Stephen McKechnie, Program Leader
"We've generated cold tolerant strains by selection in the laboratory and found three or four new genes that changed as a consequence."
|
|
Climate change and global warming are challenging our flora
and fauna, as well as agricultural crops and stocks. Climate change will impose extended periods
of high temperature, desiccation stress, and the depletion of food and nutrients
upon plant and animal populations. Some species are likely to become extinct,
others may adapt. The Climatic Stress Program
is concerned with understanding how organisms adapt and change genetically in
response to such varying and extreme physical stresses.
Like the Program on Chemical Stress, our research on climatic
stress centres on the genus Drosophila
and in particular on Drosophila
melanogaster, a stress resistant and genetically well characterised species. A major objective of the Climatic Stress
Program is to understand the physiological and genetic basis of the large
differences in resistance to desiccation, heat and cold that occur between this
cosmopolitan generalist species and several of its look-alike ‘cousin’
specialist species, often rainforest species, which are sensitive to
desiccation and to the extremes of heat and cold. In addition, D. melanogaster displays marked and heritable differentiation among
strains collected from different climatic regions, as often occurs with other
wide-ranging plant or animal species. A
prime focus for many of our studies has been dissecting the clinal variation in
heat and cold tolerance that occurs along a 3,000km latitudinal transect in
eastern Australia.
We are also
investigating the effects on climate change on Australian alpine regions which
are limited in distribution and highly threatened. This involves regular
detailed monitoring of plant populations and their characteristics, monitoring environmental
changes, and assessing the effects of simulated warming in experimental plots.
These data will allow us to predict how future climate change will
affect the ecology of this system and apply results to long-term management
strategies for the Alpine National Park.
Highlights of the work in recent years include:
Identification of two rainforest-restricted species, D. birchii and D. bunnanda, that have very low levels of adaptive variation for
desiccation resistance, despite harbouring large amounts of genetic variation
for morphological traits and a range of genetic markers. This result rings alarm bells because several
other related species that are not so specialised in their habitat requirements
are able to respond to selection and can be made to ‘evolve’ in the laboratory
to be desiccation resistant. We are working
to find the essential differences in the evolutionary processes and genes
involved in adaptation to climatic stress in these species, to see if these
same limits to adaptation occur for other specialist species and for other
stress resistance traits.
Genetic changes in populations are likely to serve as
biomarkers for increasingly warmer and drier conditions. Geographical clines in the frequency of
genetic markers provide some of the best evidence of climatic selection. In the wide-ranging Drosophila melanogaster two latitudinal clines, in the alcohol
dehydrogenase gene and a chromosomal marker, have shifted over twenty years
along the eastern coast of Australia. Thus the present day genetic constitution of
the species around, say, Sydney is now the same as it was 20 years ago further
north in Coffs Harbour, and so on along the entire eastern coastline. Populations are adapting to climate change –
habitats are becoming warmer and drier.
Since adaptive changes in climatically influenced genetic markers are
likely to precede local population extinction when harsh environments encroach,
adaptive genetic markers such as these provide future monitoring tools for the
early detection of the impact of climate change.
Working with several alpine plant species we have
established that species with
similar altitudinal ranges are likely to respond differently to climate change. We have examined the potential response of two dominant
species of Australian alpine plants (Poa
hiemata, Craspedia lamicola) to
adapt to future global warming. Soft Snow-grass (Poa
hiemata) displays
high levels of morphological variation; grasses at high altitude sites having
shorter leaf lengths and larger circumferences than those at lower sites.
Variation in morphology is partly genetic and partly environmentally driven and
plants are locally adapted to their home environment. Soft Snow-grass has
the potential to respond to global warming that includes an adaptive plastic
response as well as genetic shifts. In comparison, field studies with Shiny-leaf
Billy-button (Craspedia
lamicola) show lower levels of morphological variation and
populations are not locally adapted to various microclimates. In this species variation
in morphology is predominantly environmentally driven.
Field studies of Drosophila
that are subjected to natural climatic stresses are revealing fascinating
insights into traits and genes that are important for populations to
persist. Monitoring of egg production
over the winter period in cool temperate regions, and as spring temperatures
increase, indicates that strains from temperate regions are more productive
than those from the tropics. Further, particular
genetic types, those found at high frequencies in temperate populations, are
superior in this regard. The genes contributing
to successful over-wintering are not predominant in tropical populations. Also, we find that the field study of
resource-finding abilities under particularly hot or cold conditions is revealing
ecologically important information about climatic selection in nature. Thus,
field release/re-capture experiments using D.
melanogaster have confirmed that populations selected in the laboratory for
heat resistance perform better – they are captured in higher numbers – when
released on hot days. These results
demonstrate that traits we are ‘manipulating’ in the laboratory are meaningful
ecologically. These field release/re-capture
experiments at different temperatures are also providing insight into how the
environment selects for wing and body size (traits that vary across climatic
gradients). They also reveal that variation in particular genes influences the
chances of being recaptured, differentially under hot or cold conditions. Field data such as these are providing detailed
understanding of how adaptation to climatic change occurs at both the
phenotypic and molecular levels.
|
Our current projects are listed below:
