in ornithogenic soil when incubated at 5 or 15°C. At 5°C the extent of hexadecane mineralization was higher in hydrocarbon-contaminated soil than in uncontaminated soil. Alkane-degrading bacteria isolated from Seabee Hook soil were identified as Rhodococcus or Gordonia spp. or an unclassified Corynebacterineae. The alkane degraders grew on n-alkanes from heptane (C8) to eicosane (C20) and pristane, and utilized uric acid or ammonium nitrate as nitrogen source. All of the isolates possessed urease activity. Results of this study indicate biodegradation of hydrocarbons may contribute to the natural attenuation of oil spills in ornithogenic surface soils in summer.     

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.     

Benthic algal mats of some lakes of Inexpressible Island (northern Victoria Land,Antarctica)

 Benthic algal mats from four lakes located on Inexpressible Island (northern Victoria Land, Antarctica) were studied, analysing their structure and floristic composition. Thirty taxa of algae were identified: 11 Cyanophyta, 15 Bacillariophyta and 4 Chlorophyta. The lake mats contained from 15 (lake C) to 26 species (lake D). The number of diatom frustules in the mats varied from 771×10³ (lake C) to 9428×10³ frustules g^-1 (lake B). In terms of floristic composition and macromorphology, these mats were observed to be very similar to moat mats described from Lake Gondwana (northern Victoria Land) and the Dry Valleys lakes of southern Victoria Land. Received: 9 July 1995/Accepted: 12 February 1996     

Isolation of Bacillus thuringiensis from Northern Victoria Land, Antarctica

Sixty-two samples of Antarctic soils, mosses, penguin guano, algae and lichens were examined for the presence of aerobic endospore-forming bacteria; 36 samples (58%) yielded such organisms, and two samples from Edmonson Point (74 degrees 21'S 165 degrees 08'E) and one sample from Apostrophe Island (73 degrees 32'S 167 degrees 24'E), northern Victoria Land, yielded strains of Bacillus thuringiensis. Further isolations from two of the samples, appreciable variation in biotypes among the strains, failure of the strains to grow on routine B. thuringiensis media, and the fact that one of the sampling sites is very rarely visited by humans, suggest that the organisms were living in these soils rather than being chance contaminants. A representative strain, from Apostrophe Island, was identified as serovar pirenaica (H57).     

Assessing abundance and diversity patterns of soil microarthropod assemblages in northern Victoria Land (Antarctica)

This study aimed to: (1) assess differences between two quantitative sampling methods of soil microarthropods (visual census vs. stone washing) in ice-free areas located along a latitudinal gradient (from 72°37′S to 74°42′S) in northern Victoria Land (Antarctica); (2) furnish preliminary results on the abundance and diversity of mites and springtails in the studied areas. Visual census yielded reliable density estimates for adult collembolans and larger prostigmatic mites but did not detect small species. The study updates the distribution of several mites, including the southernmost record of an Oribatida species at global scale. Species composition was correlated with latitude but the uneven abundance distribution and local high beta-diversity probably reflect habitat fragmentation and population isolation. Under this circumstance nested sampling design should be usefully employed. Priorities and suitable methods for studying terrestrial microarthropod communities in continental Antarctica are discussed.     

Vegetation and ecology of ice-free areas of Northern Victoria Land,Antarctica

Summary At Birthday Ridge, a small ice free area in northern Victoria Land (70°48S, 167°00E), cryptogamic vegetation is mostly confined to gaps between granitc rocks. The sheltering effect on lichens and mosses was analyzed by continuous measurements of the microclimate at various levels between the rocks. Although warming by solar radiation was favourable for the existence of cryptogams, rocks strongly insolated were mostly devoid of lichens and mosses. Lichens in the soaked active state were heated to above air temperature but did not reach more than 10°C. The presence of lichens was dependent on the moisture conditions of the habitat. It was observed that snow, the only source of moisture, accumulated in summer only in deeper levels between rocks, and that the snow rapidly melted on contact with the lichens. After a snow shower,Usnea sulphurea gained 67% andUmbilicaria decussata 94% of their maximum water capacity. During one quarter of the time period of 7 days the lichens were soaked and therefore capable of carrying out photosynthesis. The lichens in soaked state had always less than optimum temperatures for net photosynthesis. The rock gaps at Birthday Ridge form oases, the only localities where moisture is provided, and temperature is high enough to enable growth of lichens and mosses.Bryum is also able to exist in the upper 3 cm of soil.     

Ecological Biogeography of the Terrestrial Nematodes of Victoria Land,Antarctica

The terrestrial ecosystems of Victoria Land, Antarctica are characteristically simple in terms of biological diversity and ecological functioning. Nematodes are the most commonly encountered and abundant metazoans of Victoria Land soils, yet little is known of their diversity and distribution. Herein we present a summary of the geographic distribution, habitats and ecology of the terrestrial nematodes of Victoria Land from published and unpublished sources. All Victoria Land nematodes are endemic to Antarctica, and many are common and widely distributed at landscape scales. However, at smaller spatial scales, populations can have patchy distributions, with the presence or absence of each species strongly influenced by specific habitat requirements. As the frequency of nematode introductions to Antarctica increases, and soil habitats are altered in response to climate change, our current understanding of the environmental parameters associated with the biogeography of Antarctic nematofauna will be crucial to monitoring and possibly mitigating changes to these unique soil ecosystems.     

