Two independent research groups detect the presence of animals by collecting genetic material from the environment
The science around DNA has developed exponentially in recent years: in the early 1990s, DNA detection techniques were barely ‘in their infancy’; but now, just decades later, we can extract ancient DNA not just from bones, but from the ground, our ancestors walked on millennia ago or even from the ‘glue’ left behind by lice to adhere their nits to mummies ‘ hair. That is, we extract genetic information almost out of thin air. Or without the almost. Because two independent teams have analyzed the environmental DNA of two European zoos, detecting with great precision the species inside. The results have just been published in the journal ‘ Current Biology ‘ ( hereand here ).
The findings were made by two independent groups of researchers, one based in Denmark and the other in the UK and Canada. Both research groups set out to test whether airborne environmental DNA could be used to detect land animal species. That is, to demonstrate that, in addition to the fishy smell of the food that feeds the seals or the smell of manure from deer waste, there were also traces of genetic information from the living inhabitants of the place. To test it, they chose samples from two different zoos: the Hamerton Zoo Park (in the United Kingdom) and the Copenhagen Zoo. (in Denmark). And they found that his techniques, each of them different, could identify those animals much better than they had imagined.
“Compared to what you find in rivers and lakes, finding DNA in the air is really very difficult because it seems super-diluted in the air,” explains Elizabeth Clare, lead researcher on the team from the Queen Mary University of London. “But our zoo studies have not yet failed for different markers, genes, locations, and experimental approaches. Everything worked. And surprisingly well.”
Two ways to analyze the air for DNA
Each team used a different method to filter environmental DNA out of the air, but both techniques managed to detect not only the animals in the zoo, but those outside its borders. On the one hand, the team led by Kristine Bohmann, de la Universidad de Copenhague, recolectó muestras de aire utilizando tres dispositivos diferentes: una aspiradora comercial a base de agua y dos ventiladores con filtros, uno de ellos del tamaño de una pelota de golf. Recogieron muestras de aire en tres lugares: el establo de okapi, Rainforest House y entre ambos recintos. Por su parte, el grupo de Clare utilizó filtros sensibles conectados a bombas de vacío para recolectar más de 70 muestras de aire de diferentes lugares del zoológico, tanto dentro de las áreas de descanso de los animales como del entorno del zoológico.
The results of the two experiments exceeded their expectations. “When we analyzed the collected samples, we were able to identify DNA from 25 different species of animals, including tigers, lemurs, and dingoes, 17 of which were known zoo species. We were even able to collect environmental DNA from animals that were hundreds of meters from where we were testing without a significant drop in concentration, and even from buildings sealed in the open air. The animals were inside, but their DNA was leaking out,” says Clare.
For his part, Bohmann says the results surprised them: “In just 40 samples, we detected 49 species spanning mammals, birds, amphibians, reptiles, and fish. At Rainforest House we even spotted guppies in the pond, two-toed sloth, and boa. By taking air samples at a single outdoor site, we detected many of the animals with access to an outdoor enclosure in that part of the zoo, for example, kea, ostrich, and rhino.”
Both teams also detected the presence of food for zoo animals, such as chickens, cows, horses, and fish, which the researchers believe opens a new window on the potential of airborne environmental DNA detection techniques. “The non-invasive nature of this approach makes it particularly valuable for observing vulnerable or endangered species, as well as those in hard-to-reach environments such as caves and burrows. They don’t need to be visible for us to know they’re in the area if we can pick up traces of their DNA, literally out of nowhere,” says Clare. Air sampling could revolutionize terrestrial biomonitoring and provide new opportunities to track the composition of animal communities, as well as to detect the invasion of non-native species.”
Possible sample contamination
It is not the first time that the detection of environmental DNA has been studied: for example, it is a widely used method with water samples, to map species in aquatic environments. Even so, it is the first time that it has been done with airborne DNA since it contains a much greater challenge than water. “Air is a challenging substrate to work with as it surrounds everything, which means the risk of contamination is high. We wanted to make sure that the species we detected were from the zoo and not, say, from the lab. To make sure we didn’t have any contaminating DNA floating in the air in the lab, we sampled the air inside and sequenced that too,” explains Christina Lynggaard, a member of the Danish team and another of the authors of one of the studies.
The teams were unaware of each other’s work until the investigations were completed, but once they found out, they were pleased by the parallel nature of the experiments. Clare and Bohmann agree that having two research teams independently demonstrate that airborne environmental DNA can be used to monitor a variety of animal species greatly enhances the strength of their work and clearly shows the potential of the technique.
“Actually, we thought that sucking animal DNA out of the air would work,” adds Bohmann. This was a high-risk, high-reward science with the potential to push the boundaries of vertebrate biomonitoring. Clearly, the sky is not the limit.”
