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The Himalayan balsam (Impatiens glandulifera) has succeeded. So has the Chinese mitten crab (Eriocheir sinensis). Both belong to the plant and animal species that travelled thousands of kilometers and settled in new regions throughout the world. They often reached these places – if not through humans, birds, or the wind – by accident and were brought along on ships, trains, planes, or cars moving across continents on travel and trade routes. Researchers have long monitored this “migration”. This phenomenon, known as biological invasion, influences the environment – often to a great extent. They are not only capable of disrupting local communities of species and diversity but also of decisively altering the functioning of entire ecosystems. While the invasion of plants and animals has been widely examined, microorganisms have received little attention. At the University of Potsdam, PD. Dr. Guntram Weithoff and his team will contribute to filling this gap.
Cylindrospermopsis raciborskii is the scientific name for the blue-green alga that Weithoff will mainly focus on in the coming years. It is a tiny cyanobacterium, to be exact, which forms microscopic filaments of approximately 0.3 mm and a diameter of 0.003 mm. The bacterium was first recorded in Brandenburg in the 1990s but actually originates from tropical and subtropical regions.
Weithoff and his colleagues examine how these microorganisms alter lakes. Migratory birds and the wind likely brought them to their new habitats. Meanwhile blue-green algae are at home in many bodies of water in Brandenburg. “This is why we have chosen it as a model organism,” Weithoff says. Due to its increasing occurrence, blue-green alga is not only ecologically relevant but also economically, because some strains can form toxins that may affect drinking water production and the recreational value of lakes.
Biological invasions are considered the main cause of the decreasing diversity of species in nature aside from increasing environmental pollution, climate change, and changing land use. A contradiction? Not at all. Although new species also appear at various places in the world, they often supersede the old, resident species. It is a struggle for survival. “This is what interests us,” Weithoff says.
“Experts estimate that biological invasions in aquatic systems in particular will account for the largest decrease in biodiversity until 2050 and beyond.” It continues to be a dangerous development: The zebra mussel, the rainbow trout, and some species of water fleas, to name just a few, have not only positively influenced their new habitats.
The current project focuses on the role of genetic diversity of the model organism and the resident species for invasion success. Research has shown that invasive species are most successful when many of their genotypes are involved. A high genetic diversity of the resident competitors, on the other hand, hampers the “immigrants” from establishing and disseminating in the new environment. The working group is analyzing if this also applies to blue-green algae and which mechanisms take effect.
They will conduct a series of laboratory experiments with phytoplankton as the resident species. The first have been completed, some others are underway. About ten genotypes from the region are being used, a mere fraction of those that exist worldwide. “Our project partner, Dr. Claudia Wiedner from the Brandenburg University of Technology Cottbus-Senftenberg, has isolated them from different lakes,” Weithoff reports. The strains are often morphologically similar. In collaboration with the Potsdam microbiologist Prof. Elke Dittmann, the team is analyzing how they differ genetically, which is important in explaining and assessing their behavior.
The algae the researchers need for their experiments is preserved in permanent cultures in climate cabinets. It floats in a special nutrient solution that ensures its survival. Apart from water, it primarily consists of nutrient salts – like nitrate, phosphate, and carbonate – as well as various trace minerals.
Laboratory experiments are planned for diverse scenarios: The model organism will be added to either individually, in combination with several strains, or with all genotypes of a previously prepared mixture to determine the ideal conditions for the algae to disseminate. It consists of algae, which typically exists in Brandenburg, as well as rotifer as consumers. There are about 70 variations planned. Which strain succeeds in which mixture and which does not? Are there strains that die when isolated but survive in the “wake” of the others? These are only two questions the researchers want to answer. Another equally interesting question is whether a window of opportunity exists during which an invasion is either facilitated or hampered. Research has also insufficiently explained whether the “consumers” have adjusted to the new potential food source in the bodies of water where the algae have existed for decades.
Weithoff and his team are conducting pure basic research. “You cannot exactly simulate outdoor conditions, so we initially need these standardized laboratory experiments to establish the ongoing mechanism,” he explains. “Parallel field experiments are taking place as part of a master thesis. We will be bringing together both parts later and are anticipating important findings.
The new findings on specific genotypes and genotype combinations are to be available by spring 2016. However, it has already become evident that the invasive success of Cylindrospermopsis raciborskii results from the competition for nutrients – and not from reduced predation.
Biological Invasions in Lakes – Genetic Diversity, Timing, and Local Adaptation is funded by the German Research Association (DFG). The project includes researchers from the Institute of Biochemistry and Biology of the University of Potsdam and the Department of Freshwater Conservation of the Brandenburg University of Technology Cottbus-Senftenberg.
Biodiversity primarily refers to the diversity of all living organisms. It includes species diversity, the variation within a species (genetic diversity), the diversity of habitats, and interaction of organisms (functional diversity).
The loss in biodiversity within the last 100 years has been more immense than ever before. Experts think that it is mainly a result of environmental pollution, intensified agriculture, and climate change. Biological diversity is also being threatened by biological invasions, which usually negatively impact invaded habitats. Biological invasion subsumes the process by which species are introduced, established, and spread into a new region.
PD Dr. Guntram Weithoff studied biology at the Freie Universität Berlin. Since November 1999 he has worked as a research fellow in the working group Ecology and Ecosystem Modelling at the Institute of Biochemistry and Biology of the University of Potsdam.
Institut für Biochemie und Biologie
Text: Petra Görlich
Translation: Susanne Voigt
Online-Editing: Silvana Seppä
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