Plant Life at Extremes – Evolution for Survival in Antarctica

A project undertaken at the Genomic Interactions Group, Research School of Biological Sciences, Australian National University, Canberra, and supervised by M Skotnicki

Antarctica is the coldest, driest, windiest and most inaccessible continent on earth, with inherent difficulties for scientific research which make otherwise practical experiments impossible. Only about 2% of continental Antarctica is ice-free, with a few moss species constituting the dominant but very sparse terrestrial vegetation. Despite these difficulties, Antarctic terrestrial vegetation offers exceptional opportunities for gaining novel insights into both the mechanisms of plant survival under extreme conditions, and plant genetic evolution, especially in response to increased UV irradiation with climate change. These plants also provide a glimpse of the wide scope of adaptation and evolution in pristine habitats once thought to be incompatible with life, but now of increasing interest as a unique tourist destination in need of careful conservation and management.

This project aims to use techniques of molecular genetics to investigate the biodiversity and evolution of plants for survival in the extremely inhospitable polar desert ecosystem of Antarctica. These mosses live “on the edge”, and can provide an early indication of how plant populations will evolve in response to climate change, with measurable warming already occurring and the ozone hole exposing Antarctic plants to significantly higher levels of UV irradiation.

Research into Antarctic biodiversity, including this genetic research, has been identified by both Australian and International Antarctic Science Advisory Committees as a high priority. This project contributes significantly to Australia’s role in international efforts to study the evolution of organisms in Antarctica, and the effects of climate change on these processes, as well as conservation of the pristine environment and ecosystems of Antarctica.

The practical objectives of this project are:

  1. to investigate the extent of genetic mutation which is occurring in living moss plants (up to 100 years old) in Antarctica.
  2. to relate the results obtained to growth rates, and to the increasing level of UV exposure.
  3. to provide DNA sequence data useful for  taxonomic purposes, as many Antarctic mosses show plasticity of their morphology due to the extraordinary environment, making identification difficult or impossible.
  4. to provide information useful for developing sound and practical conservation strategies for Antarctica, both for the Australian Antarctic Territory and internationally.

Recently, by screening more than 100 shoots from single colonies of the moss Ceratodon purpureus from the southernmost location where we have found this moss (southern Victoria Land, at 750S), we have clearly demonstrated that (a) significant levels of within-colony variation occur at the DNA level, (b) physically closer shoots are more closely related genetically, (c) occasional variation occurs between two joined branches of the same shoot, (d) occasional variation can occur along the length of old shoots, and (e) levels of genetic variation appear higher than within Australian colonies. Thus it appears that mutation plays a major role as a source of variation in Antarctic mosses, enabling evolution and survival in the climatic extremes.

Some potential genes for mutation analysis within single moss shoots have been identified, and preliminary experiments have been done with Antarctic mosses to amplify and sequence genes from old and young sections of individual shoots. Gene sequencing for multiple specimens of several moss species from different locations in Antarctica has confirmed and extended the results obtained with simpler techniques, showing that genetic diversity is extensive within Antarctic mosses.

For analysis of rates of mutation, it is essential to know the growth rate of mosses in Antarctica, so that genetic changes along the length of a shoot can be correlated with age of those segments of the shoot. Calculations of growth rates of three moss species near Casey Station in the Australian Antarctic Territory is nearing completion; this will be the first documented study of Antarctic moss growth rates, with measurements taken over 20 years. Analysis of the data has shown that growth rates are around 0.1 – 0.5 mm per year.

The ribosomal ITS region has been sequenced from the eight dominant species found in Victoria Land, with samples from a variety of sites along the Victoria Land coast including Edmonson Point, Mt. Melbourne, Granite Harbour, Taylor Valley, Ross Island and Mt. Erebus. The results have clearly shown that each species can be readily identified taxonomically, and ITS sequencing is likely to become a most useful addition to the taxonomic methods for these mosses. The method is already proving useful for identification of unknown mosses from Antarctica.

In addition, we have shown that Antarctic moss populations do show genetic differences (cryptic speciation) even within this highly conserved region of the genome. Comparison (using both DNA sequencing and RAPD technology) of continental Antarctic populations with those from subantarctic Heard and Macquarie Islands, and with Australasian populations, has revealed distinct genetic clustering of populations as well as preliminary indications of dispersal between locations.

Publications
Skotnicki, M.L., Bargagli, R. and Ninham, J.A. (2002) Genetic diversity in the moss Pohlia nutans on geothermal ground of Mount Rittmann, Victoria Land, Antarctica. Polar Biology 25: 771-777

Bargagli, R., M. L. Skotnicki, L. Marri, M. Pepi, A. Mackenzie & C. Agnorelli (2004). New record of moss and thermophilic bacteria species and physico-chemical properties of geothermal soils on the northwest slope of Mt. Melbourne (Antarctica) Polar Biology 27: 423 - 431

Skotnicki, M. L., A. M. Mackenzie, J. A. Ninham & P.M. Selkirk (2004). High levels of genetic variability in the moss Ceratodon purpureus from continental Antarctica, subantarctic Heard and Macquarie Islands, and Australasia. Polar Biology 01 July, 2004 Online First

Skotnicki, M.L., A. M. Mackenzie & P.M. Selkirk (2004). Mosses Surviving on the Edge: Origins, Genetic Diversity and Mutation in Antarctica. Annals of the Missouri Botanical Gardens (in press).

Skotnicki, M. L., A. M. Mackenzie, M. A. Clements & P.M. Selkirk. Genetic characterisation of the 18S - 26S nuclear ribosomal DNA internal transcribed spacers (ITS) in nine Antarctic moss species. Antarctic Science (submitted).

Selkirk, P. M. & M. L. Skotnicki. How fast do mosses grow in Antarctica? Polar Biology (in preparation).

Unusually lush growth of the moss Bryum argenteum in a very protected site between boulders in a meltwater channel, at Granite Harbour in southern Victoria Land, Antarctica. Note red penknife in the centre of the colony for scale. This colony is probably hundreds of years old, or more, and has genetic mutation occurring within the colony as detected by molecular methods (RAPDs)

Growth of the moss Bryum argenteum in the Dry Valleys, southern Victoria Land, Antarctica, with penknife for scale. Small moss colonies such as this are typical, clinging to life on the edge where a rock provides just sufficient protection from the harsh environment, and a small amount of water is provided by meltwater runoff from a snowpatch or glacier.

Long shoots of the moss Ceratodon purpureus from Granite Harbour, southern Victoria land, Antarctica. Because the growth rate is probably less than 1 mm per year, these shoots represent up to 100 years' growth. DNA can be extracted and analysed from sections along the length of single shoots, enabling analysis of mutation with time.

Agarose gel, with each well containing amplified DNA from individual shoots within a single colony (size markers on right). One additional band in one sample on the gel can be seen; this represents a mutation within that shoot

Field camp on Heard Island

Royal penguins amongst the plant life on subantarctic Macquarie Island. In another project, we have detected the first plant virus on this remote island, in the "Macquarie Island cabbage" with large leaves shown in this photo. We are also studying the mosses from Macquarie Island to understand the biodiversity and dispersal of mosses to this recent and very isolated island

 

Subantarctic Heard Island, Australia's only active volcano and highest mountain, in the sunset. We are studying the plant biodiversity and dispersal of mosses on this remote glaciated island, using molecular techniques to assist moss taxonomy