Who eats whom? DNA techniques uncover the secrets of food webs

Novel DNA-based techniques provide entirely new information on bats, pollinators, fungi and other species that have been difficult to observe previously. This is revolutionising our understanding of the world, as most of the species on this planet are small and difficult to identify, with previously unknown roles in the ecosystem.

In recent years, research focused on interaction between species and on entire biological communities has increasingly come to rely on techniques based on DNA. Indeed, the advances in DNA techniques and the details they reveal about biological communities are the focus of the recently published special issue of the scientific journal Molecular Ecology, including a significant contribution by Finnish researchers.

New DNA techniques help determine the formation of complex food webs through interaction between individual species: who eats whom, which species decompose edible mushrooms and which pollinators visit what plants. Many such interactions were undetectable using older techniques.

Bats are a prime example of secretive species that are difficult to study. For a long time, the diet of these nocturnal insectivores has been guesswork. Now, prey species can be identified by investigating bat faeces found in their daytime hideouts using DNA methods.

“These days, DNA residue from prey is easily sequenced from bat faeces, helping us understand how animals as different as bats and insectivorous birds live on practically identical food,” says Eero Vesterinen, postdoctoral researcher at the University of Turku. 

Three of the articles included in the newly-published special issue of Molecular Ecology have been written by a research group Spatial food web ecology led by Professor Tomas Roslin from the University of Helsinki. They describe which insects pollinate mountain avens across the Arctic, how climate change affects wolf spiders, the invertebrate apex predators of the Arctic region, as well as which insects inhabit our most common edible mushrooms.

“We put whole mushrooms into a blender and extracted the DNA of various insect species from the mushroom shake. This enabled us to study how the age and structure of forests affect the insect species found in mushrooms. In addition, we are able to identify the insects that compete with mushroom pickers for the best hauls,” explains Janne Koskinen, a doctoral student at the University of Eastern Finland.

Grant-funded researcher Mikko Tiusanen from the University of Helsinki utilised DNA techniques when identifying mountain avens' pollinators caught with artificial flowers made out of flypaper.

“We managed to catch a total of 30,000 pollinators from across the northern hemisphere. Analysing such an extensive dataset without DNA techniques is practically impossible, or requires no less than years of work by dozens of specialists.”

Knowing how species and their mutual interaction react to environmental changes, such as global warming, is of utmost importance in a changing world.

“Wolf spiders are the true masters of the Arctic, representing an existential threat to all smaller organisms. We investigated their nutrition on the fell slopes of north-eastern Greenland, finding that the spiders prefer certain species of flies regardless of climate conditions. However, climate does have an effect on how many flies there are to catch,” Roslin explains.

Original articles : Molecular Ecology special issue: Species, interactions, ecological networks and community dynamics