The science around DNA has developed exponentially in recent years: in the early 1990s, detection techniques for DNA were barely 'in their infancy'; But now, only decades later, we can extract ancient DNA not only from bones, but from the soil that our ancestors stepped on millennia ago or even from the 'glue' left by lice to adhere their nits to the hair of the mummies . That is, we extract genetic information almost from the air. Or almost without. Because two independent teams have analyzed the environmental DNA of two European zoos, detecting with great precision the species inside them. The results have just been published in the journal ' Current Biology ' (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 the seals feed or the manure smell of the deer waste, there were also traces of genetic information of the living inhabitants of the place. To test it, they chose samples from two different zoos: the Hamerton Zoo Park (in the UK) and the Copenhagen Zoo (in Denmark). And they found that their techniques, each one different, could identify those animals much better than they had imagined.
“Compared to what is found in rivers and lakes, finding DNA in the air is really very difficult, because it seems super diluted in the air,” explains Elizabeth Clare , principal investigator of the team of Queen Mary University, London. 'But our studies in zoos have not yet failed for different indicators, 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 zoo animals, but those outside its borders. On the one hand, the team led by Kristine Bohmann , from the University of Copenhagen, collected air samples using three different devices: a commercial water-based vacuum cleaner and two fans with filters, one of which was they the size of a golf ball. They collected air samples at three locations: the okapi barn, Rainforest House, and between the two enclosures. For their part, Clare's group used sensitive filters connected to vacuum pumps to collect more than 70 air samples from different locations in the zoo, both within the animal resting areas and the zoo environment.
The results of the two experiments exceeded his expectations. “When we analyzed the collected samples, we were able to identify DNA from 25 different species of animals , such as tigers, lemurs and dingoes, 17 of which were species known from zoos. 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. The animals were inside, but their DNA was leaking, ”Clare says.
For his part, Bohmann says that the results surprised them: “In just 40 samples, we detected 49 species that include mammals, birds, amphibians, reptiles and fish. At Rainforest House we even spotted the guppy fish in the pond, the two-toed sloth, and the boa. By taking air samples from 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, so the researchers believe a new window opens with 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 difficult-to-reach environments such as caves and burrows. They don't have 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 – Clare says. Air sampling could revolutionize terrestrial biomonitoring and provide new opportunities to track the composition of animal communities, as well as detect the invasion of non-native species. ”
Possible contamination of samples
It is not the first time that the detection of environmental DNA has been studied: for example, it is a method widely used 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 that the risk of contamination is high. We wanted to make sure that the species we detected were from the zoo and not, for example, from the laboratory. To make sure we didn't have any contaminating DNA floating in the air in the lab, we took air samples inside and sequenced it as well, ”explains Christina Lynggaard , 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 delighted 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 improves the strength of their work and clearly shows the potential of the technique. “Actually, we thought that the aspiration of animal DNA from 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.
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