Genetic variation in Antarctic populations of the moss Sarconeurum glaciale

Sixty-six isolates of the moss Sarconeurum glaciale were collected from sites in continental Antarctica at Ross Island, southern Victoria Land and the Vestfold Hills. Genetic variation within and among the populations was estimated using isozymes and random amplified polymorphic DNA (RAPD) technology. Isozyme results only reproducibly showed variation between the populations with one enzyme; RAPDs indicated significantly higher levels of genetic variability within and among the Vestfold Hills samples than in the Ross Sea region samples. A dendrogram produced from the RAPD bands suggested that the Ross Island and southern Victoria Land samples form one population, and those from the Vestfold Hills form a separate and more variable population, possibly resulting from separate colonisation events on the continent. Received: 15 March 1996 / Accepted: 1 May 1997     

RAPD analysis of genetic variation and dispersal of the moss Bryum argenteum in Ross Island and Victoria Land, Antarctica

The Random Amplified Polymorphic DNA technique was used to assess the level of genetic diversity in Bryum argenteum from Ross Island and southern Victoria Land, Antarctica. Samples were collected from three separate transects, and from other geographically distinct populations within 150 km of Ross Island. Moss growth in two transects, sampled down small exposed meltstream channels at Cape Royds and Cape Chocolate, was very sparse with no other moss colonies found within 0.4 or 4 km, respectively. However, samples from these channels showed similar levels of genetic variation to those from a transect at Granite Harbour, where moss colonies were large, luxuriant and turf-like between boulders. In all transects, high levels of genetic diversity were apparent both within and between colonies, and some spatial relationships were observed down the length of the channels, with more extensive variation at the top than the bottom of two transects. Samples from other sites in the region showed varying but high levels of genetic diversity; overall, the majority showed some clustering according to site of collection, with short-distance dispersal of propagules by water and transmission between sites presumably by wind. The extensive genetic diversity observed appears mainly due to somatic mutation within colonies, with some contribution by immigration of propagules from elsewhere into established colonies. Accepted: 10 January 1999     

Genetic diversity in the moss Pohlia nutans on geothermal ground of Mount Rittmann, Victoria Land, Antarctica

The only known population of the moss Pohlia nutans in continental Antarctica occurs on geothermally heated ground of volcanic Mt. Rittmann in northern Victoria Land. Colonisation by this bryophyte is due to peculiar environmental characteristics of the geothermal ground, because mosses do not normally grow in Antarctica at such elevations. Specimens from several moss patches within two sites of 80 m² total area were analysed genetically to determine whether they all originated from a single colonisation event, whether the population is genetically diverse, and whether the temperature range of geothermal ground (17-35°C under moss colonies) affects rates of mutation. Both the RAPD technique and DNA sequencing of the conserved nuclear ribosomal RNA 18S-26S ITS region were used to compare this extremely isolated population with specimens of P. nutans from elsewhere in Antarctica. Like the moss Campylopus pyriformis on volcanic Mt. Melbourne, the Pohlia population exhibits low levels of genetic diversity and appears to be derived from a single immigration event followed by vegetative growth, mutation and dispersal.     

RAPD analysis of genetic variation and dispersal of the moss Bryum pseudotriquetrum from Southern Victoria Land, Antarctica

The RAPD technique (Random Amplified Polymorphic DNA) was used to assess the level of genetic diversity in Bryum pseudotriquetrum from Southern Victoria Land, Antarctica. Isolates were collected from two transects, and from several other geographically distinct populations within 150 km of Ross Island. Moss growth in one transect, sampled down a small exposed meltstream channel at Cape Chocolate, was very sparse with no other moss colonies found within several hundred meters. Isolates from this transect showed low levels of genetic variation, with many moss clumps appearing identical; these were probably dispersed by water along the channel. In another transect analysed from Granite Harbour, the moss colonies were large, luxuriant and protected by boulders. These isolates showed considerably higher levels of genetic variability than the Cape Chocolate samples, and both within- and between-clump variation was observed. Samples from other sites showed varying levels of genetic diversity. It appears from these results that the degree of protection from the harsh Antarctic environment can influence not only the type of moss growth, but also the level of genetic diversity. Evidence is presented for both short-distance dispersal by water and long-distance dispersal by wind. Received: 29 December 1997 / Accepted: 10 April 1998     

RAPD profiling of genetic diversity in two populations of the moss Ceratodon purpureus in Victoria Land, Antarctica

