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DNA traces from cow dung reveal insect diversity

Researchers at the Department of Biology at Aarhus University and the Natural History Museum in Aarhus have now shown that cow pads contain DNA from the entire community of insects inhabiting the dung.

2020.12.10 | Peter F. Gammelby og Philip Francis Thomsen

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Newly laid cow dung from Mols Bjerge, where samples for this study were collected. The dung is already colonized by insects, which can be seen from the holes in the surface. Photo: Philip Francis Thomsen.

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A myriad of dung beetles (Aphodius spp.) on cow dung, which were some of the species found in the study. Dung beetles live in and feed on the dung. Photo: Morten DD Hansen.

It is no longer necessary to rummage through entire cow pads to find out which animals live in – and off - the dung. One can simply take a small sample and analyze all the DNA traces in it. From cow pads found in dry grassland, meadow and forest on the grounds of the Mols Laboratory in the Mols Hills near Aarhus, scientists from Department of Biology at Aarhus University and the Natural History Museum in Aarhus have detected DNA from at least 54 species of arthropods, including beetles, flies and mites. These species belonged to 29 different families, which together represent the whole food web in the cow pads.

Methods based on environmental DNA (eDNA) have recently proven efficient in mapping biodiversity in a simple and non-invasive way, by analyzing DNA from environmental samples of for instance water or soil. The newfound application on dung can be of great value for monitoring threatened insect species associated with dung, and can also be used to improve our understanding of the decomposition of organic material in nature. The results of the study have just been published in the internationally recognized journal Molecular Ecology.

Crucial resource and dirty work

Dung is an essential resource in nature. Both as a food source and as a habitat for a broad range of smaller organisms. Within insects alone, hundreds of species of beetles and flies are associated with dung, which they either feed on directly or use as hunting grounds for predating on other species. Apart from insects, a plethora of worms, mites and especially fungal species live in association with dung. These many creatures in the dung also attract a diversity of birds. Thus, the dung supports a miniature ecosystem, which is essential to the breakdown of organic matter. 

However, it can be an unmanageable – not to mention messy – work to identify the many species found in dung, and to investigate the ecological interactions between them.

Postdoc Eva Egelyng Sigsgaard, who is first author on the study, says:

”The eDNA method makes it possible to study dung-associated organisms more efficiently, as it does not depend on the visual identification of the animals. For instance, species that have recently been in contact with the dung, but are not present the moment the dung is collected, can still be detected. And species or individuals that are difficult to identify based on their visible characteristics, like the larvae of certain insects, can often be identified based on their DNA. Lots of species are dependent on dung, but many of them are in decline, and there is still much we don’t know about them. So being able to keep an eye on their distribution and abundance in an efficient way is really important.”

Improved monitoring of insects in Denmark

Dung as a source of eDNA provides possibilities for illuminating fundamental research questions on the conversion of organic material, but can also be applied in the monitoring and management of threatened species. Many of the insect species, which are associated with dung, are threatened in Denmark. This is due to a general lack of habitats with large animals grazing year-round.

Biologist at the Natural History Museum, Morten D. D. Hansen, who was part of the team behind the study, says:

“It has always been difficult to precisely detect changes in the dung fauna, but with this approach it will be much easier for us to document the effects of rewilding, like we are doing at the Mols Laboratory for instance.”

Surprising finding

Even a previously almost unknown insect species for Denmark was detected with the eDNA method. This was a moth fly named Psychoda grisescens. Moth flies are often found in dung, sludge and similar habitats, like drain pipes in bathrooms. The species in question is not on the official Danish species list, but was apparently found in a study from 2011, and has just recently been detected in Northen Sealand in another eDNA investigation (https://insektmobilen.snm.ku.dk/en/) – interestingly in samples from June 2019, just like in the current study. As moth flies are generally poorly studied, it is not unlikely that the species is in fact widely distributed in the country. 

According to senior author on the study, Associate professor Philip Francis Thomsen, the study demonstrates how little we know about our insect fauna, and that eDNA can be a supplemental approach for improving our understanding of ecological interactions and gaining more knowledge on rare or previously unknown species in the Danish fauna.

“The moth fly species we found is a great example of this. It would be interesting to do a targeted search for this species next summer”, he says.


Further information

The article in Molecular Ecology Environmental DNA metabarcoding of cow dung reveals taxonomic and functional diversity of invertebrate assemblages

 

Postdoc Eva Egelyng Sigsgaard
Department of Biology, Aarhus University
Mail: eva.sigsgaard@bio.au.dk
Mobile: (+45) 2094 4266

Associate Professor Philip Francis Thomsen
Department of Biology, Aarhus University
Mail: pfthomsen@bio.au.dk
Mobile: (+45) 2714 2046

Department of Biology, Sustainability