Biological fieldwork can mean trips to exotic places. The most common method is to send a few eager graduate students armed with camera traps and several weeks of spare time. But perhaps not for much longer. A paper published in Current Biology suggests an easier method: simply swabbing (擦拭) nearby leaves for DNA.
The DNA in question is called "environmental DNA" (eDNA for short). It refers to all the genetic information that animals leave behind as they go about their daily business: breathing, urinating, or interacting with their environment in any way. In recent years, genesequencing (基因测序) technology has become quick and sensitive enough to pick out genetic sequences from particular animals including humans from this eDNA.
One way of doing so is simply to blow air through filters (过滤器), and then analyse them to see which animals live nearby. Drs Gogarten and Lynggaard wondered if there might be a simpler approach. Air-sampling systems can take days to do their work. Maintenance must be done, and filters must be changed. But given that eDNA is literally blowing around ecosystems, the searchers wondered if it might be collecting on leaves.
The leaves of many plants are waxy (蜡质的) and somewhat sticky. The researchers theorised that eDNA might end up stuck to leaves and that it could subsequently be collected by swabbing them. They tested their theory in the dense rain forests of Kibale National Park, in Uganda. Using simple cotton swabs, and wearing masks and gloves to prevent polluting the samples with their own DNA, they visited three areas of the park and collected eight swabs at each site, and then took them back to Copenhagen for analysis.
The swabs revealed the presence of 26 birds, 24 mammals, one amphibian and one fish, with each swab containing DNA from eight animals on average. More than half the samples were good enough to work out the precise species they came from.
Swabbing for animals, then, seems to work. Moreover, it is cheap, easy and fast. Graduate students will have to be content spending less time sample-hunting in distant parts of the world.
