DNA analyses map arctic food webs
Gene sequences are now used to describe the interactions between plants and animals in the arctic ecosystem and the role played by climate change.
“Interactions between species are so much simpler to study in the Arctic than in the rest of world. By way of example, we found almost 30,000 different insects in a tropical rain forest of only 6,000 ha, while here in the tundra in north-east Greenland, there are only some 300 different species,” says associate professor Tomas Roslin from the University of Helsinki, Finland.
Tomas Roslin sets up traps and takes samples at the Zackenberg Research Station in north-east Greenland. He has been here every summer since 2009 to gather all species within the area. By describing the same gene for all species, you may use its sequence as an unambiguous and easily readable character to identify any species.
Scientist have come a very long way in their mapping. The gene sequences of all birds and vertebrates have now been established, and the gene sequences of nearly 90% of the area’s plants and insects have been completed as well.
“Gene sequences can be thought of as the bar codes on products in any grocery store, and we have now obtained an incredible reference library of almost all species in the area. In the future this will allow us to rapidly describe the species present in any sampling. Furthermore, we can easily recognize parts of animals and plants – also when they have been eaten by another animal,” says Tomas Roslin.
Such individual species are well worth knowing, because, when setting traps to catch insects, the scientists may easily obtain more than 200 different species from a single trap – even when sampling is undertaken in one of the world’s most simple ecosystems exhibiting the lowest number of species.
So far, multiple hours behind the microscope have been required to assign each individual to the species level, and often the scientists have had to forward samples around the globe to various experts for them to identify and name difficult species. Soon the same work can be done by grinding all the insects of a sample and forwarding some of the ‘soup’ for DNA analysis. The microscope has been exchanged with a fast computer that compares the results of the DNA analysis with the scientists’ database and creates a list of the species present in the sample.
Fingerprints are stored in the food web
The analyses may be used for more than just recording the presence of various species. The scientists have also used the gene sequences to describe the relationships between the different components of the arctic terrestrial food webs and can in this way answer the question: ‘Who eats who’?
Sequences within the selected gene are unique for each individual species, and this ‘fingerprint’ can be traced in the food webs. If you, for instance, analyse the excrements from a bird, you can, based on the DNA content, determine which insects the bird has fed on.
In the same way, the scientists hope to determine the plants fed upon by musk oxen at various times of the year by analysing fresh excrements from the animals. And what is truly unique is that a small sample of an adult insect still contains traces of the prey that it ate at the larval stage.
One of the world’s longest time series
“Zackenberg Research Station in north-east Greenland is completely unique. It provides us with the logistics necessary for undertaking comprehensive samplings in the high-Arctic area. At the same time, Aarhus University has gathered, measured and described animals and plants since 1996 following detailed guidelines. This gives us one of the world’s longest, unbroken and most extensive time series of arctic data,” explains Tomas Roslin.
The gathered samples are kept in a store room at the Natural History Museum in Aarhus. Now, Tomas Roslin and an international group of collaboration partners will analyse small quantities of the samples and in this way undertake an accurate determination of which species have been present during the almost 20-year long sampling period. This will enable the scientists to follow the changes in the composition of species occurring in the high-Arctic area back in time and, thus, evaluate how the climate changes impact the terrestrial ecosystem in the Arctic.
Tomas Roslin, Department of Agricultural Sciences, University of Helsinki: Tomas.Roslin@Helsinki.fi