Microbial community composition in soils of Northern Victoria Land, Antarctica

Biotic communities and ecosystem dynamics in terrestrial Antarctica are limited by an array of extreme conditions including low temperatures, moisture and organic matter availability, high salinity, and a paucity of biodiversity to facilitate key ecological processes. Recent studies have discovered that the prokaryotic communities in these extreme systems are highly diverse with patchy distributions. Investigating the physical and biological controls over the distribution and activity of microbial biodiversity in Victoria Land is essential to understanding ecological functioning in this region. Currently, little information on the distribution, structure and activity of soil communities anywhere in Victoria Land are available, and their sensitivity to potential climate change remains largely unknown. We investigated soil microbial communities from low- and high-productivity habitats in an isolated Antarctic location to determine how the soil environment impacts microbial community composition and structure. The microbial communities in Luther Vale, Northern Victoria Land were analysed using bacterial 16S rRNA gene clone libraries and were related to soil geochemical parameters and classical morphological analysis of soil metazoan invertebrate communities. A total of 323 16S rRNA gene sequences analysed from four soils spanning a productivity gradient indicated a high diversity (Shannon-Weaver values > 3) of phylotypes within the clone libraries and distinct differences in community structure between the two soil productivity habitats linked to water and nutrient availability. In particular, members of the Deinococcus/Thermus lineage were found exclusively in the drier, low-productivity soils, while Gammaproteobacteria of the genus Xanthomonas were found exclusively in high-productivity soils. However, rarefaction curves indicated that these microbial habitats remain under-sampled. Our results add to the recent literature suggesting that there is a higher biodiversity within Antarctic soils than previously expected.     

Diversity of Soil Yeasts Isolated from South Victoria Land,Antarctica

Unicellular fungi, commonly referred to as yeasts, were found to be components of the culturable soil fungal population in Taylor Valley, Mt. Discovery, Wright Valley, and two mountain peaks of South Victoria Land, Antarctica. Samples were taken from sites spanning a diversity of soil habitats that were not directly associated with vertebrate activity. A large proportion of yeasts isolated in this study were basidiomycetous species (89%), of which 43% may represent undescribed species, demonstrating that culturable yeasts remain incompletely described in these polar desert soils. Cryptococcus species represented the most often isolated genus (33%) followed by Leucosporidium (22%). Principle component analysis and multiple linear regression using stepwise selection was used to model the relation between abiotic variables (principle component 1 and principle component 2 scores) and yeast biodiversity (the number of species present at a given site). These analyses identified soil pH and electrical conductivity as significant predictors of yeast biodiversity. Species-specific PCR primers were designed to rapidly discriminate among the Dioszegia and Leucosporidium species collected in this study.     

Growth temperature preferences of fungal strains from Victoria Land,Antarctica

Thirty-five strains of microfungi, isolated from various sites in Victoria Land, Antarctica, were grown at eight temperatures ranging from 0 to 45°C. Only 1 strain (Chaetomium sp. from hot soil) was a thermotolerant mesophile; other strains were psychrophilic (2 strains) or psychrotrophic (32 strains). The fitness of different species to thermal instability is discussed, based on the width of the growth rate curves.     

Dicroidium diversity in the Upper Triassic of north Victoria Land,East Antarctica

We describe an assemblage of well-preserved, cuticle-bearing plant compressions collected from a single bed in the Upper Triassic of Timber Peak, East Antarctica. The flora is dominated by the seed fern Dicroidium, a morphogenus that is widespread and usually dominant in Middle to Late Triassic plant assemblages throughout Gondwana. Despite its common occurrence, the systematic classification of Dicroidium and its individual species remains problematic. This study demonstrates that a combination of macromorphological and cuticular features enables a suitable discrimination of Dicroidium species. The present Dicroidium assemblage is remarkably diverse and dominated by D. elongatum with subordinate proportions of D. odontopteroides, D. crassinervis, and a new species provisionally named D. sp. A. In addition, D. dubium, D. spinifolium, and D. coriaceum occur sporadically. We reinstitute D. spinifolium and propose an emended diagnosis. Other taxa present include putative bryophyte remains, Lepidopteris langlohensis, and Heidiphyllum elongatum. Another collection of plant fossils from a second plant-bearing horizon at Timber Peak consists of fragmentary remains of Cladophlebis sp. and H. elongatum. Epidermal and cuticular features of the Dicroidium fronds suggest that this flora flourished under favourable climatic conditions, although it was situated at latitudes of about 70° S and must have experienced long annual periods of darkness during the austral winter. The cuticles studied point to a short leaf lifespan and very high photosynthetic performance of Dicroidium fronds. We suggest that this leaf phenology has facilitated the Dicroidium plants to colonize the polar latitudes of the Triassic greenhouse world so successfully.     

