Freshwater connectivity can transport environmental DNA through the landscape

A new paper published in the journal Proceedings of the Royal Society B used environmental DNA (eDNA) metabarcoding to analyze fish and zooplankton communities. The study found that the movement of water between freshwater bodies, or freshwater connectivity, can transport eDNA. This highlights the potential of eDNA to provide a comprehensive view of freshwater biodiversity.

Aquatic ecosystems are connected by waterways, which allow fish, plants, and other organisms to move from one place to another. This connectivity is important for the resilience of aquatic populations, but it can also make it difficult to track the DNA of these organisms.

The study, led by Dr Joanne Littlefair, a lecturer in biological sciences at Queen Mary University of London, looked at three lake networks containing 21 lakes in Canada's Boreal Forest at IISD Experimental Lakes Area. The researchers found that within-lake eDNA generally reflected the habitat preferences of the species, but that some eDNA was also transported into downstream lakes. Lakes with a higher degree of connectivity had more eDNA detections that could not be explained by conventional monitoring techniques.

The findings have implications for the use of eDNA to monitor biodiversity in freshwater ecosystems. eDNA is a promising tool for biodiversity monitoring, but data must be interpreted in light of connectivity in the landscape.

"eDNA can be used to detect the presence of species that are not easily monitored using conventional methods, including invasive species, or for monitoring the presence of rare or endangered species," said Dr Littlefair." "Our study showed that eDNA surveys can be carefully designed to consider the connectivity of the freshwater system being studied. In systems with high levels of connectivity, it is important to collect samples from multiple locations, which will allow us to build a complete picture of the biodiversity present."

The study also highlights the need for more research on the factors, such as effects of water movement, influencing the spatial resolution of eDNA detection. For example, if the water in an ecosystem is moving quickly, then it may be necessary to collect more samples to increase the chances of detecting eDNA. This research will help to improve scientists' understanding of how eDNA can be used to monitor and conserve aquatic biodiversity.

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Solving Everest's wildlife mysteries with eDNA

A team of scientists led by the Wildlife Conservation Society (WCS) and Appalachian State University used environmental DNA (eDNA) to document the breadth of high-alpine biodiversity present on Earth's highest mountain, 29,032-foot Mt. Everest (8,849 m).

Describing their findings in the journal iScience, the team collected eDNA from water samples over a four-week period in ten ponds and streams between 14,763 feet (4,500 meters) and 18,044 feet (5,500 meters). The sites included areas of the alpine zone that exist above the tree line and contain an array of flowering plants and shrub species, along with the aeolian zone that reaches beyond the range of flowering plants and shrubs at the uppermost reaches of the biosphere. From just 20 liters of water, they identified organisms belonging to 187 taxonomic orders, which corresponds to 16.3 percent, or one sixth, of the total known orders across the tree of life -- a family tree of Earth's biodiversity.

eDNA searches for trace amounts of genetic material left behind by organisms and wildlife and offers a more accessible, rapid, and comprehensive approach to increasing survey capacity for assessing biodiversity in aquatic environments. Samples are collected using a sealed cartridge containing a filter that captures genetic material that is later analyzed at a lab using DNA metabarcoding and other sequencing methodologies. WCS has been using eDNA for detection of rare and threatened species from humpback whales to Swinhoe's softshell turtle, one of the rarest species on the planet.

Although the Everest study focused on identification at the order level, the team was able to identify many organisms to the genus or species level.

For example, the team identified both rotifers and tardigrades, two tiny animal organisms that are known to occur in the harshest and most extreme environments and are considered to be among the most resilient animals known on Earth. In addition, they identified Tibetan snow cock, which are found in Sagarmatha National Park, and were surprised to find species such as domestic dog and chicken, representing how human activities are influencing the landscape.

They also identified pine trees, which only are found far downhill from where they sampled, demonstrating how wind-blown pollen can make its way high up into these watersheds. Another organism they identified from several sites were mayflies, which are known indicator species for environmental change.

The eDNA inventory will aid future high-Himalayan biomonitoring and retrospective molecular studies to assess changes over time as climate-driven warming, glacial melt, and human-caused influences reshape this rapidly transforming world-renowned ecosystem.

Said Dr. Tracie Seimon of WCS's Zoological Health Program, co-lead of the Everest biology field team and lead of the study: "High-alpine and aeolian environments, which have often been thought of as barren and mostly devoid of life, in fact have abundant biodiversity. High mountain environments including Mount Everest should be recognized as a target for sustained long-term biodiversity monitoring of high-alpine taxa to complement bioclimatic monitoring and climate change impact assessments."

Said Dr. Marisa Lim of the Wildlife Conservation Society: "We went in search for life on the roof of the world. This is what we found. However, the story does not end here. There is more to be discovered and we hope our findings help to inform future exploration."

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