Isolates of the moss Ceratodon purpureus were collected down a channel formed by a meltstream waterfall at Granite Harbour in Southern Victoria Land, Antarctica. The RAPD technique was used to analyse the extent of genetic variation within clumps, between clumps, and between this population and specimens of the same species from two other areas in Antarctica (one a few hundred metres away, the other at Edmonson Point, 300 km further north) and from Sydney, Australia. Genetic variation was detected within and among clumps, with some spatial structure to the population within the channel. Isolates from the nearby location were quite closely related, whereas those from Edmonson Point formed an outgroup on a phylogenetic tree of relatedness. Received: 10 June 1997 / Accepted: 30 September 1997     

Genetic diversity and dispersal of the moss Sarconeurum glaciale on Ross Island, East Antarctica

The extent of genetic variation and dispersal mechanisms were investigated over short distances of 1–100 m, and up to 3 km, by the random amplified polymorphic DNA (RAPD) technique, for the moss Sarconeurum glaciale , at three locations on Ross Island, Antarctica. At Arrival Heights, genetic variation occurred within single colonies, and the relationships between clumps indicated that they were dispersed down small, meltwater drainage channels by water. The genetic similarities between the colonies from Arrival Heights and others from Scott Base and Crater Hill, a few km away, together with the prevailing wind direction and absence of this moss in the intervening snow-covered area, suggested longer-distance dispersal by wind. Overall, the Ross Island samples appeared to form a single, polymorphic population that was distinct from another population at Canada Glacier, 110 km distant. Somatic mutation, rather than immigration of genetically different propagules from elsewhere, appeared to be the most probable cause of genetic variability in these haploid, vegetatively reproducing Antarctic moss populations. Initiation of recolonization of S. glaciale across a dirt track at Arrival Heights was also investigated by RAPDs, to investigate how regrowth of mosses in disturbed areas occurred in the extreme environment of Antarctica.     

Temperature-related activity of <Emphasis Type="Italic">Gomphiocephalus hodgsoni</Emphasis> (Collembola) mitochondrial DNA (COI) haplotypes in Taylor Valley,Antarctica

Gomphiocephalus hodgsoni (Collembola) is the most common and widely distributed arthropod in the Dry Valleys of southern Victoria Land, and is genetically diverse with over 70 mitochondrial cytochrome c oxidase subunit I (COI) haplotypes. There is also considerable physiological variation among G. hodgsoni individuals in their cold tolerance and metabolic activity. Here, we assessed genetic haplotypes of G. hodgsoni relative to the environmental conditions during which individuals were active. We sequenced the COI region of 151 individuals collected in pitfall traps from three sites within Taylor Valley and found 19 unique haplotypes that separated into two distinct lineages (1.6 % divergence), with one lineage comprising 80 % of the sequenced population. During two-hourly sampling, air temperature was the strongest predictor of activity between the two lineages (R ² = 0.56), and when combined with subsurface soil temperature, relative humidity and photosynthetically active radiation, explanatory power increased to R ² = 0.71. With steadily increasing air temperatures predicted for much of Antarctica, it is likely that some haplotypes will have a selective advantage and potentially result in decreased genetic variability within populations. We suggest that temporal monitoring of the relative proportions of COI haplotypes or other appropriate genetic markers may provide a subtle measure of biological responses to environmental changes within Antarctic terrestrial ecosystems.     

The southernmost worm, <Emphasis Type="Italic">Scottnema lindsayae</Emphasis> (Nematoda): diversity,dispersal and ecological stability

The nematode worm Scottnema lindsayae (Cephalobidae) was found near the base of the Beardmore Glacier in the Transantarctic Mountains 83.48°S, over 5° further south than previously recorded. Identification was confirmed using morphological analyses of males, females and juvenile stages, and by DNA sequencing of the ITS1 region of the ribosomal RNA tandem repeat unit. These data revealed no discernable morphological or ITS rDNA sequence variation between the extreme southern population of S. lindsayae and disparate populations from the McMurdo Dry Valleys in south Victoria Land (77–78°S). Based on these results, we suggest that broadcast dispersal, with accompanying high rates of gene flow, establish the extreme southern distribution of the phylum Nematoda. High abundance, low rates of diversification and lack of an apparent biogeographic structure across latitudinal and environmental gradients implies that their presence in simple Antarctic soil ecosystems is stable, so long as physical and biological controls on their distributions remain within viable parameters. Recent evidence that S. lindsayae populations are in decline suggests that their high dispersal rates are insufficient to buffer current, unfavorable environmental changes and may foreshadow longer-term ecosystem disruption.     

