P. M. Selkirk

Biological invasions in the Antarctic: extent, impacts and implications

Alien microbes, fungi, plants and animals occur on most of the sub‐Antarctic islands and some parts of the Antarctic continent. These have arrived over approximately the last two centuries, coincident with human activity in the region. Introduction routes have varied, but are largely associated with movement of people and cargo in connection with industrial, national scientific program and tourist operations. The large majority of aliens are European in origin. They have both direct and indirect impacts on the functioning of species‐poor Antarctic ecosystems, in particular including substantial loss of local biodiversity and changes to ecosystem processes. With rapid climate change occurring in some parts of Antarctica, elevated numbers of introductions and enhanced success of colonization by aliens are likely, with consequent increases in impacts on ecosystems. Mitigation measures that will substantially reduce the risk of introductions to Antarctica and the sub‐Antarctic must focus on reducing propagule loads on humans, and their food, cargo, and transport vessels.

Genetic diversity, mutagenesis and dispersal of Antarctic mosses – a review of progress with molecular studies

In investigating the extent of genetic diversity in Antarctic mosses the RAPD technique has proven especially useful in demonstrating that these mosses exhibit extensive genetic variation (levels being similar to those in temperate regions), and that within-colony variation is apparently caused not only by immigration and establishment of propagules from elsewhere, but also by mutagenesis. Dispersal of these mosses can also be followed using the RAPD technique; both short-distance dispersal by wind or water (depending on the moss species) and longer distance dispersal by wind across the ice cap has been demonstrated. Relationships with temperate mosses of the same species are being investigated to determine the origins of Antarctic populations. Genetic technology is also facilitating the taxonomic identification of moss specimens which cannot be identified morphologically due to phenotypic plasticity in Antarctica. Together, these genetic studies are starting to provide information of fundamental scientific importance for understanding the evolution, origins and dispersal mechanisms of Antarctic mosses, and their response to climate change.

Dispersal of the moss Campylopus pyriformis on geothermal ground near the summits of Mount Erebus and Mount Melbourne, Victoria Land, Antarctica

Mount Melbourne in northern Victoria Land, Antarctica, is a glaciated 2733 m volcanic cone. The moss Compylopus pyriformis occurs on two small areas of steam-warmed snow-free ground near its summit. This moss species also occurs in temperate regions world-wide, but has not been recorded elsewhere in continental Antarctica. RAPD (Random Amplified Polymorphic DNA) studies of 26 samples of C. pyriformis from two areas of heated ground on Mount Melbourne showed there was genetic diversity within the population. Genetic evidence for dispersal between the two sites, together with some genetic variation within individual colonies, indicates a single colonisation event has probably occurred at this extremely isolated location followed by multiple mutations. A single sample of moss protonema was collected 25 years ago from steam-warmed ground near the summit of another volcano, Mount Erebus (3794 m), on Ross Island some 300 km south of Mount Melbourne. The moss could not be identified based on morphological and reproductive criteria, as all attempts to differentiate it to a recognisable gametophyte were unsuccessful. The RAPD technique has now shown it to be C. pyriformis, and closely related to the population on Mount Melbourne.

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.

Genetic variation in antarctic populations of the moss Sarconeurum glaciale

Abstract 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.

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

Abstract 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.

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

Abstract 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.

DNA sequencing and genetic diversity of the 18S-26S nuclear ribosomal internal transcribed spacers (ITS) in nine Antarctic moss species

We have sequenced the 18S–26S nuclear ribosomal DNA ITS region from the genome of nine different moss species from the Ross Sea region of Antarctica. This relatively quick and simple technique enables these species to be readily distinguished, facilitating their taxonomic identification. Only a single moss shoot is required, and for identification of these bryophytes it is only necessary to determine a few hundred nucleotides of the DNA sequence in a single sequencing reaction. Several previously unidentified Antarctic moss specimens were readily characterized by comparison with ITS sequences of known moss species. The relationships between species and locations previously detected by the RAPD (Random Amplified Polymorphic DNA) technique were confirmed by DNA sequencing, demonstrating that the two techniques can be complementary for molecular analysis of the ecology of mosses in Antarctica.

The first subantarctic plant virus report: Stilbocarpa mosaic bacilliform badnavirus (SMBV) from Macquarie Island

Abstract. We report here the finding of a new plant virus, Stilbocarpa mosaic bacilliform badnavirus (SMBV) in Stilbocarpa polaris (Homb. et Jacq.) Gray on subantarctic Macquarie Island. This is the first vascular plant virus reported from any of the remote subantarctic islands, and represents the southernmost plant virus found anywhere. The virus causes mild to severe yellow mosaic symptoms in the perennial megaherb S. polaris. Virus distribution appears most widespread in the northern third of Macquarie Island, although S. polaris occurs around the whole island. DNA sequencing of a conserved part of the virus genome showed it is most closely related to badnaviruses of temperate and tropical plants, which are mainly transmitted by mealybugs (Hemiptera: Coccoidea). No mealybugs have been found on Macquarie Island, where the vector may be an aphid (Hemiptera: Aphidoidea) or thrip (Thysanoptera). We discuss possible origins, dispersal and evolution of this plant virus on isolated Macquarie Island.

Genetic diversity in the moss Hennediella heimii in Miers Valley, southern Victoria Land, Antarctica

Abstract The moss Hennediella heimii constitutes a significant proportion of the terrestrial flora of East Antarctica, especially in the McMurdo Dry Valleys region of southern Victoria Land. This is the first investigation of the extent of genetic variation within a population of H. heimii. Random Amplified Polymorphic DNA has been used to study both genetic diversity and dispersal of this moss in Miers Valley, southern Victoria Land. The results showed that genetic variation does occur in H. heimii (possibly due to increased exposure to UV-B irradiation), even between shoots within single colonies, and that colonies collected from three transects along meltstreams within the valley constitute a single large population. However, comparison with samples of the same species from nearby valleys and sites up to 500 km distant showed that the Miers Valley population is distinct from these other populations. The results also indicate that wind plays a major role in dispersal of H. heimii in this region of Antarctica.