Invertebrates associated with moss communities at Canada Glacier,southern Victoria Land,Antarctica

The invertebrate faunal composition of moss-dominated flushes near the Canada Glacier was, as in similar habitats in continental Antarctic regions, numerically dominated by protozoa, rotifers, nematodes and tardigrades. Mites were of lesser abundance. Although collembola occur in the Taylor Valley, none were found at the study site. The finding of a catenulid flatworm is significant as microturbellarians have only rarely been recorded from Antarctica. Nematode, tardigrade and rotifer densities recorded were comparable to those in other Antarctic regions. These groups were found at a mean depth ranging from 5 to 10.83 mm in the moss. A greater percentage of all groups were in the upper 5 mm of moss cores in post-melt samples than in pre-melt samples.     

Geochemical processes in the Lake Fryxell Basin (Victoria Land,Antarctica)

Major ion, nutrient, transition metal, and cadmium concentrations are presented for nine meltwater streams flowing into Lake Fryxell, a permanently stratified lake with an anoxic hypolimnion in Taylor Valley, Antarctica. For the major ions, stream compositions are considered in terms of dissolution of marine-derived salts and chemical weathering of local rocks. Although Lake Fryxell has undergone significant evaporative concentration, only calcite, of the simple salts, is predicted to precipitate. Geochemical budgets indicate, however, that large quantities of K, Mg, and SO₄ have also been removed from the lake. Reverse weathering may be an important sink for K and Mg, although magnesium removal with calcium carbonate phases is also likely. Assuming constancy of composition over recent geologic time, all of the salts in the Fryxell water column could have been delivered under present flows in about three thousand years (chloride age).Comparison of nutrient concentrations in these meltwater streams with other flowing waters in the world reveals that the Fryxell streams are strikingly deficient in NO₃-N but not PO₄-P. The apparent nitrogen deficiency in Lake Fryxell itself can be attributed to the low annual stream loadings of this nutrient.Stream concentrations and loadings are also presented for Mn, Fe, Co, Ni, Cu, and Cd. Dissolved metal concentrations correlate roughly with average crustal abundances, suggesting that chemical weathering is the major source for these elements. Vertical metal profiles within Lake Fryxell itself appear to be governed by the formation of insoluble sulfide phases, or, in the case of Mn, by MnHPO₄. However, dissolved nickel levels in sulfide-bearing waters are much higher than can be explained in terms of metal-sulfide equilibria, and we suspect that significant organic complexing of this metal is occurring in the deeper waters.     

Environmental correlates of vegetation patterns and species richness in the northern Grampians,Victoria

Abstract Plant species cover-abundance and density data were collected for 94 sample plots across a gradient from rocky uplands to sandy outwash plains in the northern part of Grampians (Gariwerd) National Park in western Victoria. Detrended correspondence analysis (DCA) was used to identify dominant gradients in species composition. A range of static (e.g. substrate type, soil depth, microclimate indicators) and dynamic (e.g. elapsed time since last fire) environmental variables were measured. Correlations were sought between these variables and vegetation patterns including those for richness (R) and Shannon-Weiner diversity (H′). The dominant gradient of vegetation change identified by DCA separated rocky sites and sites near ephemeral streams, from well-drained, sandy sites. Secondary gradients identified time since last fire as important for sandy sites, and altitude and aspect-related microclimate for rocky sites. Diversity was highest in the first 2 years after fire but showed no further decline in older sites. Overall, R and H' were negatively correlated with soil nutrient concentrations. On sandy sites R was high, but was low on rocky sites and near streams. Within the rocky sites, R was highest on cool, moist south and east slopes, and lowest on hot, dry north and west slopes. Explanations of diversity patterns based on inhibition of competitive exclusion due to stress and recurrent disturbance best fit the results presented here.     

Patterns of population genetic structure for springtails and mites in southern Victoria Land, Antarctica

We sequenced the mitochondrial (mt) DNA cytochrome c oxidase subunit I gene to examine comparative phylogeographic patterns for the springtail Gomphiocephalus hodgsoni and the mite Stereotydeus mollis throughout their ranges in southern Victoria Land, Antarctica. Our aim was to extend previous genetic work to encompass a large ice-free area in the Dry Valleys. In particular, we sought to determine if this new region harboured high levels of genetic diversity and if patterns of genetic structure were congruent across taxa. Phylogenetic and nested clade analyses for G. hodgsoni and S. mollis showed similar patterns of population sub-structuring among locations and highlighted several potential refugia that may have existed during glacial maxima. We identified greater levels of genetic divergence in S. mollis and suggest that there is a nucleotide substitution (mutation) rate difference between S. mollis and G. hodgsoni, and/or that S. mollis has had a longer association with the Antarctic landscape.