Water flea evolution tells a cautionary tale of lake pollution
EU-funded researchers studied genomic changes in water fleas for signs of evolutionary adaptation linked to human activities, such as phosphorous contamination in lakes. The results shed light on how species respond to environmental changes, and could feed into measures to protect biodiversity and ecosystems.
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Ecosystems are sensitive to environmental changes. The slightest change in temperature or local environmental conditions can alter fragile organisms. Yet surprisingly little is known about how man-made, or anthropogenic, environmental changes affect the way organisms evolve and adapt to modified ecosystems. To fill this gap, the EU-funded project ADAPT-ENVGENOME explored how local species adapt over time to human influences.
“We wanted to focus on observed evolutionary changes possibly resulting from something called ‘cultural eutrophication’, or nutrient enrichment of freshwater systems, in particular connected to phosphorus use,” says Joaquin Muñoz of the Donana Biological Station (EBD-CSIC), part of the Spanish Council for Scientific Research (Consejo Superior de Investigaciones Científicas) and coordinator of the project.
Phosphorus and nitrogen are widely applied as fertiliser on farms, which can enter streams, rivers and lakes, through run-off, and lead to eutrophication. The over-abundance of nutrients can cause excessive plant growth and decomposition, removing oxygen from the water, and eventually leading to the death of fish and other animal life.
The project provided evidence that micro-evolutionary change could be linked to varying eutrophication levels from phosphorous contamination, indicating that genetic features are helping generations of water fleas to adapt to varying nutrient levels in the lakes over time.
These findings, which are being documented in a forthcoming book, could have a major impact on water pollution, conservation and other ecosystem concerns such as invasive species being taken into consideration for ecosystem management.
“Overall, the results of this project should shed light on local adaptation at both the population and genomic level to environmental changes, particularly phosphorus contamination in freshwater lakes,” says the research team.
Tale of the fleas
Specifically, the project looked at genomic and physiological changes in the water flea, Daphnia pulicaria. This tiny water-born crustacean is an ideal subject for studying not just individual changes over time but as a model for wider environmental research, suggests the research team.
Indeed, the water flea has been called a ‘canary in the coal mine’ for ecosystem studies. Observing Daphnia’s changes and growth behaviour gives researchers excellent insight into what is going on in lakes and ponds all over the world, and what role humans are playing in this.
“This multidisciplinary approach is an original way to tackle problems of great evolutionary, ecological, and economic importance,” notes Muñoz, who used his Marie Skłodowska-Curie fellowship grant to collect data and study the freshwater ecosystems and cultural eutrophication histories of five distinctive lakes in the US state of Minnesota.
When water fleas reproduce sexually, their eggs can stay dormant in lake sediment for decades before waking up and developing. This means 20-year-old water flea populations, for example, can be resurrected and compared with modern hatchlings.
This type of research is called ‘resurrection ecology’. The dormant eggs also serve as a DNA cache for hundreds of years. By linking genetic changes over time with environmental changes, researchers can virtually see evolution taking place through the prism of this one organism.
A pool of data
The result is a wealth of data on genetics and genomics information in present-day water flea populations and its relatives dating back centuries. Some of the older data are collected by sampling older layers of lake sediments.
“And ultimately, as outlined in Scientific Reports, we should be able to detect those genes involved in such adaptation and micro-evolution, thanks to next-generation sequencing techniques which effectively hone in on the key markers involved,” says the team.
The project brought Muñoz’s organisation together with experts at the University of Oklahoma (USA), in cooperation with the UO Biological Station (UOBS) and the Oklahoma State University (OSU).