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HIDDEN SECRETS OF A MOLECULE: WHAT CAN DNA TELL US ABOUT BIOLGICAL INVASIONS?

Plant invasions pose serious threats to natural and agricultural ecosystems and the services they deliver. The successful management of invasive plants is thus paramount to ensure the sustainability of these services and, more importantly, to conserve native biodiversity. South Africa is currently the “new” home to many introduced and invasive species. Many of these have been introduced intentionally and have become a part of our daily lives. For instance, Acacia cyclops, better known locally as rooikrans, was introduced to stabilize dune movement in the Western Cape Province but is now a major weed. Not only is rooikrans threatening the very sensitive fynbos ecosystem by forming dense monotypic stands, it also influences the services this ecosystem delivers such as water supply.

Management of weeds can be broadly categorized under three types: prevention, eradication and control. Prevention makes sure that no new foreign species are introduced, while eradication aims to remove all individuals of an already-established species. Control aims to reduce population sizes and/or to contain existing populations by reducing their spread into the environment. Unfortunately most management plans are only implemented after weedy species have spread over substantial areas in their new ranges, often making eradication impossible. Indeed, there has not been a single successful eradication of alien plant species on the African continent to date. It is not surprising therefore that most management strategies aim at reducing the impacts of already-established species.

Control strategies can be of chemical, mechanical or biological nature. Chemical control is often unfeasible as widely occurring weed populations would require extensive applications, with potentially damaging effects on native biota and contamination of resources such as ground water. Mechanical control often requires vast resources (funding and manpower) to ensure success. Biological control is a practice that makes use of the natural enemies of weeds from their native ranges. This approach exploits the native biota such as pathogens and/or herbivores that keeps weedy populations in check in their native environments. The idea is that these natural enemies will have the same negative impacts on their host in the introduced range. This approach requires substnatial financial investment but, following the release of successful enemies, is the most economical approach to weed management. The introduction of these natural enemies requires rigorous testing to ensure that they will indeed be effective against particular invaders and at the same time will not have any undesired impacts on non-target species, especially native species.

With the ever increasing growth in international trade and commerce it is apparent that species will be introduced at an increasing rate globally. It is thus important to utilize the most time and cost efficient approaches to aid in management decisions, prevention and risk assessment. One such approach relies on molecular biology, a fairly new field in studying invasive species and their effective management. Since its inception, DNA technology has expanded quickly, offering a unique approach to better understand invasive species and their effective management. These applications can be straight forward such as using DNA barcodes to quickly and reliably indentify invasive species or more sophisticated such as detecting hybridization, dispersal patterns etc. Dr. Jaco Le Roux from the CIB recently published a popular article that reviews some of these uses of molecular genetic approaches in invasive species management [Le Roux, JJ (2008) What can genes tell us about invasive species? Quest, 4, 31-37.]. Follow the link below to download a pdf version of this paper and find out more about this emerging and fascinating field of research aimed at reducing the impacts of biological invasions.

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