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.