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.     

Fine scale distribution of mtDNA haplotypes for the springtail Gomphiocephalus hodgsoni (Collembola) corresponds to an ancient shoreline in Taylor Valley, continental Antarctica

We examined the fine scale distribution of the endemic Antarctic collembolan Gomphiocephalus hodgsoni in Taylor Valley, southern Victoria Land using the mitochondrial DNA cytochrome c oxidase I gene. We found an area of sympatry in the mid-region of the valley between two common haplotype groups (2.4% sequence divergence). The area of sympatry coincided with the extent of proglacial Lake Washburn (approx. 8,000 ya). This lake existed as a result of the damming of lower Taylor Valley by the grounding of the Ross Ice Sheet and may have acted as an isolating barrier to dispersal/gene flow. We suggest that the phylogenetic break occurring in the vicinity of the ancient shoreline may be the result of previous isolation of refugial allopatric populations, followed by recolonisation into a secondary contact zone during the Holocene.     

Variation in the ribosomal ITS-sequence of the lichens Buellia frigida and Xanthoria elegans from the Vestfold Hills,eastern Antarctica

Abstract:Thalli of the lichens Buellia frigida and Xanthoria elegans were collected from five different locations each 5–15 km apart in the Vestfold Hills, Princess Elizabeth Land, eastern Antarctica. A further collection was made from Mawson Station, Mac Robertson Land, eastern Antarctica, 660 km away. DNA was extracted from whole thalli and the ribosomal ITS region amplified by PCR using fungal specific primers. Resulting products were sequenced to gain an indication of whether or not variation was present within populations of lichen-forming fungi from continental Antarctica, and therefore of the availability of genetic resources to react to pressures such as climate change. Three genotypes ofB. frigida and two of X. elegans were detected in the Vestfold Hill collections. However, these differed by only one nucleotide position suggesting the presence of relatively little genetic variation, if the ITS region is indicative of the overall genome. Buellia frigida collected from Mawson Station had an identical ITS region sequence to the most common Vestfold Hills genotype, indicating that this species may have a low level of genetic variation across much of eastern Antarctica. In contrast, X. elegans collected from Mawson showed considerable genetic variation from the Vestfolds thalli, differing at 14·2% of nucleotide positions and had an identical ITS region sequence to an isolate from maritime Antarctica 4960 km away. Samples from the Vestfold Hills formed a distinct cluster in a phylogenetic analysis of ITS sequences from a worldwide collection of X. elegans isolates.     

High levels of variation despite genetic fragmentation in populations of the endangered mountain pygmy-possum, Burramys parvus, in alpine Australia

In endangered mammals, levels of genetic variation are often low and this is accompanied by genetic divergence among populations. The mountain pygmy-possum (Burramys parvus) is an endangered marsupial restricted to the alpine region of Victoria and New South Wales, Australia. By scoring variation at eight microsatellite loci, we found that B. parvus populations exhibit high levels of genetic divergence and fall into three distinct groups from the northern, central and southern areas of the distribution of this species, consistent with previous assessments of mitochondrial DNA variation. F(ST) values between populations from these regions ranged from 0.19 to 0.54. Within the central area, there was further genetic fragmentation, and a linear association between genetic and geographical distance. This pattern is likely to reflect limited dispersal across barriers despite the fact that individual B. parvus can move several kilometres. Levels of genetic variation within populations were high with the exception of a southern population where there was evidence of inbreeding. From a conservation perspective, all three areas where B. parvus are found should be considered as separate gene pools; management of populations within these areas needs to take into account the low gene flow between populations, as well as threats posed by roads, resorts and other developments in the alpine region. The low genetic variability and inbreeding in the southern population is of particular concern given the high levels of variability in other B. parvus populations.     

Activity pattern of the moss<Emphasis Type="Italic"> Hennediella heimii</Emphasis> (Hedw.) Zand. in the Dry Valleys,Southern Victoria Land,Antarctica during the mid-austral summer

The activity pattern of the moss Hennediella heimii (Hedw.) Zand. was monitored over a period of 18 days during the austral summer season 2000/2001 at the Canada Flush in Taylor Valley, continental Antarctica. Provided with melt water from the massive Canada Glacier, the moss showed a constant potential photosynthetic activity during the entire measurement period. Permanently hydrated, the moss faced high light levels at surprisingly low moss temperatures, which is commonly supposed a deleterious situation for plants. The electron transport rate response of the moss to photosynthetic photon flux densities was linear at all temperatures and did not show a sign of saturation or photoinhibition. H. heimii seems to be well adapted to its environment and tolerates the ambient conditions without apparent harm. This might be due to the fact that mosses can acclimatise to high light conditions by building up highly effective non-photochemical quenching systems.     

Intracolonial genetic variation in the scleractinian coral Seriatopora hystrix

In recent years, increasing numbers of studies revealed intraorganismal genetic variation, primarily in modular organisms like plants or colonial marine invertebrates. Two underlying mechanisms are distinguished: Mosaicism is caused by somatic mutation, whereas chimerism originates from allogeneic fusion. We investigated the occurrence of intracolonial genetic variation at microsatellite loci in five natural populations of the scleractinian coral Seriatopora hystrix on the Great Barrier Reef. This coral is a widely distributed, brooding species that is at present a target of intensive population genetic research on reproduction and dispersal patterns. From each of 155 S. hystrix colonies, either two or three samples were genotyped at five or six loci. Twenty-seven (~17%) genetically heterogeneous colonies were found. Statistical analyses indicated the occurrence of both mosaicism and chimerism. In most cases, intracolonial variation was found only at a single allele. Our analyses suggest that somatic mutations present a major source of genetic heterogeneity within a single colony. Moreover, we observed large, apparently stable chimeric colonies that harbored clearly distinct genotypes and contrast these findings with the patterns typically observed in laboratory-based experiments. We discuss the error that mosaicism and chimerism introduce into population genetic analyses.     

Genetic variation and population structure in Korean endemic species: III.Hosta minor (Liliaceae)

Hosta minor, an insect-pollinated and rhizomatous herbaceous perennial, occurs in eastern and southern Korean Peninsula. AlthoughH. minor is a Korean endemic species and most populations of the species are scattered, the species maintains considerably high levels of genetic variation within the species, with a moderate level of variation (14%) found among populations. Nineteen of the 29 putative loci resolved (66%) were polymorphic within the species, the mean number of alleles per locus was 2.10 across all populations and averaged 1.68 within populations. In addition, genetic diversity was a considerably higher (for species and population level, mean estimates of genetic diversity were 0.275 and 0.230, respectively) than the average for other long-lived herbaceous perennials. Indirect estimate of the number of migrants per generation (Nm=1.03, calculated from mean G_ST) was moderate. Factors contributing to the high levels of genetic diversity found within populations ofH. minor include population maintenance via sexual and asexual modes of reproduction, primarily outcrossing breeding system, long generation time, probable ancient polyploid origin of the species, and moderate levels of seed dispersal by wind. Human disturbance in South Korea such as road and apartment constructions appears to be the major threat to this genetically diverse species.     

Extended ecophysiological analysis of Gomphiocephalus hodgsoni (Collembola): flexibility in life history strategy and population response

The springtail Gomphiocephalus hodgsoni (Arthropoda: Collembola) has been the focus of extensive ecophysiological and molecular genetic work and is now arguably the most well-studied of the continental Antarctic springtails. Here, we further the ecophysiological catalogue of this species. First, we provide experimental data on G. hodgsoni from one summer season at Cape Bird (Ross Sea Region) examining dispersal ability and desiccation tolerance. Next, we expand an existing metabolic rate dataset that encompasses individual metabolic rate measurements across both temporal and spatial scales in southern Victoria Land, adding an additional season of metabolic rate measurements taken at a cooler, drier continental location (Garwood Valley). Our data show that some G. hodgsoni individuals can survive at least ten days of suspension on the surface of both fresh and sea water. This, coupled with the presence of G. hodgsoni specimens in air and pitfall traps suggests that dispersal over local scales (i.e. metres) is possible for this species. Our metabolic data show that different populations within the same Antarctic region have different average metabolic rates at both temporal and spatial scales, indicating that distinct populations may respond differently to environmental variables. We suggest that G. hodgsoni maintains a flexible life history strategy that allows its ecophysiological response(s) to be dependent on local environmental conditions. Accordingly, there may be no ‘typical’ response to environmental changes—a factor that should be considered in both future ecophysiological work and conservation approaches.     

Life cycle and social behavior in a heathland population of the allodapine bee,Exoneura bicolor (Hymenoptera: Apidae)

Summary Previous studies of the allodapine beeExoneura bicolor have utilised a predominantly social population from tall montane forests. In this report we examine aspects of the sociality and biology of a population from subcoastal heathland in western Victoria, Australia. Entire colonies, nesting inXanthorrhoea minor, were collected at monthly intervals over 12 months between February 1989 and January 1990. In addition, three collections fromMelaleuca squarrosa were made over three consecutive winter months. The heathland population differs from the montane population in several aspects associated with sociality: (i) it shows lower levels of co-occupancy in both newly founded and re-used nests; (ii) foundress dispersal occurs over a larger proportion of the year; and (iii) there may be a partical second brood produced in late summer, during and after adult eclosion of the first brood. The occurrence of a partial second brood gives rise to opportunities for sib-rearing and eusociality. Colony sizes tend to be larger inM. squarrosa thanX. minor, but still smaller than colonies from the montane population. Egg-laying commences several weeks earlier in multifemale colonies than in single female colonies, before spring dispersal begins. It appears that multifemale colonies are more successful at preventing brood loss than single females and that the mean number of brood per female is larger in multifemale colonies than in single female colonies. These two populations, which display differences in several life history traits, provide an ideal system for studying the mechanisms maintaining social behavior.     

High levels of genetic variability in the moss Ceratodon purpureus from continental Antarctica, subantarctic Heard and Macquarie Islands, and Australasia

The random amplified polymorphic DNA (RAPD) technique, and DNA sequencing of the conserved nuclear ribosomal DNA internal transcribed spacer region (ITS1-5.8S-ITS2), have been used to assess levels of genetic diversity in the moss Ceratodon purpureus from several locations in Australasia, subantarctic Heard and Macquarie Islands, and continental Antarctica. Populations from Heard and Macquarie Islands and from Antarctica maintain high levels of genetic variation. Both within- and among-colony variation were observed at these locations. DNA sequence analysis showed that samples from the Ross Sea region of Antarctica were most closely related to colonies from Casey and Macquarie Island, and that one colony from Heard Island was most closely related to one from Europe. DNA sequence data separated two Australian populations from the Antarctic and subantarctic group on a dendrogram. Detailed RAPD analysis of a single colony from continental Antarctica demonstrated that mutation probably causes the high variability observed in this moss. DNA sequencing and RAPD analysis are complementary techniques for genetic investigation of Antarctic moss populations.Jenny Ninham was an integral part of this research team for several years. Unfortunately she did not live to see these results published.     

Drought survival strategies,dispersal potential and persistence of invertebrate species in an intermittent stream landscape

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Significant patterns of population genetic structure and limited gene flow in a threatened macropodid marsupial despite continuous habitat in southeast Queensland, Australia

Many endangered species worldwide are found in remnant populations, often within fragmented landscapes. However, when possible, an understanding of the natural extent of population structure and dispersal behaviour of threatened species would assist in their conservation and management. The brush-tailed rock-wallaby (Petrogale penicillata), a once abundant and widespread rock-wallaby species across southeastern Australia, has become nearly extinct across much of the southern part of its range. However, the northern part of the species’ range still sustains many small colonies closely distributed across suitable habitat, providing a rare opportunity to investigate the natural population dynamics of a listed threatened species. We used 12 microsatellite markers to investigate genetic diversity, population structure and gene flow among brush-tailed rock-wallaby colonies within and among two valley regions with continuous habitat in southeast Queensland. We documented high and significant levels of population genetic structure between rock-wallaby colonies embedded in continuous escarpment habitat and forest. We found a strong and significant pattern of isolation-by-distance among colonies indicating restricted gene flow over a small geographic scale ( <10 km) and conclude that gene flow is more likely limited by intrinsic factors rather than environmental factors. In addition, we provide evidence that genetic diversity was significantly lower in colonies located in a more isolated valley region compared to colonies located in a valley region surrounded by continuous habitat. These findings shed light on the processes that have resulted in the endangered status of rock-wallaby species in Australia and they have strong implications for the conservation and management of both the remaining ‘connected’8 brush-tailed rock-wallaby colonies in the northern parts of the species’8 range and the remnant endangered populations in the south.